Release notes

doc/manual/src/release-notes/rl-2.4.md

@@ -1,8 +1,492 @@
-# Release 2.4 (202X-XX-XX)
+# Release 2.4 (2021-10-XX)
 
-  - It is now an error to modify the `plugin-files` setting via a
-    command-line flag that appears after the first non-flag argument
-    to any command, including a subcommand to `nix`. For example,
+This is the first release in more than two years and is the result of
+more than 2800 commits from 195 contributors since release 2.3.
+
+## Highlights
+
+* Nix's **error messages** have been improved a lot. For instance,
+  evaluation errors now point out the location of the error:
+
+  ```
+  $ nix build
+  error: undefined variable 'bzip3'
+
+         at /nix/store/449lv242z0zsgwv95a8124xi11sp419f-source/flake.nix:88:13:
+
+             87|           [ curl
+             88|             bzip3 xz brotli editline
+               |             ^
+             89|             openssl sqlite
+  ```
+
+* The **`nix` command** has seen a lot of work and is now almost at
+  feature parity with the old command-line interface (the `nix-*`
+  commands). It aims to be [more modern, consistent and pleasant to
+  use](../contributing/cli-guideline.md) than the old CLI.
+
+* **Flakes** are a new format to package Nix-based projects in a more
+  discoverable, composable, consistent and reproducible way. A flake
+  is just a repository or tarball containing a file named `flake.nix`
+  that specifies dependencies on other flakes and returns any Nix
+  assets such as packages, Nixpkgs overlays, NixOS modules or CI
+  tests. The new `nix` CLI is primarily based around flakes; for
+  example, a command like `nix run nixpkgs#hello` runs the `hello`
+  application from the `nixpkgs` flake.
+
+  Flakes are currently marked as experimental. For an introduction,
+  see [this blog
+  post](https://www.tweag.io/blog/2020-05-25-flakes/). For detailed
+  information about flake syntax and semantics, see the [`nix flake`
+  manual page](../command-ref/new-cli/nix3-flake.md).
+
+* Nix's store can now be **content-addressed**, meaning that the hash
+  component of a store path is the hash of the path's
+  contents. Previously Nix could only build **input-addressed** store
+  paths, where the hash is computed from the derivation dependency
+  graph. Content-addressing allows deduplication, early cutoff in
+  build systems, and unpriviliged closure copying. This is still [an
+  experimental
+  feature](https://discourse.nixos.org/t/content-addressed-nix-call-for-testers/12881).
+
+* The Nix manual has been converted into Markdown, making it easier to
+  contribute. In addition, every `nix` subcommand now has a manual
+  page, documenting every option.
+
+* A new setting that allows **experimental features** to be enabled
+  selectively. This allows us to merge unstable features into Nix more
+  quickly and do more frequent releases.
+
+## Other features
+
+* There are many new `nix` subcommands:
+
+  - `nix develop` is intended to replace `nix-shell`. It has a number
+    of new features:
+
+    * It automatically sets the output environment variables (such as
+      `$out`) to writable locations (such as `./outputs/out`).
+
+    * It can store the environment in a profile. This is useful for
+      offline work.
+
+    * It can run specific phases directly. For instance, `nix develop
+      --build` runs `buildPhase`.
+
+    - It allows dependencies in the Nix store to be "redirected" to
+      arbitrary directories using the `--redirect` flag. This is
+      useful if you want to hack on a package *and* some of its
+      dependencies at the same time.
+
+  - `nix print-dev-env` prints the environment variables and bash
+    functions defined by a derivation. This is useful for users of
+    other shells than bash (especially with `--json`).
+
+  - `nix shell` was previously named `nix run` and is intended to
+    replace `nix-shell -p`, but without the `stdenv` overhead. It
+    simply starts a shell where some packages have been added to
+    `$PATH`.
+
+  - `nix run` (not to be confused with the old subcommand that has
+    been renamed to `nix shell`) runs an "app", a flake output that
+    specifies a command to run, or an eponymous program from a
+    package. For example, `nix run nixpkgs#hello` runs the `hello`
+    program from the `hello` package in `nixpkgs`.
+
+  - `nix flake` is the container for flake-related operations, such as
+    creating a new flake, quering the contents of a flake or updating
+    flake lock files.
+
+  - `nix registry` allows you to query and update the flake registry,
+    which maps identifiers such as `nixpkgs` to concrete flake URLs.
+
+  - `nix profile` is intended to replace `nix-env`. Its main advantage
+    is that it keeps track of the provenance of installed packages
+    (e.g. exactly which flake version a package came from). It also
+    has some helpful subcommands:
+
+    * `nix profile history` shows what packages were added, upgraded
+      or removed between each version of a profile.
+
+    * `nix profile diff-closures` shows the changes between the
+      closures of each version of a profile. This allows you to
+      discover the addition or removal of dependencies or size
+      changes.
+
+    **Warning**: after a profile has been updated using `nix profile`,
+    it is no longer useable with `nix-env`.
+
+  - `nix store diff-closures` shows the differences between the
+    closures of two store paths in terms of the versions and sizes of
+    dependencies in the closures.
+
+  - `nix store make-content-addressable` rewrites an arbitrary closure
+    to make it content-addressed. Such paths can be copied into other
+    stores without requiring signatures.
+
+  - `nix bundle` uses the [`nix-bundle`
+    program](https://github.com/matthewbauer/nix-bundle) to convert a
+    closure into a self-extracting executable.
+
+  - Various other replacements for the old CLI, e.g. `nix store gc`,
+    `nix store delete`, `nix store repair`, `nix nar dump-path`, `nix
+    store prefetch-file`, `nix store prefetch-tarball`, `nix key` and
+    `nix daemon`.
+
+* Nix now has an **evaluation cache** for flake outputs. For example,
+  a second invocation of the command `nix run nixpkgs#firefox` will
+  not need to evaluate the `firefox` attribute because it's already in
+  the evaluation cache. This is made possible by the hermetic
+  evaluation model of flakes.
+
+* The new `--offline` flag disables substituters and causes all
+  locally cached tarballs and repositories to be considered
+  up-to-date.
+
+* The new `--refresh` flag causes all locally cached tarballs and
+  repositories to be considered out-of-date.
+
+* Many `nix` subcommands now have a `--json` option to produce
+  machine-readable output.
+
+* `nix repl` has a new `:doc` command to show documentation about
+  builtin functions (e.g. `:doc builtins.map`).
+
+* Binary cache stores now have an option `index-debug-info` to create
+  an index of DWARF debuginfo files for use by
+  [`dwarffs`](https://github.com/edolstra/dwarffs).
+
+* To support flakes, Nix now has an extensible mechanism for fetching
+  source trees. Currently it has the following backends:
+
+  * Git repositories
+
+  * Mercurial repositories
+
+  * GitHub and GitLab repositories (an optimisation for faster
+    fetching than Git)
+
+  * Tarballs
+
+  * Arbitrary directories
+
+  The fetcher infrastructure is exposed via flake input specifications
+  and via the `fetchTree` built-in.
+
+* **Languages changes**: the only new language feature is that you can
+  now have antiquotations in paths, e.g. `./${foo}` instead of `./. +
+  foo`.
+
+* **New built-in functions**:
+
+  - `builtins.fetchTree` allows fetching a source tree using any
+    backends supported by the fetcher infrastructure. It replaces
+    `fetchGit`, `fetchMercurial` and `fetchTarball`.
+
+  - `builtins.getFlake` fetches a flake and returns its output
+    attributes. This function should not be used inside flakes! Use
+    flake inputs instead.
+
+  - `builtins.floor` and `builtins.ceil` round a floating-point number
+    down and up, respectively.
+
+* Experimental support for recursive Nix. This means that Nix
+  derivations can now call Nix to build other derivations. This is not
+  in a stable state yet and not well
+  [documented](https://github.com/NixOS/nix/commit/c4d7c76b641d82b2696fef73ce0ac160043c18da).
+
+* The new experimental feature `no-url-literals` disables URL
+  literals. This helps to implement [RFC
+  45](https://github.com/NixOS/rfcs/pull/45).
+
+* Nix now uses `libarchive` to decompress and unpack tarballs and zip
+  files, so `tar` is no longer required.
+
+* The priority of substituters can now be overriden using the
+  `priority` substituter setting (e.g. `--substituters
+  'http://cache.nixos.org?priority=100 daemon?priority=10'`).
+
+* `nix edit` now supports non-derivation attributes, e.g. `nix edit
+  .#nixosConfigurations.bla`.
+
+* The `nix` command now provides command line completion for `bash`,
+  `zsh` and `fish`. Since the support for getting completions is built
+  into `nix`, it's easy to add support for other shells.
+
+* The new `--log-format` flag selects what Nix's output looks like. It
+  defaults to a terse progress indicator. There is a new
+  `internal-json` output format for use by other programs.
+
+* `nix eval` has a new `--apply` flag that applies a function to the
+  evaluation result.
+
+* `nix eval` has a new `--write-to` flag that allows it to write a
+  nested attribute set of string leaves to a correspondingly directory
+  tree.
+
+* Memory improvements: many operations that add paths to the store or
+  copy paths between stores now run in constant memory.
+
+* Many `nix` commands now support the flag `--derivation` to operate
+  on a `.drv` file itself instead of its outputs.
+
+* There is a new store called `dummy://` that does not support
+  building or adding paths. This is useful if you want to use the Nix
+  evaluator but don't have a Nix store.
+
+* The `ssh-ng://` store now allows substituting paths on the remote,
+  as `ssh://` already did.
+
+* When auto-calling a function with an ellipsis, all arguments are now
+  passed.
+
+* New `nix-shell` features:
+
+  - It preserves the `PS1` environment variable if
+    `NIX_SHELL_PRESERVE_PROMPT` is set.
+
+  - With `-p`, it passes any `--arg`s as Nixpkgs arguments.
+
+* `nix-prefetch-url` has a new `--executable` flag.
+
+* On `x86_64` systems, [`x86_64` microarchitecture
+  levels](https://lwn.net/Articles/844831/) are mapped to additional
+  system types (e.g. `x86_64-v1-linux`).
+
+* The new `--eval-store` flag allows you to use a different store for
+  evaluation than for building or storing the build result. This is
+  primarily useful when you want to query whether something exists in
+  a read-only store, such as a binary cache:
+
+  ```
+  # nix path-info --json --store https://cache.nixos.org \
+    --eval-store auto nixpkgs#hello
+  ```
+
+  (Here `auto` indicates the local store.)
+
+* The Nix daemon has a new low-latency mechanism for copying
+  closures. This is useful when building on remote stores such as
+  `ssh-ng://`.
+
+* Plugins can now register `nix` subcommands.
+
+## Incompatible changes
+
+* The `nix` command is now marked as an experimental feature. This
+  means that you need to add
+
+  > experimental-features = nix-command
+
+  to your `nix.conf` if you want to use it, or pass
+  `--extra-experimental-features nix-command` on the command line.
+
+* `nix run` has been renamed to `nix shell`.
+
+* It is now an error to modify the `plugin-files` setting via a
+  command-line flag that appears after the first non-flag argument to
+  any command, including a subcommand to `nix`. For example,
   `nix-instantiate default.nix --plugin-files ""` must now become
   `nix-instantiate --plugin-files "" default.nix`.
-  - Plugins that add new `nix` subcommands are now actually respected.
+
+* We no longer release source tarballs. If you want to build from
+  source, please build from the Git repository.
+
+## Contributors
+
+This release has contributions from
+Adam Höse,
+Albert Safin,
+Alex Kovar,
+Alex Zero,
+Alexander Bantyev,
+Alexandre Esteves,
+Alyssa Ross,
+Anatole Lucet,
+Anders Kaseorg,
+Andreas Rammhold,
+Antoine Eiche,
+Antoine Martin,
+Arnout Engelen,
+Arthur Gautier,
+aszlig,
+Ben Burdette,
+Benjamin Hipple,
+Bernardo Meurer,
+Björn Gohla,
+Bjørn Forsman,
+Bob van der Linden,
+Brian Leung,
+Brian McKenna,
+Brian Wignall,
+Bruce Toll,
+Bryan Richter,
+Calle Rosenquist,
+Calvin Loncaric,
+Carlo Nucera,
+Carlos D'Agostino,
+Chaz Schlarp,
+Christian Höppner,
+Christian Kampka,
+Chua Hou,
+Chuck,
+Cole Helbling,
+Daiderd Jordan,
+Dan Callahan,
+Dani,
+Daniel Fitzpatrick,
+Danila Fedorin,
+Daniël de Kok,
+Danny Bautista,
+DavHau,
+David McFarland,
+Dima,
+Domen Kožar,
+Dominik Schrempf,
+Dominique Martinet,
+dramforever,
+Dustin DeWeese,
+edef,
+Eelco Dolstra,
+Emilio Karakey,
+Emily,
+Eric Culp,
+Ersin Akinci,
+Fabian Möller,
+Farid Zakaria,
+Federico Pellegrin,
+Finn Behrens,
+Florian Franzen,
+Félix Baylac-Jacqué,
+Gabriel Gonzalez,
+Geoff Reedy,
+Georges Dubus,
+Graham Christensen,
+Greg Hale,
+Greg Price,
+Gregor Kleen,
+Gregory Hale,
+Griffin Smith,
+Guillaume Bouchard,
+Harald van Dijk,
+illustris,
+Ivan Zvonimir Horvat,
+Jade,
+Jake Waksbaum,
+jakobrs,
+James Ottaway,
+Jan Tojnar,
+Janne Heß,
+Jaroslavas Pocepko,
+Jarrett Keifer,
+Jeremy Schlatter,
+Joachim Breitner,
+Joe Hermaszewski,
+Joe Pea,
+John Ericson,
+Jonathan Ringer,
+Josef Kemetmüller,
+Joseph Lucas,
+Jude Taylor,
+Julian Stecklina,
+Julien Tanguy,
+Jörg Thalheim,
+Kai Wohlfahrt,
+keke,
+Keshav Kini,
+Kevin Quick,
+Kevin Stock,
+Kjetil Orbekk,
+Krzysztof Gogolewski,
+kvtb,
+Lars Mühmel,
+Leonhard Markert,
+Lily Ballard,
+Linus Heckemann,
+Lorenzo Manacorda,
+Lucas Desgouilles,
+Lucas Franceschino,
+Lucas Hoffmann,
+Luke Granger-Brown,
+Madeline Haraj,
+Marwan Aljubeh,
+Mat Marini,
+Mateusz Piotrowski,
+Matthew Bauer,
+Matthew Kenigsberg,
+Mauricio Scheffer,
+Maximilian Bosch,
+Michael Adler,
+Michael Bishop,
+Michael Fellinger,
+Michael Forney,
+Michael Reilly,
+mlatus,
+Mykola Orliuk,
+Nathan van Doorn,
+Naïm Favier,
+ng0,
+Nick Van den Broeck,
+Nicolas Stig124 Formichella,
+Niels Egberts,
+Niklas Hambüchen,
+Nikola Knezevic,
+oxalica,
+p01arst0rm,
+Pamplemousse,
+Patrick Hilhorst,
+Paul Opiyo,
+Pavol Rusnak,
+Peter Kolloch,
+Philipp Bartsch,
+Philipp Middendorf,
+Piotr Szubiakowski,
+Profpatsch,
+Puck Meerburg,
+Ricardo M. Correia,
+Rickard Nilsson,
+Robert Hensing,
+Robin Gloster,
+Rodrigo,
+Rok Garbas,
+Ronnie Ebrin,
+Rovanion Luckey,
+Ryan Burns,
+Ryan Mulligan,
+Ryne Everett,
+Sam Doshi,
+Sam Lidder,
+Samir Talwar,
+Samuel Dionne-Riel,
+Sebastian Ullrich,
+Sergei Trofimovich,
+Sevan Janiyan,
+Shao Cheng,
+Shea Levy,
+Silvan Mosberger,
+Stefan Frijters,
+Stefan Jaax,
+sternenseemann,
+Steven Shaw,
+Stéphan Kochen,
+SuperSandro2000,
+Suraj Barkale,
+Taeer Bar-Yam,
+Thomas Churchman,
+Théophane Hufschmitt,
+Timothy DeHerrera,
+Timothy Klim,
+Tobias Möst,
+Tobias Pflug,
+Tom Bereknyei,
+Travis A. Everett,
+Ujjwal Jain,
+Vladimír Čunát,
+Wil Taylor,
+Will Dietz,
+Yaroslav Bolyukin,
+Yestin L. Harrison,
+YI,
+Yorick van Pelt,
+Yuriy Taraday and
+zimbatm.