Merge remote-tracking branch 'origin/master' into p/flake-update

.github/PULL_REQUEST_TEMPLATE.md

@@ -10,24 +10,6 @@
 
 <!-- Large change: Provide instructions to reviewers how to read the diff. -->
 
-# Checklist for maintainers
-
-<!-- Contributors: please leave this as is -->
-
-Maintainers: tick if completed or explain if not relevant
-
- - [ ] agreed on idea
- - [ ] agreed on implementation strategy
- - [ ] tests, as appropriate
-   - functional tests - `tests/**.sh`
-   - unit tests - `src/*/tests`
-   - integration tests - `tests/nixos/*`
- - [ ] documentation in the manual
- - [ ] documentation in the internal API docs
- - [ ] code and comments are self-explanatory
- - [ ] commit message explains why the change was made
- - [ ] new feature or incompatible change: updated release notes
-
 # Priorities
 
 Add :+1: to [pull requests you find important](https://github.com/NixOS/nix/pulls?q=is%3Aopen+sort%3Areactions-%2B1-desc).

.github/workflows/backport.yml

@@ -14,7 +14,7 @@ jobs:
     if: github.repository_owner == 'NixOS' && github.event.pull_request.merged == true && (github.event_name != 'labeled' || startsWith('backport', github.event.label.name))
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           ref: ${{ github.event.pull_request.head.sha }}
           # required to find all branches

.github/workflows/ci.yml

@@ -17,10 +17,10 @@ jobs:
     runs-on: ${{ matrix.os }}
     timeout-minutes: 60
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v23
       with:
         # The sandbox would otherwise be disabled by default on Darwin
         extra_nix_config: "sandbox = true"
@@ -58,11 +58,11 @@ jobs:
     outputs:
       installerURL: ${{ steps.prepare-installer.outputs.installerURL }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v23
       with:
         install_url: https://releases.nixos.org/nix/nix-2.13.3/install
     - uses: cachix/cachix-action@v12
@@ -82,9 +82,9 @@ jobs:
         os: [ubuntu-latest, macos-latest]
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v23
       with:
         install_url: '${{needs.installer.outputs.installerURL}}'
         install_options: "--tarball-url-prefix https://${{ env.CACHIX_NAME }}.cachix.org/serve"
@@ -108,10 +108,10 @@ jobs:
       needs.check_secrets.outputs.docker == 'true'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
-    - uses: cachix/install-nix-action@v22
+    - uses: cachix/install-nix-action@v23
       with:
         install_url: https://releases.nixos.org/nix/nix-2.13.3/install
     - run: echo CACHIX_NAME="$(echo $GITHUB_REPOSITORY-install-tests | tr "[A-Z]/" "[a-z]-")" >> $GITHUB_ENV

.github/workflows/hydra_status.yml

@@ -13,7 +13,7 @@ jobs:
     if: github.repository_owner == 'NixOS'
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - run: bash scripts/check-hydra-status.sh

CONTRIBUTING.md

@@ -30,8 +30,8 @@ Check out the [security policy](https://github.com/NixOS/nix/security/policy).
 
 2. Search for related issues that cover what you're going to work on. It could help to mention there that you will work on the issue.
 
-   Issues labeled ["good first issue"](https://github.com/NixOS/nix/labels/good-first-issue) should be relatively easy to fix and are likely to get merged quickly.
+   Issues labeled [good first issue](https://github.com/NixOS/nix/labels/good-first-issue) should be relatively easy to fix and are likely to get merged quickly.
-   Pull requests addressing issues labeled ["idea approved"](https://github.com/NixOS/nix/labels/idea%20approved) are especially welcomed by maintainers and will receive prioritised review.
+   Pull requests addressing issues labeled [idea approved](https://github.com/NixOS/nix/labels/idea%20approved) are especially welcomed by maintainers and will receive prioritised review.
 
 3. Check the [Nix reference manual](https://nixos.org/manual/nix/unstable/contributing/hacking.html) for information on building Nix and running its tests.
 
@@ -40,14 +40,27 @@ Check out the [security policy](https://github.com/NixOS/nix/security/policy).
 4. Make your changes!
 
 5. [Create a pull request](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/creating-a-pull-request) for your changes.
-   * [Mark the pull request as draft](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request) if you're not done with the changes.
-   * Make sure to have [a clean history of commits on your branch by using rebase](https://www.digitalocean.com/community/tutorials/how-to-rebase-and-update-a-pull-request).
    * Link related issues in your pull request to inform interested parties and future contributors about your change.
+   * Make sure to have [a clean history of commits on your branch by using rebase](https://www.digitalocean.com/community/tutorials/how-to-rebase-and-update-a-pull-request).
      If your pull request closes one or multiple issues, note that in the description using `Closes: #<number>`, as it will then happen automatically when your change is merged.
+   * [Mark the pull request as draft](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request) if you're not done with the changes.
 
 6. Do not expect your pull request to be reviewed immediately.
    Nix maintainers follow a [structured process for reviews and design decisions](https://github.com/NixOS/nix/tree/master/maintainers#project-board-protocol), which may or may not prioritise your work.
 
+   Following this checklist will make the process smoother for everyone:
+
+   - [ ] Fixes an [idea approved](https://github.com/NixOS/nix/labels/idea%20approved) issue
+   - [ ] Tests, as appropriate:
+     - Functional tests – [`tests/**.sh`](./tests)
+     - Unit tests – [`src/*/tests`](./src/)
+     - Integration tests – [`tests/nixos/*`](./tests/nixos)
+   - [ ] User documentation in the [manual](..doc/manual/src)
+   - [ ] API documentation in header files
+   - [ ] Code and comments are self-explanatory
+   - [ ] Commit message explains **why** the change was made
+   - [ ] New feature or incompatible change: updated [release notes](./doc/manual/src/release-notes/rl-next.md)
+
 7. If you need additional feedback or help to getting pull request into shape, ask other contributors using [@mentions](https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#mentioning-people-and-teams).
 
 ## Making changes to the Nix manual

doc/manual/generate-manpage.nix

@@ -98,7 +98,7 @@ let
                 (option ? labels)
                 (concatStringsSep " " (map (s: "*${s}*") option.labels));
             in trim ''
-              - `--${name}` ${shortName} ${labels}
+              - <span id="opt-${name}">[`--${name}`](#opt-${name})</span> ${shortName} ${labels}
 
                 ${option.description}
             '';

doc/manual/src/SUMMARY.md.in

@@ -100,6 +100,7 @@
   - [File System Object](architecture/file-system-object.md)
 - [Protocols](protocols/protocols.md)
   - [Serving Tarball Flakes](protocols/tarball-fetcher.md)
+  - [Derivation "ATerm" file format](protocols/derivation-aterm.md)
 - [Glossary](glossary.md)
 - [Contributing](contributing/contributing.md)
   - [Hacking](contributing/hacking.md)

doc/manual/src/command-ref/nix-env/install.md

@@ -30,7 +30,7 @@ a number of possible ways:
     derivation with the highest *priority* is used. A derivation can
     define a priority by declaring the `meta.priority` attribute. This
     attribute should be a number, with a higher value denoting a lower
-    priority. The default priority is `0`.
+    priority. The default priority is `5`.
 
     If there are multiple matching derivations with the same priority,
     then the derivation with the highest version will be installed.

doc/manual/src/command-ref/nix-store/query.md

@@ -5,8 +5,8 @@
 # Synopsis
 
 `nix-store` {`--query` | `-q`}
-  {`--outputs` | `--requisites` | `-R` | `--references` |
+  {`--outputs` | `--requisites` | `-R` | `--references` | `--referrers` |
-  `--referrers` | `--referrers-closure` | `--deriver` | `-d` |
+  `--referrers-closure` | `--deriver` | `-d` | `--valid-derivers` |
   `--graph` | `--tree` | `--binding` *name* | `-b` *name* | `--hash` |
   `--size` | `--roots`}
   [`--use-output`] [`-u`] [`--force-realise`] [`-f`]
@@ -82,13 +82,21 @@ symlink.
     in the Nix store that are dependent on *paths*.
 
   - `--deriver`; `-d`\
-    Prints the [deriver] of the store paths *paths*. If
+    Prints the [deriver] that was used to build the store paths *paths*. If
     the path has no deriver (e.g., if it is a source file), or if the
     deriver is not known (e.g., in the case of a binary-only
     deployment), the string `unknown-deriver` is printed.
+    The returned deriver is not guaranteed to exist in the local store, for
+    example when *paths* were substituted from a binary cache.
+    Use `--valid-derivers` instead to obtain valid paths only.
 
     [deriver]: ../../glossary.md#gloss-deriver
 
+  - `--valid-derivers`\
+    Prints a set of derivation files (`.drv`) which are supposed produce
+    said paths when realized. Might print nothing, for example for source paths
+    or paths subsituted from a binary cache.
+
   - `--graph`\
     Prints the references graph of the store paths *paths* in the format
     of the `dot` tool of AT\&T's [Graphviz

doc/manual/src/command-ref/nix-store/realise.md

@@ -1,6 +1,6 @@
 # Name
 
-`nix-store --realise` - realise specified store paths
+`nix-store --realise` - build or fetch store objects
 
 # Synopsis
 
@@ -8,33 +8,35 @@
 
 # Description
 
-The operation `--realise` essentially “builds” the specified store
-paths. Realisation is a somewhat overloaded term:
 
-  - If the store path is a *derivation*, realisation ensures that the
+Each of *paths* is processed as follows:
-    output paths of the derivation are [valid] (i.e.,
-    the output path and its closure exist in the file system). This
-    can be done in several ways. First, it is possible that the
-    outputs are already valid, in which case we are done
-    immediately. Otherwise, there may be [substitutes]
-    that produce the outputs (e.g., by downloading them). Finally, the
-    outputs can be produced by running the build task described
-    by the derivation.
 
-  - If the store path is not a derivation, realisation ensures that the
+- If the path leads to a [store derivation]:
-    specified path is valid (i.e., it and its closure exist in the file
+  1. If it is not [valid], substitute the store derivation file itself.
-    system). If the path is already valid, we are done immediately.
+  2. Realise its [output paths]:
-    Otherwise, the path and any missing paths in its closure may be
+    - Try to fetch from [substituters] the [store objects] associated with the output paths in the store derivation's [closure].
-    produced through substitutes. If there are no (successful)
+      - With [content-addressed derivations] (experimental): Determine the output paths to realise by querying content-addressed realisation entries in the [Nix database].
-    substitutes, realisation fails.
+    - For any store paths that cannot be substituted, produce the required store objects. This involves first realising all outputs of the derivation's dependencies and then running the derivation's [`builder`](@docroot@/language/derivations.md#attr-builder) executable. <!-- TODO: Link to build process page #8888 -->
+- Otherwise, and if the path is not already valid: Try to fetch the associated [store objects] in the path's [closure] from [substituters].
 
+If no substitutes are available and no store derivation is given, realisation fails.
+
+[store paths]: @docroot@/glossary.md#gloss-store-path
 [valid]: @docroot@/glossary.md#gloss-validity
-[substitutes]: @docroot@/glossary.md#gloss-substitute
+[store derivation]: @docroot@/glossary.md#gloss-store-derivation
+[output paths]: @docroot@/glossary.md#gloss-output-path
+[store objects]: @docroot@/glossary.md#gloss-store-object
+[closure]: @docroot@/glossary.md#gloss-closure
+[substituters]: @docroot@/command-ref/conf-file.md#conf-substituters
+[content-addressed derivations]: @docroot@/contributing/experimental-features.md#xp-feature-ca-derivations
+[Nix database]: @docroot@/glossary.md#gloss-nix-database
 
-The output path of each derivation is printed on standard output. (For
+The resulting paths are printed on standard output.
-non-derivations argument, the argument itself is printed.)
+For non-derivation arguments, the argument itself is printed.
 
-The following flags are available:
+{{#include ../status-build-failure.md}}
+
+# Options
 
   - `--dry-run`\
     Print on standard error a description of what packages would be
@@ -54,8 +56,6 @@ The following flags are available:
     previous build, the new output path is left in
     `/nix/store/name.check.`
 
-{{#include ../status-build-failure.md}}
-
 {{#include ./opt-common.md}}
 
 {{#include ../opt-common.md}}
@@ -67,8 +67,6 @@ The following flags are available:
 This operation is typically used to build [store derivation]s produced by
 [`nix-instantiate`](@docroot@/command-ref/nix-instantiate.md):
 
-[store derivation]: @docroot@/glossary.md#gloss-store-derivation
-
 ```console
 $ nix-store --realise $(nix-instantiate ./test.nix)
 /nix/store/31axcgrlbfsxzmfff1gyj1bf62hvkby2-aterm-2.3.1

doc/manual/src/command-ref/opt-common.md

@@ -2,56 +2,66 @@
 
 Most Nix commands accept the following command-line options:
 
-  - <span id="opt-help">[`--help`](#opt-help)</span>\
+- <span id="opt-help">[`--help`](#opt-help)</span>
+
   Prints out a summary of the command syntax and exits.
 
-  - <span id="opt-version">[`--version`](#opt-version)</span>\
+- <span id="opt-version">[`--version`](#opt-version)</span>
+
   Prints out the Nix version number on standard output and exits.
 
-  - <span id="opt-verbose">[`--verbose`](#opt-verbose)</span> / `-v`\
+- <span id="opt-verbose">[`--verbose`](#opt-verbose)</span> / `-v`
-    Increases the level of verbosity of diagnostic messages printed on
-    standard error. For each Nix operation, the information printed on
-    standard output is well-defined; any diagnostic information is
-    printed on standard error, never on standard output.
 
-    This option may be specified repeatedly. Currently, the following
+  Increases the level of verbosity of diagnostic messages printed on standard error.
-    verbosity levels exist:
+  For each Nix operation, the information printed on standard output is well-defined;
+  any diagnostic information is printed on standard error, never on standard output.
 
-      - 0\
+  This option may be specified repeatedly.
-        “Errors only”: only print messages explaining why the Nix
+  Currently, the following verbosity levels exist:
-        invocation failed.
 
-      - 1\
+  - `0` “Errors only”
-        “Informational”: print *useful* messages about what Nix is
-        doing. This is the default.
 
-      - 2\
+    Only print messages explaining why the Nix invocation failed.
-        “Talkative”: print more informational messages.
 
-      - 3\
+  - `1` “Informational”
-        “Chatty”: print even more informational messages.
 
-      - 4\
+    Print *useful* messages about what Nix is doing.
-        “Debug”: print debug information.
+    This is the default.
 
-      - 5\
+  - `2` “Talkative”
-        “Vomit”: print vast amounts of debug information.
 
-  - <span id="opt-quiet">[`--quiet`](#opt-quiet)</span>\
+    Print more informational messages.
-    Decreases the level of verbosity of diagnostic messages printed on
-    standard error. This is the inverse option to `-v` / `--verbose`.
 
-    This option may be specified repeatedly. See the previous verbosity
+  - `3` “Chatty”
-    levels list.
 
-  - <span id="opt-log-format">[`--log-format`](#opt-log-format)</span> *format*\
+    Print even more informational messages.
-    This option can be used to change the output of the log format, with
+
-    *format* being one of:
+  - `4` “Debug”
+   
+    Print debug information.
+
+  - `5` “Vomit”
+
+    Print vast amounts of debug information.
+
+- <span id="opt-quiet">[`--quiet`](#opt-quiet)</span>
+
+  Decreases the level of verbosity of diagnostic messages printed on standard error.
+  This is the inverse option to `-v` / `--verbose`.
+
+  This option may be specified repeatedly.
+  See the previous verbosity levels list.
+
+- <span id="opt-log-format">[`--log-format`](#opt-log-format)</span> *format*
+
+  This option can be used to change the output of the log format, with *format* being one of:
+
+  - `raw`
 
-      - raw\
     This is the raw format, as outputted by nix-build.
 
-      - internal-json\
+  - `internal-json`
+
     Outputs the logs in a structured manner.
 
     > **Warning**
@@ -60,100 +70,85 @@ Most Nix commands accept the following command-line options:
     > the error-messages (namely of the `msg`-field) can change
     > between releases.
 
-      - bar\
+  - `bar`
+
     Only display a progress bar during the builds.
 
-      - bar-with-logs\
+  - `bar-with-logs`
+
     Display the raw logs, with the progress bar at the bottom.
 
-  - <span id="opt-no-build-output">[`--no-build-output`](#opt-no-build-output)</span> / `-Q`\
+- <span id="opt-no-build-output">[`--no-build-output`](#opt-no-build-output)</span> / `-Q`
-    By default, output written by builders to standard output and
-    standard error is echoed to the Nix command's standard error. This
-    option suppresses this behaviour. Note that the builder's standard
-    output and error are always written to a log file in
-    `prefix/nix/var/log/nix`.
 
-  - <span id="opt-max-jobs">[`--max-jobs`](#opt-max-jobs)</span> / `-j` *number*\
+  By default, output written by builders to standard output and standard error is echoed to the Nix command's standard error.
-    Sets the maximum number of build jobs that Nix will perform in
+  This option suppresses this behaviour.
-    parallel to the specified number. Specify `auto` to use the number
+  Note that the builder's standard output and error are always written to a log file in `prefix/nix/var/log/nix`.
-    of CPUs in the system. The default is specified by the `max-jobs`
-    configuration setting, which itself defaults to `1`. A higher
-    value is useful on SMP systems or to exploit I/O latency.
 
-    Setting it to `0` disallows building on the local machine, which is
+- <span id="opt-max-jobs">[`--max-jobs`](#opt-max-jobs)</span> / `-j` *number*
-    useful when you want builds to happen only on remote builders.
 
-  - <span id="opt-cores">[`--cores`](#opt-cores)</span>\
+  Sets the maximum number of build jobs that Nix will perform in parallel to the specified number.
-    Sets the value of the `NIX_BUILD_CORES` environment variable in
+  Specify `auto` to use the number of CPUs in the system.
-    the invocation of builders. Builders can use this variable at
+  The default is specified by the `max-jobs` configuration setting, which itself defaults to `1`.
-    their discretion to control the maximum amount of parallelism. For
+  A higher value is useful on SMP systems or to exploit I/O latency.
-    instance, in Nixpkgs, if the derivation attribute
-    `enableParallelBuilding` is set to `true`, the builder passes the
-    `-jN` flag to GNU Make. It defaults to the value of the `cores`
-    configuration setting, if set, or `1` otherwise. The value `0`
-    means that the builder should use all available CPU cores in the
-    system.
 
-  - <span id="opt-max-silent-time">[`--max-silent-time`](#opt-max-silent-time)</span>\
+  Setting it to `0` disallows building on the local machine, which is useful when you want builds to happen only on remote builders.
-    Sets the maximum number of seconds that a builder can go without
-    producing any data on standard output or standard error. The
-    default is specified by the `max-silent-time` configuration
-    setting. `0` means no time-out.
 
-  - <span id="opt-timeout">[`--timeout`](#opt-timeout)</span>\
+- <span id="opt-cores">[`--cores`](#opt-cores)</span>
-    Sets the maximum number of seconds that a builder can run. The
-    default is specified by the `timeout` configuration setting. `0`
-    means no timeout.
 
-  - <span id="opt-keep-going">[`--keep-going`](#opt-keep-going)</span> / `-k`\
+  Sets the value of the `NIX_BUILD_CORES` environment variable in the invocation of builders.
-    Keep going in case of failed builds, to the greatest extent
+  Builders can use this variable at their discretion to control the maximum amount of parallelism.
-    possible. That is, if building an input of some derivation fails,
+  For instance, in Nixpkgs, if the derivation attribute `enableParallelBuilding` is set to `true`, the builder passes the `-jN` flag to GNU Make.
-    Nix will still build the other inputs, but not the derivation
+  It defaults to the value of the `cores` configuration setting, if set, or `1` otherwise.
-    itself. Without this option, Nix stops if any build fails (except
+  The value `0` means that the builder should use all available CPU cores in the system.
-    for builds of substitutes), possibly killing builds in progress (in
-    case of parallel or distributed builds).
 
-  - <span id="opt-keep-failed">[`--keep-failed`](#opt-keep-failed)</span> / `-K`\
+- <span id="opt-max-silent-time">[`--max-silent-time`](#opt-max-silent-time)</span>
-    Specifies that in case of a build failure, the temporary directory
-    (usually in `/tmp`) in which the build takes place should not be
-    deleted. The path of the build directory is printed as an
-    informational message.
 
-  - <span id="opt-fallback">[`--fallback`](#opt-fallback)</span>\
+  Sets the maximum number of seconds that a builder can go without producing any data on standard output or standard error.
-    Whenever Nix attempts to build a derivation for which substitutes
+  The default is specified by the `max-silent-time` configuration setting.
-    are known for each output path, but realising the output paths
+  `0` means no time-out.
-    through the substitutes fails, fall back on building the derivation.
 
-    The most common scenario in which this is useful is when we have
+- <span id="opt-timeout">[`--timeout`](#opt-timeout)</span>
-    registered substitutes in order to perform binary distribution from,
-    say, a network repository. If the repository is down, the
-    realisation of the derivation will fail. When this option is
-    specified, Nix will build the derivation instead. Thus, installation
-    from binaries falls back on installation from source. This option is
-    not the default since it is generally not desirable for a transient
-    failure in obtaining the substitutes to lead to a full build from
-    source (with the related consumption of resources).
 
-  - <span id="opt-readonly-mode">[`--readonly-mode`](#opt-readonly-mode)</span>\
+  Sets the maximum number of seconds that a builder can run.
-    When this option is used, no attempt is made to open the Nix
+  The default is specified by the `timeout` configuration setting.
-    database. Most Nix operations do need database access, so those
+  `0` means no timeout.
-    operations will fail.
 
-  - <span id="opt-arg">[`--arg`](#opt-arg)</span> *name* *value*\
+- <span id="opt-keep-going">[`--keep-going`](#opt-keep-going)</span> / `-k`
-    This option is accepted by `nix-env`, `nix-instantiate`,
-    `nix-shell` and `nix-build`. When evaluating Nix expressions, the
-    expression evaluator will automatically try to call functions that
-    it encounters. It can automatically call functions for which every
-    argument has a [default
-    value](@docroot@/language/constructs.md#functions) (e.g.,
-    `{ argName ?  defaultValue }: ...`). With `--arg`, you can also
-    call functions that have arguments without a default value (or
-    override a default value). That is, if the evaluator encounters a
-    function with an argument named *name*, it will call it with value
-    *value*.
 
-    For instance, the top-level `default.nix` in Nixpkgs is actually a
+  Keep going in case of failed builds, to the greatest extent possible.
-    function:
+  That is, if building an input of some derivation fails, Nix will still build the other inputs, but not the derivation itself.
+  Without this option, Nix stops if any build fails (except for builds of substitutes), possibly killing builds in progress (in case of parallel or distributed builds).
+
+- <span id="opt-keep-failed">[`--keep-failed`](#opt-keep-failed)</span> / `-K`
+
+  Specifies that in case of a build failure, the temporary directory (usually in `/tmp`) in which the build takes place should not be deleted.
+  The path of the build directory is printed as an informational message.
+
+- <span id="opt-fallback">[`--fallback`](#opt-fallback)</span>
+
+  Whenever Nix attempts to build a derivation for which substitutes are known for each output path, but realising the output paths through the substitutes fails, fall back on building the derivation.
+
+  The most common scenario in which this is useful is when we have registered substitutes in order to perform binary distribution from, say, a network repository.
+  If the repository is down, the realisation of the derivation will fail.
+  When this option is specified, Nix will build the derivation instead.
+  Thus, installation from binaries falls back on installation from source.
+  This option is not the default since it is generally not desirable for a transient failure in obtaining the substitutes to lead to a full build from source (with the related consumption of resources).
+
+- <span id="opt-readonly-mode">[`--readonly-mode`](#opt-readonly-mode)</span>
+
+  When this option is used, no attempt is made to open the Nix database.
+  Most Nix operations do need database access, so those operations will fail.
+
+- <span id="opt-arg">[`--arg`](#opt-arg)</span> *name* *value*
+
+  This option is accepted by `nix-env`, `nix-instantiate`, `nix-shell` and `nix-build`.
+  When evaluating Nix expressions, the expression evaluator will automatically try to call functions that it encounters.
+  It can automatically call functions for which every argument has a [default value](@docroot@/language/constructs.md#functions) (e.g., `{ argName ?  defaultValue }: ...`).
+
+  With `--arg`, you can also call functions that have arguments without a default value (or override a default value).
+  That is, if the evaluator encounters a function with an argument named *name*, it will call it with value *value*.
+
+  For instance, the top-level `default.nix` in Nixpkgs is actually a function:
 
   ```nix
   { # The system (e.g., `i686-linux') for which to build the packages.
@@ -162,57 +157,49 @@ Most Nix commands accept the following command-line options:
   }: ...
   ```
 
-    So if you call this Nix expression (e.g., when you do `nix-env --install --attr
+  So if you call this Nix expression (e.g., when you do `nix-env --install --attr pkgname`), the function will be called automatically using the value [`builtins.currentSystem`](@docroot@/language/builtins.md) for the `system` argument.
-    pkgname`), the function will be called automatically using the
+  You can override this using `--arg`, e.g., `nix-env --install --attr pkgname --arg system \"i686-freebsd\"`.
-    value [`builtins.currentSystem`](@docroot@/language/builtins.md) for
+  (Note that since the argument is a Nix string literal, you have to escape the quotes.)
-    the `system` argument. You can override this using `--arg`, e.g.,
-    `nix-env --install --attr pkgname --arg system \"i686-freebsd\"`. (Note that
-    since the argument is a Nix string literal, you have to escape the
-    quotes.)
 
-  - <span id="opt-argstr">[`--argstr`](#opt-argstr)</span> *name* *value*\
+- <span id="opt-argstr">[`--argstr`](#opt-argstr)</span> *name* *value*
-    This option is like `--arg`, only the value is not a Nix
-    expression but a string. So instead of `--arg system
-    \"i686-linux\"` (the outer quotes are to keep the shell happy) you
-    can say `--argstr system i686-linux`.
 
-  - <span id="opt-attr">[`--attr`](#opt-attr)</span> / `-A` *attrPath*\
+  This option is like `--arg`, only the value is not a Nix expression but a string.
-    Select an attribute from the top-level Nix expression being
+  So instead of `--arg system \"i686-linux\"` (the outer quotes are to keep the shell happy) you can say `--argstr system i686-linux`.
-    evaluated. (`nix-env`, `nix-instantiate`, `nix-build` and
+
-    `nix-shell` only.) The *attribute path* *attrPath* is a sequence
+- <span id="opt-attr">[`--attr`](#opt-attr)</span> / `-A` *attrPath*
-    of attribute names separated by dots. For instance, given a
+
-    top-level Nix expression *e*, the attribute path `xorg.xorgserver`
+  Select an attribute from the top-level Nix expression being evaluated.
-    would cause the expression `e.xorg.xorgserver` to be used. See
+  (`nix-env`, `nix-instantiate`, `nix-build` and `nix-shell` only.)
-    [`nix-env --install`](@docroot@/command-ref/nix-env/install.md) for some
+  The *attribute path* *attrPath* is a sequence of attribute names separated by dots.
-    concrete examples.
+  For instance, given a top-level Nix expression *e*, the attribute path `xorg.xorgserver` would cause the expression `e.xorg.xorgserver` to be used.
+  See [`nix-env --install`](@docroot@/command-ref/nix-env/install.md) for some concrete examples.
 
   In addition to attribute names, you can also specify array indices.
   For instance, the attribute path `foo.3.bar` selects the `bar`
   attribute of the fourth element of the array in the `foo` attribute
   of the top-level expression.
 
-  - <span id="opt-expr">[`--expr`](#opt-expr)</span> / `-E`\
+- <span id="opt-expr">[`--expr`](#opt-expr)</span> / `-E`
-    Interpret the command line arguments as a list of Nix expressions to
-    be parsed and evaluated, rather than as a list of file names of Nix
-    expressions. (`nix-instantiate`, `nix-build` and `nix-shell` only.)
 
-    For `nix-shell`, this option is commonly used to give you a shell in
+  Interpret the command line arguments as a list of Nix expressions to be parsed and evaluated, rather than as a list of file names of Nix expressions.
-    which you can build the packages returned by the expression. If you
+  (`nix-instantiate`, `nix-build` and `nix-shell` only.)
-    want to get a shell which contain the *built* packages ready for
+
-    use, give your expression to the `nix-shell --packages ` convenience flag
+  For `nix-shell`, this option is commonly used to give you a shell in which you can build the packages returned by the expression.
-    instead.
+  If you want to get a shell which contain the *built* packages ready for use, give your expression to the `nix-shell --packages ` convenience flag instead.
+
+- <span id="opt-I">[`-I`](#opt-I)</span> *path*
 
-  - <span id="opt-I">[`-I`](#opt-I)</span> *path*\
   Add an entry to the [Nix expression search path](@docroot@/command-ref/conf-file.md#conf-nix-path).
   This option may be given multiple times.
   Paths added through `-I` take precedence over [`NIX_PATH`](@docroot@/command-ref/env-common.md#env-NIX_PATH).
 
-  - <span id="opt-option">[`--option`](#opt-option)</span> *name* *value*\
+- <span id="opt-option">[`--option`](#opt-option)</span> *name* *value*
-    Set the Nix configuration option *name* to *value*. This overrides
-    settings in the Nix configuration file (see nix.conf5).
 
-  - <span id="opt-repair">[`--repair`](#opt-repair)</span>\
+  Set the Nix configuration option *name* to *value*.
-    Fix corrupted or missing store paths by redownloading or rebuilding
+  This overrides settings in the Nix configuration file (see nix.conf5).
-    them. Note that this is slow because it requires computing a
+
-    cryptographic hash of the contents of every path in the closure of
+- <span id="opt-repair">[`--repair`](#opt-repair)</span>
-    the build. Also note the warning under `nix-store --repair-path`.
+
+  Fix corrupted or missing store paths by redownloading or rebuilding them.
+  Note that this is slow because it requires computing a cryptographic hash of the contents of every path in the closure of the build.
+  Also note the warning under `nix-store --repair-path`.

doc/manual/src/glossary.md

@@ -33,7 +33,7 @@
 
   Ensure a [store path] is [valid][validity].
 
-  This means either running the `builder` executable as specified in the corresponding [derivation] or fetching a pre-built [store object] from a [substituter].
+  This means either running the [`builder`](@docroot@/language/derivations.md#attr-builder) executable as specified in the corresponding [derivation], or fetching a pre-built [store object] from a [substituter], or delegating to a [remote builder](@docroot@/advanced-topics/distributed-builds.html) and retrieving the outputs. <!-- TODO: link [running] to build process page, #8888 -->
 
   See [`nix-build`](./command-ref/nix-build.md) and [`nix-store --realise`](@docroot@/command-ref/nix-store/realise.md).
 
@@ -197,9 +197,15 @@
 
   [closure]: #gloss-closure
 
+- [output]{#gloss-output}
+
+  A [store object] produced by a [derivation].
+
+  [output]: #gloss-output
+
 - [output path]{#gloss-output-path}
 
-  A [store path] produced by a [derivation].
+  The [store path] to the [output] of a [derivation].
 
   [output path]: #gloss-output-path
 

doc/manual/src/language/derivations.md

@@ -17,7 +17,7 @@ the attributes of which specify the inputs of the build.
     string. This is used as a symbolic name for the package by
     `nix-env`, and it is appended to the output paths of the derivation.
 
-  - There must be an attribute named `builder` that identifies the
+  - There must be an attribute named [`builder`]{#attr-builder} that identifies the
     program that is executed to perform the build. It can be either a
     derivation or a source (a local file reference, e.g.,
     `./builder.sh`).

doc/manual/src/protocols/derivation-aterm.md

@@ -0,0 +1,19 @@
+# Derivation "ATerm" file format
+
+For historical reasons, [derivations](@docroot@/glossary.md#gloss-store-derivation) are stored on-disk in [ATerm](https://homepages.cwi.nl/~daybuild/daily-books/technology/aterm-guide/aterm-guide.html) format.
+
+Derivations are serialised in one of the following formats:
+
+- ```
+  Derive(...)
+  ```
+
+  For all stable derivations.
+
+- ```
+  DrvWithVersion(<version-string>, ...)
+  ```
+
+  The only `version-string`s that are in use today are for [experimental features](@docroot@/contributing/experimental-features.md):
+
+  - `"xp-dyn-drv"` for the [`dynamic-derivations`](@docroot@/contributing/experimental-features.md#xp-feature-dynamic-derivations) experimental feature.

doc/manual/src/release-notes/rl-next.md

@@ -24,3 +24,7 @@
   It is part of the [`dynamic-derivations`](@docroot@/contributing/experimental-features.md#xp-feature-dynamic-derivations) experimental feature.
 
 - Flake follow paths at depths greater than 2 are now handled correctly, preventing "follows a non-existent input" errors.
+
+- [`nix-store --query`](@docroot@/command-ref/nix-store/query.md) gained a new type of query: `--valid-derivers`. It returns all `.drv` files in the local store that *can be* used to build the output passed in argument.
+This is in contrast to `--deriver`, which returns the single `.drv` file that *was actually* used to build the output passed in argument. In case the output was substituted from a binary cache,
+this `.drv` file may only exist on said binary cache and not locally.

perl/lib/Nix/Store.xs

@@ -324,7 +324,7 @@ SV * derivationFromPath(char * drvPath)
             hv_stores(hash, "outputs", newRV((SV *) outputs));
 
             AV * inputDrvs = newAV();
-            for (auto & i : drv.inputDrvs)
+            for (auto & i : drv.inputDrvs.map)
                 av_push(inputDrvs, newSVpv(store()->printStorePath(i.first).c_str(), 0)); // !!! ignores i->second
             hv_stores(hash, "inputDrvs", newRV((SV *) inputDrvs));
 

src/build-remote/build-remote.cc

@@ -314,7 +314,7 @@ connected:
             //
             // 2. Changing the `inputSrcs` set changes the associated
             //    output ids, which break CA derivations
-            if (!drv.inputDrvs.empty())
+            if (!drv.inputDrvs.map.empty())
                 drv.inputSrcs = store->parseStorePathSet(inputs);
             optResult = sshStore->buildDerivation(*drvPath, (const BasicDerivation &) drv);
             auto & result = *optResult;

src/libcmd/built-path.cc

@@ -58,6 +58,28 @@ StorePathSet BuiltPath::outPaths() const
     );
 }
 
+SingleDerivedPath::Built SingleBuiltPath::Built::discardOutputPath() const
+{
+    return SingleDerivedPath::Built {
+        .drvPath = make_ref<SingleDerivedPath>(drvPath->discardOutputPath()),
+        .output = output.first,
+    };
+}
+
+SingleDerivedPath SingleBuiltPath::discardOutputPath() const
+{
+    return std::visit(
+        overloaded{
+            [](const SingleBuiltPath::Opaque & p) -> SingleDerivedPath {
+                return p;
+            },
+            [](const SingleBuiltPath::Built & b) -> SingleDerivedPath {
+                return b.discardOutputPath();
+            },
+        }, raw()
+    );
+}
+
 nlohmann::json BuiltPath::Built::toJSON(const Store & store) const
 {
     nlohmann::json res;

src/libcmd/built-path.hh

@@ -9,6 +9,8 @@ struct SingleBuiltPathBuilt {
     ref<SingleBuiltPath> drvPath;
     std::pair<std::string, StorePath> output;
 
+    SingleDerivedPathBuilt discardOutputPath() const;
+
     std::string to_string(const Store & store) const;
     static SingleBuiltPathBuilt parse(const Store & store, std::string_view, std::string_view);
     nlohmann::json toJSON(const Store & store) const;
@@ -34,6 +36,8 @@ struct SingleBuiltPath : _SingleBuiltPathRaw {
 
     StorePath outPath() const;
 
+    SingleDerivedPath discardOutputPath() const;
+
     static SingleBuiltPath parse(const Store & store, std::string_view);
     nlohmann::json toJSON(const Store & store) const;
 };

src/libcmd/repl.cc

@@ -490,33 +490,38 @@ bool NixRepl::processLine(std::string line)
              << "\n"
              << "  <expr>                       Evaluate and print expression\n"
              << "  <x> = <expr>                 Bind expression to variable\n"
-             << "  :a <expr>     Add attributes from resulting set to scope\n"
+             << "  :a, :add <expr>              Add attributes from resulting set to scope\n"
              << "  :b <expr>                    Build a derivation\n"
-             << "  :bl <expr>    Build a derivation, creating GC roots in the working directory\n"
+             << "  :bl <expr>                   Build a derivation, creating GC roots in the\n"
-             << "  :e <expr>     Open package or function in $EDITOR\n"
+             << "                               working directory\n"
-             << "  :i <expr>     Build derivation, then install result into current profile\n"
+             << "  :e, :edit <expr>             Open package or function in $EDITOR\n"
-             << "  :l <path>     Load Nix expression and add it to scope\n"
+             << "  :i <expr>                    Build derivation, then install result into\n"
-             << "  :lf <ref>     Load Nix flake and add it to scope\n"
+             << "                               current profile\n"
-             << "  :p <expr>     Evaluate and print expression recursively\n"
+             << "  :l, :load <path>             Load Nix expression and add it to scope\n"
-             << "  :q            Exit nix-repl\n"
+             << "  :lf, :load-flake <ref>       Load Nix flake and add it to scope\n"
-             << "  :r            Reload all files\n"
+             << "  :p, :print <expr>            Evaluate and print expression recursively\n"
-             << "  :sh <expr>    Build dependencies of derivation, then start nix-shell\n"
+             << "  :q, :quit                    Exit nix-repl\n"
+             << "  :r, :reload                  Reload all files\n"
+             << "  :sh <expr>                   Build dependencies of derivation, then start\n"
+             << "                               nix-shell\n"
              << "  :t <expr>                    Describe result of evaluation\n"
              << "  :u <expr>                    Build derivation, then start nix-shell\n"
              << "  :doc <expr>                  Show documentation of a builtin function\n"
              << "  :log <expr>                  Show logs for a derivation\n"
-             << "  :te [bool]    Enable, disable or toggle showing traces for errors\n"
+             << "  :te, :trace-enable [bool]    Enable, disable or toggle showing traces for\n"
+             << "                               errors\n"
+             << "  :?, :help                    Brings up this help menu\n"
              ;
         if (state->debugRepl) {
              std::cout
              << "\n"
              << "        Debug mode commands\n"
              << "  :env             Show env stack\n"
-             << "  :bt           Show trace stack\n"
+             << "  :bt, :backtrace  Show trace stack\n"
              << "  :st              Show current trace\n"
              << "  :st <idx>        Change to another trace in the stack\n"
-             << "  :c            Go until end of program, exception, or builtins.break\n"
+             << "  :c, :continue    Go until end of program, exception, or builtins.break\n"
-             << "  :s            Go one step\n"
+             << "  :s, :step        Go one step\n"
              ;
         }
 

src/libexpr/eval-settings.hh

@@ -21,7 +21,7 @@ struct EvalSettings : Config
         R"(
           List of directories to be searched for `<...>` file references
 
-          In particular, outside of [pure evaluation mode](#conf-pure-evaluation), this determines the value of
+          In particular, outside of [pure evaluation mode](#conf-pure-eval), this determines the value of
           [`builtins.nixPath`](@docroot@/language/builtin-constants.md#builtins-nixPath).
         )"};
 

src/libexpr/flake/flake.cc

@@ -520,11 +520,6 @@ LockedFlake lockFlake(
                             }
                         }
 
-                        auto localPath(parentPath);
-                        // If this input is a path, recurse it down.
-                        // This allows us to resolve path inputs relative to the current flake.
-                        if ((*input.ref).input.getType() == "path")
-                            localPath = absPath(*input.ref->input.getSourcePath(), parentPath);
                         computeLocks(
                             mustRefetch
                             ? getFlake(state, oldLock->lockedRef, false, flakeCache, inputPath).inputs

src/libexpr/primops.cc

@@ -1252,15 +1252,13 @@ drvName, Bindings * attrs, Value & v)
                 state.store->computeFSClosure(d.drvPath, refs);
                 for (auto & j : refs) {
                     drv.inputSrcs.insert(j);
-                    if (j.isDerivation())
+                    if (j.isDerivation()) {
-                        drv.inputDrvs[j] = state.store->readDerivation(j).outputNames();
+                        drv.inputDrvs.map[j].value = state.store->readDerivation(j).outputNames();
+                    }
                 }
             },
             [&](const NixStringContextElem::Built & b) {
-                if (auto * p = std::get_if<DerivedPath::Opaque>(&*b.drvPath))
+                drv.inputDrvs.ensureSlot(*b.drvPath).value.insert(b.output);
-                    drv.inputDrvs[p->path].insert(b.output);
-                else
-                    throw UnimplementedError("Dependencies on the outputs of dynamic derivations are not yet supported");
             },
             [&](const NixStringContextElem::Opaque & o) {
                 drv.inputSrcs.insert(o.path);
@@ -1520,15 +1518,25 @@ static RegisterPrimOp primop_storePath({
 
 static void prim_pathExists(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
+    auto & arg = *args[0];
+
     /* We don’t check the path right now, because we don’t want to
        throw if the path isn’t allowed, but just return false (and we
        can’t just catch the exception here because we still want to
-       throw if something in the evaluation of `*args[0]` tries to
+       throw if something in the evaluation of `arg` tries to
        access an unauthorized path). */
-    auto path = realisePath(state, pos, *args[0], { .checkForPureEval = false });
+    auto path = realisePath(state, pos, arg, { .checkForPureEval = false });
+
+    /* SourcePath doesn't know about trailing slash. */
+    auto mustBeDir = arg.type() == nString && arg.str().ends_with("/");
 
     try {
-        v.mkBool(state.checkSourcePath(path).pathExists());
+        auto checked = state.checkSourcePath(path);
+        auto exists = checked.pathExists();
+        if (exists && mustBeDir) {
+            exists = checked.lstat().type == InputAccessor::tDirectory;
+        }
+        v.mkBool(exists);
     } catch (SysError & e) {
         /* Don't give away info from errors while canonicalising
            ‘path’ in restricted mode. */

src/libstore/build/create-derivation-and-realise-goal.cc

@@ -96,7 +96,7 @@ void CreateDerivationAndRealiseGoal::getDerivation()
         auto drvPath = StorePath::dummy;
         try {
             drvPath = resolveDerivedPath(worker.store, *drvReq);
-        } catch (MissingRealisation) {
+        } catch (MissingRealisation &) {
             return std::nullopt;
         }
         return worker.evalStore.isValidPath(drvPath) || worker.store.isValidPath(drvPath)

src/libstore/build/derivation-goal.cc

@@ -350,24 +350,36 @@ void DerivationGoal::gaveUpOnSubstitution()
 
     /* The inputs must be built before we can build this goal. */
     inputDrvOutputs.clear();
-    if (useDerivation)
+    if (useDerivation) {
-        for (auto & i : dynamic_cast<Derivation *>(drv.get())->inputDrvs) {
+        std::function<void(ref<SingleDerivedPath>, const DerivedPathMap<StringSet>::ChildNode &)> addWaiteeDerivedPath;
+
+        addWaiteeDerivedPath = [&](ref<SingleDerivedPath> inputDrv, const DerivedPathMap<StringSet>::ChildNode & inputNode) {
+            if (!inputNode.value.empty())
+                addWaitee(worker.makeGoal(
+                    DerivedPath::Built {
+                        .drvPath = inputDrv,
+                        .outputs = inputNode.value,
+                    },
+                    buildMode == bmRepair ? bmRepair : bmNormal));
+            for (const auto & [outputName, childNode] : inputNode.childMap)
+                addWaiteeDerivedPath(
+                    make_ref<SingleDerivedPath>(SingleDerivedPath::Built { inputDrv, outputName }),
+                    childNode);
+        };
+
+        for (const auto & [inputDrvPath, inputNode] : dynamic_cast<Derivation *>(drv.get())->inputDrvs.map) {
             /* Ensure that pure, non-fixed-output derivations don't
                depend on impure derivations. */
             if (experimentalFeatureSettings.isEnabled(Xp::ImpureDerivations) && drv->type().isPure() && !drv->type().isFixed()) {
-                auto inputDrv = worker.evalStore.readDerivation(i.first);
+                auto inputDrv = worker.evalStore.readDerivation(inputDrvPath);
                 if (!inputDrv.type().isPure())
                     throw Error("pure derivation '%s' depends on impure derivation '%s'",
                         worker.store.printStorePath(drvPath),
-                        worker.store.printStorePath(i.first));
+                        worker.store.printStorePath(inputDrvPath));
             }
 
-            addWaitee(worker.makeGoal(
+            addWaiteeDerivedPath(makeConstantStorePathRef(inputDrvPath), inputNode);
-                DerivedPath::Built {
+        }
-                    .drvPath = makeConstantStorePathRef(i.first),
-                    .outputs = i.second,
-                },
-                buildMode == bmRepair ? bmRepair : bmNormal));
     }
 
     /* Copy the input sources from the eval store to the build
@@ -501,7 +513,7 @@ void DerivationGoal::inputsRealised()
                 return ia.deferred;
             },
             [&](const DerivationType::ContentAddressed & ca) {
-                return !fullDrv.inputDrvs.empty() && (
+                return !fullDrv.inputDrvs.map.empty() && (
                     ca.fixed
                     /* Can optionally resolve if fixed, which is good
                        for avoiding unnecessary rebuilds. */
@@ -515,7 +527,7 @@ void DerivationGoal::inputsRealised()
             }
         }, drvType.raw);
 
-        if (resolveDrv && !fullDrv.inputDrvs.empty()) {
+        if (resolveDrv && !fullDrv.inputDrvs.map.empty()) {
             experimentalFeatureSettings.require(Xp::CaDerivations);
 
             /* We are be able to resolve this derivation based on the
@@ -552,11 +564,13 @@ void DerivationGoal::inputsRealised()
             return;
         }
 
-        for (auto & [depDrvPath, wantedDepOutputs] : fullDrv.inputDrvs) {
+        std::function<void(const StorePath &, const DerivedPathMap<StringSet>::ChildNode &)> accumInputPaths;
+
+        accumInputPaths = [&](const StorePath & depDrvPath, const DerivedPathMap<StringSet>::ChildNode & inputNode) {
             /* Add the relevant output closures of the input derivation
                `i' as input paths.  Only add the closures of output paths
                that are specified as inputs. */
-            for (auto & j : wantedDepOutputs) {
+            auto getOutput = [&](const std::string & outputName) {
                 /* TODO (impure derivations-induced tech debt):
                    Tracking input derivation outputs statefully through the
                    goals is error prone and has led to bugs.
@@ -568,21 +582,30 @@ void DerivationGoal::inputsRealised()
                    a representation in the store, which is a usability problem
                    in itself. When implementing this logic entirely with lookups
                    make sure that they're cached. */
-                if (auto outPath = get(inputDrvOutputs, { depDrvPath, j })) {
+                if (auto outPath = get(inputDrvOutputs, { depDrvPath, outputName })) {
-                    worker.store.computeFSClosure(*outPath, inputPaths);
+                    return *outPath;
                 }
                 else {
                     auto outMap = worker.evalStore.queryDerivationOutputMap(depDrvPath);
-                    auto outMapPath = outMap.find(j);
+                    auto outMapPath = outMap.find(outputName);
                     if (outMapPath == outMap.end()) {
                         throw Error(
                             "derivation '%s' requires non-existent output '%s' from input derivation '%s'",
-                            worker.store.printStorePath(drvPath), j, worker.store.printStorePath(depDrvPath));
+                            worker.store.printStorePath(drvPath), outputName, worker.store.printStorePath(depDrvPath));
-                    }
-                    worker.store.computeFSClosure(outMapPath->second, inputPaths);
-                }
                     }
+                    return outMapPath->second;
                 }
+            };
+
+            for (auto & outputName : inputNode.value)
+                worker.store.computeFSClosure(getOutput(outputName), inputPaths);
+
+            for (auto & [outputName, childNode] : inputNode.childMap)
+                accumInputPaths(getOutput(outputName), childNode);
+        };
+
+        for (auto & [depDrvPath, depNode] : fullDrv.inputDrvs.map)
+            accumInputPaths(depDrvPath, depNode);
     }
 
     /* Second, the input sources. */
@@ -1475,22 +1498,24 @@ void DerivationGoal::waiteeDone(GoalPtr waitee, ExitCode result)
     if (!useDerivation) return;
     auto & fullDrv = *dynamic_cast<Derivation *>(drv.get());
 
-    auto * dg = tryGetConcreteDrvGoal(waitee);
+    std::optional info = tryGetConcreteDrvGoal(waitee);
-    if (!dg) return;
+    if (!info) return;
+    const auto & [dg, drvReq] = *info;
 
-    auto outputs = fullDrv.inputDrvs.find(dg->drvPath);
+    auto * nodeP = fullDrv.inputDrvs.findSlot(drvReq.get());
-    if (outputs == fullDrv.inputDrvs.end()) return;
+    if (!nodeP) return;
+    auto & outputs = nodeP->value;
 
-    for (auto & outputName : outputs->second) {
+    for (auto & outputName : outputs) {
-        auto buildResult = dg->getBuildResult(DerivedPath::Built {
+        auto buildResult = dg.get().getBuildResult(DerivedPath::Built {
-            .drvPath = makeConstantStorePathRef(dg->drvPath),
+            .drvPath = makeConstantStorePathRef(dg.get().drvPath),
             .outputs = OutputsSpec::Names { outputName },
         });
         if (buildResult.success()) {
             auto i = buildResult.builtOutputs.find(outputName);
             if (i != buildResult.builtOutputs.end())
                 inputDrvOutputs.insert_or_assign(
-                    { dg->drvPath, outputName },
+                    { dg.get().drvPath, outputName },
                     i->second.outPath);
         }
     }

src/libstore/build/worker.cc

@@ -594,11 +594,14 @@ GoalPtr upcast_goal(std::shared_ptr<DerivationGoal> subGoal)
     return subGoal;
 }
 
-const DerivationGoal * tryGetConcreteDrvGoal(GoalPtr waitee)
+std::optional<std::pair<std::reference_wrapper<const DerivationGoal>, std::reference_wrapper<const SingleDerivedPath>>> tryGetConcreteDrvGoal(GoalPtr waitee)
 {
     auto * odg = dynamic_cast<CreateDerivationAndRealiseGoal *>(&*waitee);
-    if (!odg) return nullptr;
+    if (!odg) return std::nullopt;
-    return &*odg->concreteDrvGoal;
+    return {{
+        std::cref(*odg->concreteDrvGoal),
+        std::cref(*odg->drvReq),
+    }};
 }
 
 }

src/libstore/build/worker.hh

@@ -49,7 +49,8 @@ typedef std::chrono::time_point<std::chrono::steady_clock> steady_time_point;
  * we have made the function, written in `worker.cc` where all the goal
  * types are visible, and use it instead.
  */
-const DerivationGoal * tryGetConcreteDrvGoal(GoalPtr waitee);
+
+std::optional<std::pair<std::reference_wrapper<const DerivationGoal>, std::reference_wrapper<const SingleDerivedPath>>> tryGetConcreteDrvGoal(GoalPtr waitee);
 
 /**
  * A mapping used to remember for each child process to what goal it

src/libstore/derivations.cc

@@ -136,7 +136,7 @@ StorePath writeDerivation(Store & store,
     const Derivation & drv, RepairFlag repair, bool readOnly)
 {
     auto references = drv.inputSrcs;
-    for (auto & i : drv.inputDrvs)
+    for (auto & i : drv.inputDrvs.map)
         references.insert(i.first);
     /* Note that the outputs of a derivation are *not* references
        (that can be missing (of course) and should not necessarily be
@@ -154,8 +154,9 @@ static void expect(std::istream & str, std::string_view s)
 {
     char s2[s.size()];
     str.read(s2, s.size());
-    if (std::string(s2, s.size()) != s)
+    std::string_view s2View { s2, s.size() };
-        throw FormatError("expected string '%1%'", s);
+    if (s2View != s)
+        throw FormatError("expected string '%s', got '%s'", s, s2View);
 }
 
 
@@ -207,23 +208,27 @@ static bool endOfList(std::istream & str)
 static StringSet parseStrings(std::istream & str, bool arePaths)
 {
     StringSet res;
+    expect(str, "[");
     while (!endOfList(str))
         res.insert(arePaths ? parsePath(str) : parseString(str));
     return res;
 }
 
 
-static DerivationOutput parseDerivationOutput(const Store & store,
+static DerivationOutput parseDerivationOutput(
-    std::string_view pathS, std::string_view hashAlgo, std::string_view hashS)
+    const Store & store,
+    std::string_view pathS, std::string_view hashAlgo, std::string_view hashS,
+    const ExperimentalFeatureSettings & xpSettings)
 {
     if (hashAlgo != "") {
         ContentAddressMethod method = ContentAddressMethod::parsePrefix(hashAlgo);
         if (method == TextIngestionMethod {})
-            experimentalFeatureSettings.require(Xp::DynamicDerivations);
+            xpSettings.require(Xp::DynamicDerivations);
         const auto hashType = parseHashType(hashAlgo);
         if (hashS == "impure") {
-            experimentalFeatureSettings.require(Xp::ImpureDerivations);
+            xpSettings.require(Xp::ImpureDerivations);
-            assert(pathS == "");
+            if (pathS != "")
+                throw FormatError("impure derivation output should not specify output path");
             return DerivationOutput::Impure {
                 .method = std::move(method),
                 .hashType = std::move(hashType),
@@ -238,8 +243,9 @@ static DerivationOutput parseDerivationOutput(const Store & store,
                 },
             };
         } else {
-            experimentalFeatureSettings.require(Xp::CaDerivations);
+            xpSettings.require(Xp::CaDerivations);
-            assert(pathS == "");
+            if (pathS != "")
+                throw FormatError("content-addressed derivation output should not specify output path");
             return DerivationOutput::CAFloating {
                 .method = std::move(method),
                 .hashType = std::move(hashType),
@@ -256,29 +262,116 @@ static DerivationOutput parseDerivationOutput(const Store & store,
     }
 }
 
-static DerivationOutput parseDerivationOutput(const Store & store, std::istringstream & str)
+static DerivationOutput parseDerivationOutput(
+    const Store & store, std::istringstream & str,
+    const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings)
 {
     expect(str, ","); const auto pathS = parseString(str);
     expect(str, ","); const auto hashAlgo = parseString(str);
     expect(str, ","); const auto hash = parseString(str);
     expect(str, ")");
 
-    return parseDerivationOutput(store, pathS, hashAlgo, hash);
+    return parseDerivationOutput(store, pathS, hashAlgo, hash, xpSettings);
+}
+
+/**
+ * All ATerm Derivation format versions currently known.
+ *
+ * Unknown versions are rejected at the parsing stage.
+ */
+enum struct DerivationATermVersion {
+    /**
+     * Older unversioned form
+     */
+    Traditional,
+
+    /**
+     * Newer versioned form; only this version so far.
+     */
+    DynamicDerivations,
+};
+
+static DerivedPathMap<StringSet>::ChildNode parseDerivedPathMapNode(
+    const Store & store,
+    std::istringstream & str,
+    DerivationATermVersion version)
+{
+    DerivedPathMap<StringSet>::ChildNode node;
+
+    auto parseNonDynamic = [&]() {
+        node.value = parseStrings(str, false);
+    };
+
+    // Older derivation should never use new form, but newer
+    // derivaiton can use old form.
+    switch (version) {
+    case DerivationATermVersion::Traditional:
+        parseNonDynamic();
+        break;
+    case DerivationATermVersion::DynamicDerivations:
+        switch (str.peek()) {
+        case '[':
+            parseNonDynamic();
+            break;
+        case '(':
+            expect(str, "(");
+            node.value = parseStrings(str, false);
+            expect(str, ",[");
+            while (!endOfList(str)) {
+                expect(str, "(");
+                auto outputName = parseString(str);
+                expect(str, ",");
+                node.childMap.insert_or_assign(outputName, parseDerivedPathMapNode(store, str, version));
+                expect(str, ")");
+            }
+            expect(str, ")");
+            break;
+        default:
+            throw FormatError("invalid inputDrvs entry in derivation");
+        }
+        break;
+    default:
+        // invalid format, not a parse error but internal error
+        assert(false);
+    }
+    return node;
 }
 
 
-Derivation parseDerivation(const Store & store, std::string && s, std::string_view name)
+Derivation parseDerivation(
+    const Store & store, std::string && s, std::string_view name,
+    const ExperimentalFeatureSettings & xpSettings)
 {
     Derivation drv;
     drv.name = name;
 
     std::istringstream str(std::move(s));
-    expect(str, "Derive([");
+    expect(str, "D");
+    DerivationATermVersion version;
+    switch (str.peek()) {
+    case 'e':
+        expect(str, "erive(");
+        version = DerivationATermVersion::Traditional;
+        break;
+    case 'r':
+        expect(str, "rvWithVersion(");
+        auto versionS = parseString(str);
+        if (versionS == "xp-dyn-drv") {
+            // Only verison we have so far
+            version = DerivationATermVersion::DynamicDerivations;
+            xpSettings.require(Xp::DynamicDerivations);
+        } else {
+            throw FormatError("Unknown derivation ATerm format version '%s'", versionS);
+        }
+        expect(str, ",");
+        break;
+    }
 
     /* Parse the list of outputs. */
+    expect(str, "[");
     while (!endOfList(str)) {
         expect(str, "("); std::string id = parseString(str);
-        auto output = parseDerivationOutput(store, str);
+        auto output = parseDerivationOutput(store, str, xpSettings);
         drv.outputs.emplace(std::move(id), std::move(output));
     }
 
@@ -287,12 +380,12 @@ Derivation parseDerivation(const Store & store, std::string && s, std::string_vi
     while (!endOfList(str)) {
         expect(str, "(");
         Path drvPath = parsePath(str);
-        expect(str, ",[");
+        expect(str, ",");
-        drv.inputDrvs.insert_or_assign(store.parseStorePath(drvPath), parseStrings(str, false));
+        drv.inputDrvs.map.insert_or_assign(store.parseStorePath(drvPath), parseDerivedPathMapNode(store, str, version));
         expect(str, ")");
     }
 
-    expect(str, ",["); drv.inputSrcs = store.parseStorePathSet(parseStrings(str, true));
+    expect(str, ","); drv.inputSrcs = store.parseStorePathSet(parseStrings(str, true));
     expect(str, ","); drv.platform = parseString(str);
     expect(str, ","); drv.builder = parseString(str);
 
@@ -376,14 +469,67 @@ static void printUnquotedStrings(std::string & res, ForwardIterator i, ForwardIt
 }
 
 
+static void unparseDerivedPathMapNode(const Store & store, std::string & s, const DerivedPathMap<StringSet>::ChildNode & node)
+{
+    s += ',';
+    if (node.childMap.empty()) {
+        printUnquotedStrings(s, node.value.begin(), node.value.end());
+    } else {
+        s += "(";
+        printUnquotedStrings(s, node.value.begin(), node.value.end());
+        s += ",[";
+        bool first = true;
+        for (auto & [outputName, childNode] : node.childMap) {
+            if (first) first = false; else s += ',';
+            s += '('; printUnquotedString(s, outputName);
+            unparseDerivedPathMapNode(store, s, childNode);
+            s += ')';
+        }
+        s += "])";
+    }
+}
+
+
+/**
+ * Does the derivation have a dependency on the output of a dynamic
+ * derivation?
+ *
+ * In other words, does it on the output of derivation that is itself an
+ * ouput of a derivation? This corresponds to a dependency that is an
+ * inductive derived path with more than one layer of
+ * `DerivedPath::Built`.
+ */
+static bool hasDynamicDrvDep(const Derivation & drv)
+{
+    return
+        std::find_if(
+            drv.inputDrvs.map.begin(),
+            drv.inputDrvs.map.end(),
+            [](auto & kv) { return !kv.second.childMap.empty(); })
+        != drv.inputDrvs.map.end();
+}
+
+
 std::string Derivation::unparse(const Store & store, bool maskOutputs,
-    std::map<std::string, StringSet> * actualInputs) const
+    DerivedPathMap<StringSet>::ChildNode::Map * actualInputs) const
 {
     std::string s;
     s.reserve(65536);
-    s += "Derive([";
+
+    /* Use older unversioned form if possible, for wider compat. Use
+       newer form only if we need it, which we do for
+       `Xp::DynamicDerivations`. */
+    if (hasDynamicDrvDep(*this)) {
+        s += "DrvWithVersion(";
+        // Only version we have so far
+        printUnquotedString(s, "xp-dyn-drv");
+        s += ",";
+    } else {
+        s += "Derive(";
+    }
 
     bool first = true;
+    s += "[";
     for (auto & i : outputs) {
         if (first) first = false; else s += ',';
         s += '('; printUnquotedString(s, i.first);
@@ -421,17 +567,17 @@ std::string Derivation::unparse(const Store & store, bool maskOutputs,
     s += "],[";
     first = true;
     if (actualInputs) {
-        for (auto & i : *actualInputs) {
+        for (auto & [drvHashModulo, childMap] : *actualInputs) {
             if (first) first = false; else s += ',';
-            s += '('; printUnquotedString(s, i.first);
+            s += '('; printUnquotedString(s, drvHashModulo);
-            s += ','; printUnquotedStrings(s, i.second.begin(), i.second.end());
+            unparseDerivedPathMapNode(store, s, childMap);
             s += ')';
         }
     } else {
-        for (auto & i : inputDrvs) {
+        for (auto & [drvPath, childMap] : inputDrvs.map) {
             if (first) first = false; else s += ',';
-            s += '('; printUnquotedString(s, store.printStorePath(i.first));
+            s += '('; printUnquotedString(s, store.printStorePath(drvPath));
-            s += ','; printUnquotedStrings(s, i.second.begin(), i.second.end());
+            unparseDerivedPathMapNode(store, s, childMap);
             s += ')';
         }
     }
@@ -665,18 +811,16 @@ DrvHash hashDerivationModulo(Store & store, const Derivation & drv, bool maskOut
         }
     }, drv.type().raw);
 
-    std::map<std::string, StringSet> inputs2;
+    DerivedPathMap<StringSet>::ChildNode::Map inputs2;
-    for (auto & [drvPath, inputOutputs0] : drv.inputDrvs) {
+    for (auto & [drvPath, node] : drv.inputDrvs.map) {
-        // Avoid lambda capture restriction with standard / Clang
-        auto & inputOutputs = inputOutputs0;
         const auto & res = pathDerivationModulo(store, drvPath);
         if (res.kind == DrvHash::Kind::Deferred)
             kind = DrvHash::Kind::Deferred;
-        for (auto & outputName : inputOutputs) {
+        for (auto & outputName : node.value) {
             const auto h = get(res.hashes, outputName);
             if (!h)
                 throw Error("no hash for output '%s' of derivation '%s'", outputName, drv.name);
-            inputs2[h->to_string(Base16, false)].insert(outputName);
+            inputs2[h->to_string(Base16, false)].value.insert(outputName);
         }
     }
 
@@ -706,7 +850,7 @@ static DerivationOutput readDerivationOutput(Source & in, const Store & store)
     const auto hashAlgo = readString(in);
     const auto hash = readString(in);
 
-    return parseDerivationOutput(store, pathS, hashAlgo, hash);
+    return parseDerivationOutput(store, pathS, hashAlgo, hash, experimentalFeatureSettings);
 }
 
 StringSet BasicDerivation::outputNames() const
@@ -821,6 +965,8 @@ std::string hashPlaceholder(const OutputNameView outputName)
 
 static void rewriteDerivation(Store & store, BasicDerivation & drv, const StringMap & rewrites)
 {
+    debug("Rewriting the derivation");
+
     for (auto & rewrite : rewrites) {
         debug("rewriting %s as %s", rewrite.first, rewrite.second);
     }
@@ -859,14 +1005,70 @@ std::optional<BasicDerivation> Derivation::tryResolve(Store & store) const
 {
     std::map<std::pair<StorePath, std::string>, StorePath> inputDrvOutputs;
 
-    for (auto & input : inputDrvs)
+    std::function<void(const StorePath &, const DerivedPathMap<StringSet>::ChildNode &)> accum;
-        for (auto & [outputName, outputPath] : store.queryPartialDerivationOutputMap(input.first))
+    accum = [&](auto & inputDrv, auto & node) {
-            if (outputPath)
+        for (auto & [outputName, outputPath] : store.queryPartialDerivationOutputMap(inputDrv)) {
-                inputDrvOutputs.insert_or_assign({input.first, outputName}, *outputPath);
+            if (outputPath) {
+                inputDrvOutputs.insert_or_assign({inputDrv, outputName}, *outputPath);
+                if (auto p = get(node.childMap, outputName))
+                    accum(*outputPath, *p);
+            }
+        }
+    };
+
+    for (auto & [inputDrv, node] : inputDrvs.map)
+        accum(inputDrv, node);
 
     return tryResolve(store, inputDrvOutputs);
 }
 
+static bool tryResolveInput(
+    Store & store, StorePathSet & inputSrcs, StringMap & inputRewrites,
+    const DownstreamPlaceholder * placeholderOpt,
+    const StorePath & inputDrv, const DerivedPathMap<StringSet>::ChildNode & inputNode,
+    const std::map<std::pair<StorePath, std::string>, StorePath> & inputDrvOutputs)
+{
+    auto getOutput = [&](const std::string & outputName) {
+        auto * actualPathOpt = get(inputDrvOutputs, { inputDrv, outputName });
+        if (!actualPathOpt)
+            warn("output %s of input %s missing, aborting the resolving",
+                outputName,
+                store.printStorePath(inputDrv)
+            );
+        return actualPathOpt;
+    };
+
+    auto getPlaceholder = [&](const std::string & outputName) {
+        return placeholderOpt
+            ? DownstreamPlaceholder::unknownDerivation(*placeholderOpt, outputName)
+            : DownstreamPlaceholder::unknownCaOutput(inputDrv, outputName);
+    };
+
+    for (auto & outputName : inputNode.value) {
+        auto actualPathOpt = getOutput(outputName);
+        if (!actualPathOpt) return false;
+        auto actualPath = *actualPathOpt;
+        if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations)) {
+            inputRewrites.emplace(
+                getPlaceholder(outputName).render(),
+                store.printStorePath(actualPath));
+        }
+        inputSrcs.insert(std::move(actualPath));
+    }
+
+    for (auto & [outputName, childNode] : inputNode.childMap) {
+        auto actualPathOpt = getOutput(outputName);
+        if (!actualPathOpt) return false;
+        auto actualPath = *actualPathOpt;
+        auto nextPlaceholder = getPlaceholder(outputName);
+        if (!tryResolveInput(store, inputSrcs, inputRewrites,
+            &nextPlaceholder, actualPath, childNode,
+            inputDrvOutputs))
+            return false;
+    }
+    return true;
+}
+
 std::optional<BasicDerivation> Derivation::tryResolve(
     Store & store,
     const std::map<std::pair<StorePath, std::string>, StorePath> & inputDrvOutputs) const
@@ -876,23 +1078,10 @@ std::optional<BasicDerivation> Derivation::tryResolve(
     // Input paths that we'll want to rewrite in the derivation
     StringMap inputRewrites;
 
-    for (auto & [inputDrv, inputOutputs] : inputDrvs) {
+    for (auto & [inputDrv, inputNode] : inputDrvs.map)
-        for (auto & outputName : inputOutputs) {
+        if (!tryResolveInput(store, resolved.inputSrcs, inputRewrites,
-            if (auto actualPath = get(inputDrvOutputs, { inputDrv, outputName })) {
+            nullptr, inputDrv, inputNode, inputDrvOutputs))
-                if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations)) {
+            return std::nullopt;
-                    inputRewrites.emplace(
-                        DownstreamPlaceholder::unknownCaOutput(inputDrv, outputName).render(),
-                        store.printStorePath(*actualPath));
-                }
-                resolved.inputSrcs.insert(*actualPath);
-            } else {
-                warn("output '%s' of input '%s' missing, aborting the resolving",
-                    outputName,
-                    store.printStorePath(inputDrv));
-                return {};
-            }
-        }
-    }
 
     rewriteDerivation(store, resolved, inputRewrites);
 
@@ -1080,11 +1269,26 @@ nlohmann::json Derivation::toJSON(const Store & store) const
             inputsList.emplace_back(store.printStorePath(input));
     }
 
+    {
+        std::function<nlohmann::json(const DerivedPathMap<StringSet>::ChildNode &)> doInput;
+        doInput = [&](const auto & inputNode) {
+            auto value = nlohmann::json::object();
+            value["outputs"] = inputNode.value;
+            {
+                auto next = nlohmann::json::object();
+                for (auto & [outputId, childNode] : inputNode.childMap)
+                    next[outputId] = doInput(childNode);
+                value["dynamicOutputs"] = std::move(next);
+            }
+            return value;
+        };
         {
             auto& inputDrvsObj = res["inputDrvs"];
             inputDrvsObj = nlohmann::json::object();
-        for (auto & input : inputDrvs)
+            for (auto & [inputDrv, inputNode] : inputDrvs.map) {
-            inputDrvsObj[store.printStorePath(input.first)] = input.second;
+                inputDrvsObj[store.printStorePath(inputDrv)] = doInput(inputNode);
+            }
+        }
     }
 
     res["system"] = platform;
@@ -1098,7 +1302,8 @@ nlohmann::json Derivation::toJSON(const Store & store) const
 
 Derivation Derivation::fromJSON(
     const Store & store,
-    const nlohmann::json & json)
+    const nlohmann::json & json,
+    const ExperimentalFeatureSettings & xpSettings)
 {
     using nlohmann::detail::value_t;
 
@@ -1130,12 +1335,21 @@ Derivation Derivation::fromJSON(
     }
 
     try {
-        auto & inputDrvsObj = ensureType(valueAt(json, "inputDrvs"), value_t::object);
+        std::function<DerivedPathMap<StringSet>::ChildNode(const nlohmann::json &)> doInput;
-        for (auto & [inputDrvPath, inputOutputs] : inputDrvsObj.items()) {
+        doInput = [&](const auto & json) {
-            ensureType(inputOutputs, value_t::array);
+            DerivedPathMap<StringSet>::ChildNode node;
-            res.inputDrvs[store.parseStorePath(inputDrvPath)] =
+            node.value = static_cast<const StringSet &>(
-                static_cast<const StringSet &>(inputOutputs);
+                ensureType(valueAt(json, "outputs"), value_t::array));
+            for (auto & [outputId, childNode] : ensureType(valueAt(json, "dynamicOutputs"), value_t::object).items()) {
+                xpSettings.require(Xp::DynamicDerivations);
+                node.childMap[outputId] = doInput(childNode);
             }
+            return node;
+        };
+        auto & inputDrvsObj = ensureType(valueAt(json, "inputDrvs"), value_t::object);
+        for (auto & [inputDrvPath, inputOutputs] : inputDrvsObj.items())
+            res.inputDrvs.map[store.parseStorePath(inputDrvPath)] =
+                doInput(inputOutputs);
     } catch (Error & e) {
         e.addTrace({}, "while reading key 'inputDrvs'");
         throw;

src/libstore/derivations.hh

@@ -6,7 +6,7 @@
 #include "hash.hh"
 #include "content-address.hh"
 #include "repair-flag.hh"
-#include "derived-path.hh"
+#include "derived-path-map.hh"
 #include "sync.hh"
 #include "comparator.hh"
 #include "variant-wrapper.hh"
@@ -323,13 +323,13 @@ struct Derivation : BasicDerivation
     /**
      * inputs that are sub-derivations
      */
-    DerivationInputs inputDrvs;
+    DerivedPathMap<std::set<OutputName>> inputDrvs;
 
     /**
      * Print a derivation.
      */
     std::string unparse(const Store & store, bool maskOutputs,
-        std::map<std::string, StringSet> * actualInputs = nullptr) const;
+        DerivedPathMap<StringSet>::ChildNode::Map * actualInputs = nullptr) const;
 
     /**
      * Return the underlying basic derivation but with these changes:
@@ -368,7 +368,8 @@ struct Derivation : BasicDerivation
     nlohmann::json toJSON(const Store & store) const;
     static Derivation fromJSON(
         const Store & store,
-        const nlohmann::json & json);
+        const nlohmann::json & json,
+        const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
 
     GENERATE_CMP(Derivation,
         static_cast<const BasicDerivation &>(*me),
@@ -389,7 +390,11 @@ StorePath writeDerivation(Store & store,
 /**
  * Read a derivation from a file.
  */
-Derivation parseDerivation(const Store & store, std::string && s, std::string_view name);
+Derivation parseDerivation(
+    const Store & store,
+    std::string && s,
+    std::string_view name,
+    const ExperimentalFeatureSettings & xpSettings = experimentalFeatureSettings);
 
 /**
  * \todo Remove.

src/libstore/derived-path-map.cc

@@ -21,6 +21,32 @@ typename DerivedPathMap<V>::ChildNode & DerivedPathMap<V>::ensureSlot(const Sing
     return initIter(k);
 }
 
+template<typename V>
+typename DerivedPathMap<V>::ChildNode * DerivedPathMap<V>::findSlot(const SingleDerivedPath & k)
+{
+    std::function<ChildNode *(const SingleDerivedPath & )> initIter;
+    initIter = [&](const auto & k) {
+        return std::visit(overloaded {
+            [&](const SingleDerivedPath::Opaque & bo) {
+                auto it = map.find(bo.path);
+                return it != map.end()
+                    ? &it->second
+                    : nullptr;
+            },
+            [&](const SingleDerivedPath::Built & bfd) {
+                auto * n = initIter(*bfd.drvPath);
+                if (!n) return (ChildNode *)nullptr;
+
+                auto it = n->childMap.find(bfd.output);
+                return it != n->childMap.end()
+                    ? &it->second
+                    : nullptr;
+            },
+        }, k.raw());
+    };
+    return initIter(k);
+}
+
 }
 
 // instantiations
@@ -30,4 +56,17 @@ namespace nix {
 
 template struct DerivedPathMap<std::weak_ptr<CreateDerivationAndRealiseGoal>>;
 
-}
+GENERATE_CMP_EXT(
+    template<>,
+    DerivedPathMap<std::set<std::string>>::ChildNode,
+    me->value,
+    me->childMap);
+
+GENERATE_CMP_EXT(
+    template<>,
+    DerivedPathMap<std::set<std::string>>,
+    me->map);
+
+template struct DerivedPathMap<std::set<std::string>>;
+
+};

src/libstore/derived-path-map.hh

@@ -48,6 +48,8 @@ struct DerivedPathMap {
          * The map of the root node.
          */
         Map childMap;
+
+        DECLARE_CMP(ChildNode);
     };
 
     /**
@@ -60,6 +62,8 @@ struct DerivedPathMap {
      */
     Map map;
 
+    DECLARE_CMP(DerivedPathMap);
+
     /**
      * Find the node for `k`, creating it if needed.
      *
@@ -68,6 +72,27 @@ struct DerivedPathMap {
      * by changing this node.
      */
     ChildNode & ensureSlot(const SingleDerivedPath & k);
+
+    /**
+     * Like `ensureSlot` but does not create the slot if it doesn't exist.
+     *
+     * Read the entire description of `ensureSlot` to understand an
+     * important caveat here that "have slot" does *not* imply "key is
+     * set in map". To ensure a key is set one would need to get the
+     * child node (with `findSlot` or `ensureSlot`) *and* check the
+     * `ChildNode::value`.
+     */
+    ChildNode * findSlot(const SingleDerivedPath & k);
 };
 
+
+DECLARE_CMP_EXT(
+    template<>,
+    DerivedPathMap<std::set<std::string>>::,
+    DerivedPathMap<std::set<std::string>>);
+DECLARE_CMP_EXT(
+    template<>,
+    DerivedPathMap<std::set<std::string>>::ChildNode::,
+    DerivedPathMap<std::set<std::string>>::ChildNode);
+
 }

src/libstore/globals.hh

@@ -554,7 +554,7 @@ public:
         R"(
           This option determines the maximum size of the `tmpfs` filesystem
           mounted on `/dev/shm` in Linux sandboxes. For the format, see the
-          description of the `size` option of `tmpfs` in mount8. The default
+          description of the `size` option of `tmpfs` in mount(8). The default
           is `50%`.
         )"};
 

src/libstore/misc.cc

@@ -125,14 +125,26 @@ void Store::queryMissing(const std::vector<DerivedPath> & targets,
 
     std::function<void(DerivedPath)> doPath;
 
+    std::function<void(ref<SingleDerivedPath>, const DerivedPathMap<StringSet>::ChildNode &)> enqueueDerivedPaths;
+
+    enqueueDerivedPaths = [&](ref<SingleDerivedPath> inputDrv, const DerivedPathMap<StringSet>::ChildNode & inputNode) {
+        if (!inputNode.value.empty())
+            pool.enqueue(std::bind(doPath, DerivedPath::Built { inputDrv, inputNode.value }));
+        for (const auto & [outputName, childNode] : inputNode.childMap)
+            enqueueDerivedPaths(
+                make_ref<SingleDerivedPath>(SingleDerivedPath::Built { inputDrv, outputName }),
+                childNode);
+    };
+
     auto mustBuildDrv = [&](const StorePath & drvPath, const Derivation & drv) {
         {
             auto state(state_.lock());
             state->willBuild.insert(drvPath);
         }
 
-        for (auto & i : drv.inputDrvs)
+        for (const auto & [inputDrv, inputNode] : drv.inputDrvs.map) {
-            pool.enqueue(std::bind(doPath, DerivedPath::Built { makeConstantStorePathRef(i.first), i.second }));
+            enqueueDerivedPaths(makeConstantStorePathRef(inputDrv), inputNode);
+        }
     };
 
     auto checkOutput = [&](
@@ -322,10 +334,13 @@ std::map<DrvOutput, StorePath> drvOutputReferences(
 {
     std::set<Realisation> inputRealisations;
 
-    for (const auto & [inputDrv, outputNames] : drv.inputDrvs) {
+    std::function<void(const StorePath &, const DerivedPathMap<StringSet>::ChildNode &)> accumRealisations;
-        const auto outputHashes =
+
+    accumRealisations = [&](const StorePath & inputDrv, const DerivedPathMap<StringSet>::ChildNode & inputNode) {
+        if (!inputNode.value.empty()) {
+            auto outputHashes =
                 staticOutputHashes(store, store.readDerivation(inputDrv));
-        for (const auto & outputName : outputNames) {
+            for (const auto & outputName : inputNode.value) {
                 auto outputHash = get(outputHashes, outputName);
                 if (!outputHash)
                     throw Error(
@@ -335,11 +350,25 @@ std::map<DrvOutput, StorePath> drvOutputReferences(
                     DrvOutput{*outputHash, outputName});
                 if (!thisRealisation)
                     throw Error(
-                    "output '%s' of derivation '%s' isn't built", outputName,
+                        "output '%s' of derivation '%s' isn’t built", outputName,
                         store.printStorePath(inputDrv));
                 inputRealisations.insert(*thisRealisation);
             }
         }
+        if (!inputNode.value.empty()) {
+            auto d = makeConstantStorePathRef(inputDrv);
+            for (const auto & [outputName, childNode] : inputNode.childMap) {
+                SingleDerivedPath next = SingleDerivedPath::Built { d, outputName };
+                accumRealisations(
+                    // TODO deep resolutions for dynamic derivations, issue #8947, would go here.
+                    resolveDerivedPath(store, next),
+                    childNode);
+            }
+        }
+    };
+
+    for (const auto & [inputDrv, inputNode] : drv.inputDrvs.map)
+        accumRealisations(inputDrv, inputNode);
 
     auto info = store.queryPathInfo(outputPath);
 

src/libstore/remote-store.cc

@@ -172,7 +172,24 @@ void RemoteStore::ConnectionHandle::processStderr(Sink * sink, Source * source,
     auto ex = handle->processStderr(sink, source, flush);
     if (ex) {
         daemonException = true;
+        try {
             std::rethrow_exception(ex);
+        } catch (const Error & e) {
+            // Nix versions before #4628 did not have an adequate behavior for reporting that the derivation format was upgraded.
+            // To avoid having to add compatibility logic in many places, we expect to catch almost all occurrences of the
+            // old incomprehensible error here, so that we can explain to users what's going on when their daemon is
+            // older than #4628 (2023).
+            if (experimentalFeatureSettings.isEnabled(Xp::DynamicDerivations) &&
+                GET_PROTOCOL_MINOR(handle->daemonVersion) <= 35)
+            {
+                auto m = e.msg();
+                if (m.find("parsing derivation") != std::string::npos &&
+                    m.find("expected string") != std::string::npos &&
+                    m.find("Derive([") != std::string::npos)
+                    throw Error("%s, this might be because the daemon is too old to understand dependencies on dynamic derivations. Check to see if the raw dervation is in the form '%s'", std::move(m), "DrvWithVersion(..)");
+            }
+            throw;
+        }
     }
 }
 

src/libstore/tests/derivation.cc

@@ -42,6 +42,26 @@ class ImpureDerivationTest : public DerivationTest
     }
 };
 
+TEST_F(DerivationTest, BadATerm_version) {
+    ASSERT_THROW(
+        parseDerivation(
+            *store,
+            R"(DrvWithVersion("invalid-version",[],[("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv",["cat","dog"])],["/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"],"wasm-sel4","foo",["bar","baz"],[("BIG_BAD","WOLF")]))",
+            "whatever",
+            mockXpSettings),
+        FormatError);
+}
+
+TEST_F(DynDerivationTest, BadATerm_oldVersionDynDeps) {
+    ASSERT_THROW(
+        parseDerivation(
+            *store,
+            R"(Derive([],[("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv",(["cat","dog"],[("cat",["kitten"]),("goose",["gosling"])]))],["/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"],"wasm-sel4","foo",["bar","baz"],[("BIG_BAD","WOLF")]))",
+            "dyn-dep-derivation",
+            mockXpSettings),
+        FormatError);
+}
+
 #define TEST_JSON(FIXTURE, NAME, STR, VAL, DRV_NAME, OUTPUT_NAME) \
     TEST_F(FIXTURE, DerivationOutput_ ## NAME ## _to_json) {    \
         using nlohmann::literals::operator "" _json;           \
@@ -143,60 +163,63 @@ TEST_JSON(ImpureDerivationTest, impure,
 
 #undef TEST_JSON
 
-#define TEST_JSON(NAME, STR, VAL, DRV_NAME)                     \
+#define TEST_JSON(FIXTURE, NAME, STR, VAL)                       \
-    TEST_F(DerivationTest, Derivation_ ## NAME ## _to_json) {   \
+    TEST_F(FIXTURE, Derivation_ ## NAME ## _to_json) {           \
         using nlohmann::literals::operator "" _json;             \
         ASSERT_EQ(                                               \
             STR ## _json,                                        \
-            (Derivation { VAL }).toJSON(*store));               \
+            (VAL).toJSON(*store));                               \
     }                                                            \
                                                                  \
-    TEST_F(DerivationTest, Derivation_ ## NAME ## _from_json) { \
+    TEST_F(FIXTURE, Derivation_ ## NAME ## _from_json) {         \
         using nlohmann::literals::operator "" _json;             \
         ASSERT_EQ(                                               \
-            Derivation { VAL },                                 \
+            (VAL),                                               \
             Derivation::fromJSON(                                \
                 *store,                                          \
-                STR ## _json));                                 \
+                STR ## _json,                                    \
+                mockXpSettings));                                \
     }
 
-TEST_JSON(simple,
+#define TEST_ATERM(FIXTURE, NAME, STR, VAL, DRV_NAME)            \
-    R"({
+    TEST_F(FIXTURE, Derivation_ ## NAME ## _to_aterm) {          \
-      "name": "my-derivation",
+        ASSERT_EQ(                                               \
-      "inputSrcs": [
+            STR,                                                 \
-        "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"
+            (VAL).unparse(*store, false));                       \
-      ],
+    }                                                            \
-      "inputDrvs": {
+                                                                 \
-        "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv": [
+    TEST_F(FIXTURE, Derivation_ ## NAME ## _from_aterm) {        \
-          "cat",
+        auto parsed = parseDerivation(                           \
-          "dog"
+            *store,                                              \
-        ]
+            STR,                                                 \
-      },
+            DRV_NAME,                                            \
-      "system": "wasm-sel4",
+            mockXpSettings);                                     \
-      "builder": "foo",
+        ASSERT_EQ(                                               \
-      "args": [
+            (VAL).toJSON(*store),                                \
-        "bar",
+            parsed.toJSON(*store));                              \
-        "baz"
+        ASSERT_EQ(                                               \
-      ],
+            (VAL),                                               \
-      "env": {
+            parsed);                                             \
-        "BIG_BAD": "WOLF"
+    }
-      },
+
-      "outputs": {}
+Derivation makeSimpleDrv(const Store & store) {
-    })",
-    ({
     Derivation drv;
-        drv.name = "my-derivation";
+    drv.name = "simple-derivation";
     drv.inputSrcs = {
-            store->parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"),
+        store.parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"),
     };
     drv.inputDrvs = {
+        .map = {
             {
-                store->parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv"),
+                store.parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv"),
                 {
+                    .value = {
                         "cat",
                         "dog",
                     },
-            }
+                },
+            },
+        },
     };
     drv.platform = "wasm-sel4";
     drv.builder = "foo";
@@ -210,10 +233,137 @@ TEST_JSON(simple,
             "WOLF",
         },
     };
-        drv;
+    return drv;
-    }),
+}
-    "drv-name")
+
+TEST_JSON(DerivationTest, simple,
+    R"({
+      "name": "simple-derivation",
+      "inputSrcs": [
+        "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"
+      ],
+      "inputDrvs": {
+        "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv": {
+          "dynamicOutputs": {},
+          "outputs": [
+            "cat",
+            "dog"
+          ]
+        }
+      },
+      "system": "wasm-sel4",
+      "builder": "foo",
+      "args": [
+        "bar",
+        "baz"
+      ],
+      "env": {
+        "BIG_BAD": "WOLF"
+      },
+      "outputs": {}
+    })",
+    makeSimpleDrv(*store))
+
+TEST_ATERM(DerivationTest, simple,
+    R"(Derive([],[("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv",["cat","dog"])],["/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"],"wasm-sel4","foo",["bar","baz"],[("BIG_BAD","WOLF")]))",
+    makeSimpleDrv(*store),
+    "simple-derivation")
+
+Derivation makeDynDepDerivation(const Store & store) {
+    Derivation drv;
+    drv.name = "dyn-dep-derivation";
+    drv.inputSrcs = {
+        store.parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"),
+    };
+    drv.inputDrvs = {
+        .map = {
+            {
+                store.parseStorePath("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv"),
+                DerivedPathMap<StringSet>::ChildNode {
+                    .value = {
+                        "cat",
+                        "dog",
+                    },
+                    .childMap = {
+                        {
+                            "cat",
+                            DerivedPathMap<StringSet>::ChildNode {
+                                .value = {
+                                    "kitten",
+                                },
+                            },
+                        },
+                        {
+                            "goose",
+                            DerivedPathMap<StringSet>::ChildNode {
+                                .value = {
+                                    "gosling",
+                                },
+                            },
+                        },
+                    },
+                },
+            },
+        },
+    };
+    drv.platform = "wasm-sel4";
+    drv.builder = "foo";
+    drv.args = {
+        "bar",
+        "baz",
+    };
+    drv.env = {
+        {
+            "BIG_BAD",
+            "WOLF",
+        },
+    };
+    return drv;
+}
+
+TEST_JSON(DynDerivationTest, dynDerivationDeps,
+    R"({
+      "name": "dyn-dep-derivation",
+      "inputSrcs": [
+        "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"
+      ],
+      "inputDrvs": {
+        "/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv": {
+          "dynamicOutputs": {
+            "cat": {
+              "dynamicOutputs": {},
+              "outputs": ["kitten"]
+            },
+            "goose": {
+              "dynamicOutputs": {},
+              "outputs": ["gosling"]
+            }
+          },
+          "outputs": [
+            "cat",
+            "dog"
+          ]
+        }
+      },
+      "system": "wasm-sel4",
+      "builder": "foo",
+      "args": [
+        "bar",
+        "baz"
+      ],
+      "env": {
+        "BIG_BAD": "WOLF"
+      },
+      "outputs": {}
+    })",
+    makeDynDepDerivation(*store))
+
+TEST_ATERM(DynDerivationTest, dynDerivationDeps,
+    R"(DrvWithVersion("xp-dyn-drv",[],[("/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep2.drv",(["cat","dog"],[("cat",["kitten"]),("goose",["gosling"])]))],["/nix/store/c015dhfh5l0lp6wxyvdn7bmwhbbr6hr9-dep1"],"wasm-sel4","foo",["bar","baz"],[("BIG_BAD","WOLF")]))",
+    makeDynDepDerivation(*store),
+    "dyn-dep-derivation")
 
 #undef TEST_JSON
+#undef TEST_ATERM
 
 }

src/libutil/comparator.hh

@@ -1,21 +1,48 @@
 #pragma once
 ///@file
 
+#define DECLARE_ONE_CMP(PRE, QUAL, COMPARATOR, MY_TYPE) \
+    PRE bool QUAL operator COMPARATOR(const MY_TYPE & other) const;
+#define DECLARE_EQUAL(prefix, qualification, my_type) \
+    DECLARE_ONE_CMP(prefix, qualification, ==, my_type)
+#define DECLARE_LEQ(prefix, qualification, my_type) \
+    DECLARE_ONE_CMP(prefix, qualification, <, my_type)
+#define DECLARE_NEQ(prefix, qualification, my_type) \
+    DECLARE_ONE_CMP(prefix, qualification, !=, my_type)
+
+#define GENERATE_ONE_CMP(PRE, QUAL, COMPARATOR, MY_TYPE, ...) \
+    PRE bool QUAL operator COMPARATOR(const MY_TYPE & other) const { \
+      __VA_OPT__(const MY_TYPE * me = this;) \
+      auto fields1 = std::make_tuple( __VA_ARGS__ ); \
+      __VA_OPT__(me = &other;) \
+      auto fields2 = std::make_tuple( __VA_ARGS__ ); \
+      return fields1 COMPARATOR fields2; \
+    }
+#define GENERATE_EQUAL(prefix, qualification, my_type, args...) \
+    GENERATE_ONE_CMP(prefix, qualification, ==, my_type, args)
+#define GENERATE_LEQ(prefix, qualification, my_type, args...) \
+    GENERATE_ONE_CMP(prefix, qualification, <, my_type, args)
+#define GENERATE_NEQ(prefix, qualification, my_type, args...) \
+    GENERATE_ONE_CMP(prefix, qualification, !=, my_type, args)
+
 /**
  * Declare comparison methods without defining them.
  */
-#define DECLARE_ONE_CMP(COMPARATOR, MY_TYPE) \
-    bool operator COMPARATOR(const MY_TYPE & other) const;
-#define DECLARE_EQUAL(my_type) \
-    DECLARE_ONE_CMP(==, my_type)
-#define DECLARE_LEQ(my_type) \
-    DECLARE_ONE_CMP(<, my_type)
-#define DECLARE_NEQ(my_type) \
-    DECLARE_ONE_CMP(!=, my_type)
 #define DECLARE_CMP(my_type) \
-    DECLARE_EQUAL(my_type) \
+    DECLARE_EQUAL(,,my_type) \
-    DECLARE_LEQ(my_type) \
+    DECLARE_LEQ(,,my_type) \
-    DECLARE_NEQ(my_type)
+    DECLARE_NEQ(,,my_type)
+
+/**
+ * @param prefix This is for something before each declaration like
+ * `template<classname Foo>`.
+ *
+ * @param my_type the type are defining operators for.
+ */
+#define DECLARE_CMP_EXT(prefix, qualification, my_type) \
+    DECLARE_EQUAL(prefix, qualification, my_type) \
+    DECLARE_LEQ(prefix, qualification, my_type) \
+    DECLARE_NEQ(prefix, qualification, my_type)
 
 /**
  * Awful hacky generation of the comparison operators by doing a lexicographic
@@ -33,18 +60,18 @@
  * }
  * ```
  */
-#define GENERATE_ONE_CMP(COMPARATOR, MY_TYPE, ...) \
-    bool operator COMPARATOR(const MY_TYPE& other) const { \
-      __VA_OPT__(const MY_TYPE* me = this;) \
-      auto fields1 = std::make_tuple( __VA_ARGS__ ); \
-      __VA_OPT__(me = &other;) \
-      auto fields2 = std::make_tuple( __VA_ARGS__ ); \
-      return fields1 COMPARATOR fields2; \
-    }
-#define GENERATE_EQUAL(args...) GENERATE_ONE_CMP(==, args)
-#define GENERATE_LEQ(args...) GENERATE_ONE_CMP(<, args)
-#define GENERATE_NEQ(args...) GENERATE_ONE_CMP(!=, args)
 #define GENERATE_CMP(args...) \
-    GENERATE_EQUAL(args) \
+    GENERATE_EQUAL(,,args) \
-    GENERATE_LEQ(args) \
+    GENERATE_LEQ(,,args) \
-    GENERATE_NEQ(args)
+    GENERATE_NEQ(,,args)
+
+/**
+ * @param prefix This is for something before each declaration like
+ * `template<classname Foo>`.
+ *
+ * @param my_type the type are defining operators for.
+ */
+#define GENERATE_CMP_EXT(prefix, my_type, args...) \
+    GENERATE_EQUAL(prefix, my_type ::, my_type, args) \
+    GENERATE_LEQ(prefix, my_type ::, my_type, args) \
+    GENERATE_NEQ(prefix, my_type ::, my_type, args)

src/libutil/logging.cc

@@ -220,8 +220,8 @@ struct JSONLogger : Logger {
         json["level"] = lvl;
         json["type"] = type;
         json["text"] = s;
+        json["parent"] = parent;
         addFields(json, fields);
-        // FIXME: handle parent
         write(json);
     }
 

src/libutil/util.cc

@@ -60,7 +60,7 @@ void initLibUtil() {
     bool caught = false;
     try {
         throwExceptionSelfCheck();
-    } catch (nix::Error _e) {
+    } catch (const nix::Error & _e) {
         caught = true;
     }
     // This is not actually the main point of this check, but let's make sure anyway:

src/nix-build/nix-build.cc

@@ -406,8 +406,22 @@ static void main_nix_build(int argc, char * * argv)
             }
         }
 
+        std::function<void(ref<SingleDerivedPath>, const DerivedPathMap<StringSet>::ChildNode &)> accumDerivedPath;
+
+        accumDerivedPath = [&](ref<SingleDerivedPath> inputDrv, const DerivedPathMap<StringSet>::ChildNode & inputNode) {
+            if (!inputNode.value.empty())
+                pathsToBuild.push_back(DerivedPath::Built {
+                    .drvPath = inputDrv,
+                    .outputs = OutputsSpec::Names { inputNode.value },
+                });
+            for (const auto & [outputName, childNode] : inputNode.childMap)
+                accumDerivedPath(
+                    make_ref<SingleDerivedPath>(SingleDerivedPath::Built { inputDrv, outputName }),
+                    childNode);
+        };
+
         // Build or fetch all dependencies of the derivation.
-        for (const auto & [inputDrv0, inputOutputs] : drv.inputDrvs) {
+        for (const auto & [inputDrv0, inputNode] : drv.inputDrvs.map) {
             // To get around lambda capturing restrictions in the
             // standard.
             const auto & inputDrv = inputDrv0;
@@ -416,10 +430,7 @@ static void main_nix_build(int argc, char * * argv)
                         return !std::regex_search(store->printStorePath(inputDrv), std::regex(exclude));
                     }))
             {
-                pathsToBuild.push_back(DerivedPath::Built {
+                accumDerivedPath(makeConstantStorePathRef(inputDrv), inputNode);
-                    .drvPath = makeConstantStorePathRef(inputDrv),
-                    .outputs = OutputsSpec::Names { inputOutputs },
-                });
                 pathsToCopy.insert(inputDrv);
             }
         }
@@ -482,13 +493,21 @@ static void main_nix_build(int argc, char * * argv)
 
         if (env.count("__json")) {
             StorePathSet inputs;
-            for (auto & [depDrvPath, wantedDepOutputs] : drv.inputDrvs) {
+
-                auto outputs = evalStore->queryPartialDerivationOutputMap(depDrvPath);
+            std::function<void(const StorePath &, const DerivedPathMap<StringSet>::ChildNode &)> accumInputClosure;
-                for (auto & i : wantedDepOutputs) {
+
+            accumInputClosure = [&](const StorePath & inputDrv, const DerivedPathMap<StringSet>::ChildNode & inputNode) {
+                auto outputs = evalStore->queryPartialDerivationOutputMap(inputDrv);
+                for (auto & i : inputNode.value) {
                     auto o = outputs.at(i);
                     store->computeFSClosure(*o, inputs);
                 }
-            }
+                for (const auto & [outputName, childNode] : inputNode.childMap)
+                    accumInputClosure(*outputs.at(outputName), childNode);
+            };
+
+            for (const auto & [inputDrv, inputNode] : drv.inputDrvs.map)
+                accumInputClosure(inputDrv, inputNode);
 
             ParsedDerivation parsedDrv(drvInfo.requireDrvPath(), drv);
 

src/nix-store/nix-store.cc

@@ -283,7 +283,7 @@ static void opQuery(Strings opFlags, Strings opArgs)
 {
     enum QueryType
         { qOutputs, qRequisites, qReferences, qReferrers
-        , qReferrersClosure, qDeriver, qBinding, qHash, qSize
+        , qReferrersClosure, qDeriver, qValidDerivers, qBinding, qHash, qSize
         , qTree, qGraph, qGraphML, qResolve, qRoots };
     std::optional<QueryType> query;
     bool useOutput = false;
@@ -299,6 +299,7 @@ static void opQuery(Strings opFlags, Strings opArgs)
         else if (i == "--referrers" || i == "--referers") query = qReferrers;
         else if (i == "--referrers-closure" || i == "--referers-closure") query = qReferrersClosure;
         else if (i == "--deriver" || i == "-d") query = qDeriver;
+        else if (i == "--valid-derivers") query = qValidDerivers;
         else if (i == "--binding" || i == "-b") {
             if (opArgs.size() == 0)
                 throw UsageError("expected binding name");
@@ -372,6 +373,21 @@ static void opQuery(Strings opFlags, Strings opArgs)
             }
             break;
 
+        case qValidDerivers: {
+            StorePathSet result;
+            for (auto & i : opArgs) {
+                auto derivers = store->queryValidDerivers(store->followLinksToStorePath(i));
+                for (const auto &i: derivers) {
+                    result.insert(i);
+                }
+            }
+            auto sorted = store->topoSortPaths(result);
+            for (StorePaths::reverse_iterator i = sorted.rbegin();
+                 i != sorted.rend(); ++i)
+                cout << fmt("%s\n", store->printStorePath(*i));
+            break;
+        }
+
         case qBinding:
             for (auto & i : opArgs) {
                 auto path = useDeriver(store->followLinksToStorePath(i));

src/nix/app.cc

@@ -20,15 +20,22 @@ StringPairs resolveRewrites(
     const std::vector<BuiltPathWithResult> & dependencies)
 {
     StringPairs res;
-    for (auto & dep : dependencies)
+    if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations)) {
-        if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep.path))
+        for (auto & dep : dependencies) {
-            if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations))
+            if (auto drvDep = std::get_if<BuiltPathBuilt>(&dep.path)) {
-                for (auto & [ outputName, outputPath ] : drvDep->outputs)
+                for (auto & [ outputName, outputPath ] : drvDep->outputs) {
                     res.emplace(
-                        DownstreamPlaceholder::unknownCaOutput(
+                        DownstreamPlaceholder::fromSingleDerivedPathBuilt(
-                            drvDep->drvPath->outPath(), outputName).render(),
+                            SingleDerivedPath::Built {
+                                .drvPath = make_ref<SingleDerivedPath>(drvDep->drvPath->discardOutputPath()),
+                                .output = outputName,
+                            }).render(),
                         store.printStorePath(outputPath)
                     );
+                }
+            }
+        }
+    }
     return res;
 }
 

src/nix/develop.md

@@ -69,7 +69,7 @@ R""(
 * Run a series of script commands:
 
   ```console
-  # nix develop --command bash --command "mkdir build && cmake .. && make"
+  # nix develop --command bash -c "mkdir build && cmake .. && make"
   ```
 
 # Description

src/nix/shell.md

@@ -26,7 +26,7 @@ R""(
 * Run multiple commands in a shell environment:
 
   ```console
-  # nix shell nixpkgs#gnumake --command sh --command "cd src && make"
+  # nix shell nixpkgs#gnumake --command sh -c "cd src && make"
   ```
 
 * Run GNU Hello in a chroot store:

tests/check-refs.nix

@@ -2,7 +2,7 @@ with import ./config.nix;
 
 rec {
 
-  dep = import ./dependencies.nix;
+  dep = import ./dependencies.nix {};
 
   makeTest = nr: args: mkDerivation ({
     name = "check-refs-" + toString nr;

tests/dependencies.nix

@@ -1,3 +1,4 @@
+{ hashInvalidator ? "" }:
 with import ./config.nix;
 
 let {
@@ -21,6 +22,17 @@ let {
     '';
   };
 
+  fod_input = mkDerivation {
+    name = "fod-input";
+    buildCommand = ''
+      echo ${hashInvalidator}
+      echo FOD > $out
+    '';
+    outputHashMode = "flat";
+    outputHashAlgo = "sha256";
+    outputHash = "1dq9p0hnm1y75q2x40fws5887bq1r840hzdxak0a9djbwvx0b16d";
+  };
+
   body = mkDerivation {
     name = "dependencies-top";
     builder = ./dependencies.builder0.sh + "/FOOBAR/../.";
@@ -29,6 +41,7 @@ let {
     input1_drv = input1;
     input2_drv = input2;
     input0_drv = input0;
+    fod_input_drv = fod_input;
     meta.description = "Random test package";
   };
 

tests/dependencies.sh

@@ -53,3 +53,20 @@ nix-store -q --referrers-closure "$input2OutPath" | grep "$outPath"
 # Check that the derivers are set properly.
 test $(nix-store -q --deriver "$outPath") = "$drvPath"
 nix-store -q --deriver "$input2OutPath" | grepQuiet -- "-input-2.drv"
+
+# --valid-derivers returns the currently single valid .drv file
+test "$(nix-store -q --valid-derivers "$outPath")" = "$drvPath"
+
+# instantiate a different drv with the same output
+drvPath2=$(nix-instantiate dependencies.nix --argstr hashInvalidator yay)
+
+# now --valid-derivers returns both
+test "$(nix-store -q --valid-derivers "$outPath" | sort)" = "$(sort <<< "$drvPath"$'\n'"$drvPath2")"
+
+# check that nix-store --valid-derivers only returns existing drv
+nix-store --delete "$drvPath"
+test "$(nix-store -q --valid-derivers "$outPath")" = "$drvPath2"
+
+# check that --valid-derivers returns nothing when there are no valid derivers
+nix-store --delete "$drvPath2"
+test -z "$(nix-store -q --valid-derivers "$outPath")"

tests/dyn-drv/dep-built-drv.sh

@@ -6,4 +6,6 @@ out1=$(nix-build ./text-hashed-output.nix -A hello --no-out-link)
 
 clearStore
 
-expectStderr 1 nix-build ./text-hashed-output.nix -A wrapper --no-out-link | grepQuiet "Dependencies on the outputs of dynamic derivations are not yet supported"
+out2=$(nix-build ./text-hashed-output.nix -A wrapper --no-out-link)
+
+diff -r $out1 $out2

tests/dyn-drv/eval-outputOf.sh

@@ -13,14 +13,14 @@ nix --experimental-features 'nix-command' eval --impure  --expr \
 # the future so it does work, but there are some design questions to
 # resolve first. Adding a test so we don't liberalise it by accident.
 expectStderr 1 nix --experimental-features 'nix-command dynamic-derivations' eval --impure --expr \
-    'builtins.outputOf (import ../dependencies.nix) "out"' \
+    'builtins.outputOf (import ../dependencies.nix {}) "out"' \
     | grepQuiet "value is a set while a string was expected"
 
 # Test that "DrvDeep" string contexts are not supported at this time
 #
 # Like the above, this is a restriction we could relax later.
 expectStderr 1 nix --experimental-features 'nix-command dynamic-derivations' eval --impure --expr \
-    'builtins.outputOf (import ../dependencies.nix).drvPath "out"' \
+    'builtins.outputOf (import ../dependencies.nix {}).drvPath "out"' \
     | grepQuiet "has a context which refers to a complete source and binary closure. This is not supported at this time"
 
 # Test using `builtins.outputOf` with static derivations

tests/dyn-drv/local.mk

@@ -3,7 +3,8 @@ dyn-drv-tests := \
   $(d)/recursive-mod-json.sh \
   $(d)/build-built-drv.sh \
   $(d)/eval-outputOf.sh \
-  $(d)/dep-built-drv.sh
+  $(d)/dep-built-drv.sh \
+  $(d)/old-daemon-error-hack.sh
 
 install-tests-groups += dyn-drv
 

tests/dyn-drv/old-daemon-error-hack.nix

@@ -0,0 +1,20 @@
+with import ./config.nix;
+
+# A simple content-addressed derivation.
+# The derivation can be arbitrarily modified by passing a different `seed`,
+# but the output will always be the same
+rec {
+  stub = mkDerivation {
+    name = "stub";
+    buildCommand = ''
+      echo stub > $out
+    '';
+  };
+  wrapper = mkDerivation {
+    name = "has-dynamic-drv-dep";
+    buildCommand = ''
+      exit 1 # we're not building this derivation
+      ${builtins.outputOf stub.outPath "out"}
+    '';
+  };
+}

tests/dyn-drv/old-daemon-error-hack.sh

@@ -0,0 +1,11 @@
+# Purposely bypassing our usual common for this subgroup
+source ../common.sh
+
+# Need backend to support text-hashing too
+isDaemonNewer "2.18.0pre20230906" && skipTest "Daemon is too new"
+
+enableFeatures "ca-derivations dynamic-derivations"
+
+restartDaemon
+
+expectStderr 1 nix-instantiate --read-write-mode ./old-daemon-error-hack.nix | grepQuiet "the daemon is too old to understand dependencies on dynamic derivations"

tests/export-graph.nix

@@ -17,13 +17,13 @@ rec {
   foo."bar.runtimeGraph" = mkDerivation {
     name = "dependencies";
     builder = builtins.toFile "build-graph-builder" "${printRefs}";
-    exportReferencesGraph = ["refs" (import ./dependencies.nix)];
+    exportReferencesGraph = ["refs" (import ./dependencies.nix {})];
   };
 
   foo."bar.buildGraph" = mkDerivation {
     name = "dependencies";
     builder = builtins.toFile "build-graph-builder" "${printRefs}";
-    exportReferencesGraph = ["refs" (import ./dependencies.nix).drvPath];
+    exportReferencesGraph = ["refs" (import ./dependencies.nix {}).drvPath];
   };
 
 }

tests/lang/eval-okay-pathexists.nix

@@ -1,4 +1,7 @@
-builtins.pathExists (builtins.toPath ./lib.nix)
+builtins.pathExists (./lib.nix)
+&& builtins.pathExists (builtins.toPath ./lib.nix)
+&& builtins.pathExists (builtins.toString ./lib.nix)
+&& !builtins.pathExists (builtins.toString ./lib.nix + "/")
 && builtins.pathExists (builtins.toPath (builtins.toString ./lib.nix))
 && !builtins.pathExists (builtins.toPath (builtins.toString ./bla.nix))
 && builtins.pathExists ./lib.nix

tests/remote-store.sh

@@ -24,7 +24,7 @@ fi
   import (
     mkDerivation {
       name = "foo";
-      bla = import ./dependencies.nix;
+      bla = import ./dependencies.nix {};
       buildCommand = "
         echo \\\"hi\\\" > $out
       ";