Commit graph

266 commits

Author SHA1 Message Date
Ben Burdette e6f93b94fc Merge branch 'master' into caveman-LOCs 2020-06-18 13:07:53 -06:00
Eelco Dolstra 2a61bbf77f Some backports from the flakes branch 2020-06-18 14:03:00 +02:00
Matthew Bauer f767bedfac Replace struct StorePath with class StorePath
also a similar case with struct Goal
2020-06-17 13:26:37 -04:00
Ben Burdette 6a420d672c print LOC for stdin, string args 2020-05-20 22:18:26 -06:00
Eelco Dolstra b4e23dcd9e nix search: Search legacyPackages recursively 2020-04-27 16:29:26 +02:00
Eelco Dolstra aaa109565e Use a more space/time-efficient representation for the eval cache 2020-04-17 23:04:21 +02:00
Eelco Dolstra 0a10854f85 Misc changes from the flakes branch 2020-03-24 14:34:47 +01:00
Eelco Dolstra c34a20e1f6 EvalState::allocAttr(): Add convenience method
(cherry picked from commit c02da99757)
2020-03-24 13:26:37 +01:00
Eelco Dolstra 1537e270fb Merge remote-tracking branch 'origin/master' into flakes 2020-03-20 13:15:11 +01:00
John Ericson 68fe0d9809 Add missing #include <regex> 2020-03-13 21:24:35 -04:00
Eelco Dolstra 35f6651735 Merge remote-tracking branch 'origin/master' into flakes 2020-03-11 17:03:38 +01:00
Eelco Dolstra e02481ded2 parseExprFromString(): Use std::string_view 2020-03-11 16:56:29 +01:00
Eelco Dolstra 73b6d87e17
Merge remote-tracking branch 'origin/master' into flakes 2020-03-04 13:58:42 +01:00
Eelco Dolstra 401b5bc541
builtins.cache: Cache regular expressions
The evaluator was spending about 1% of its time compiling a small
number of regexes over and over again.
2020-03-04 11:44:33 +01:00
Eelco Dolstra 9f4d8c6170 Pluggable fetchers
Flakes are now fetched using an extensible mechanism. Also lots of
other flake cleanups.
2020-01-21 22:56:04 +01:00
Eelco Dolstra ecb3a1afa2 Merge remote-tracking branch 'origin/master' into flakes 2019-12-11 14:53:30 +01:00
Eelco Dolstra bbe97dff8b Make the Store API more type-safe
Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.

Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.

Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).
2019-12-10 22:06:05 +01:00
Eelco Dolstra 0678e4d56a Move #include
(cherry picked from commit 8beedd4486)
2019-12-05 20:30:29 +01:00
Eelco Dolstra c3c23a52ee Merge remote-tracking branch 'origin/master' into flakes 2019-12-04 00:31:09 +01:00
Eelco Dolstra 2d6f1ddbb5
Remove builtins.valueSize
Fixes #3246.
2019-11-28 13:52:42 +01:00
Eelco Dolstra d12d69ea1a
Turn NIX_PATH into a config setting
This allows it to be set in nix.conf.
2019-11-22 23:07:35 +01:00
Eelco Dolstra fd8ee94ab2 Remove #include 2019-11-20 13:04:39 +01:00
Eelco Dolstra 8beedd4486 Move #include 2019-11-20 13:04:39 +01:00
Eelco Dolstra e491efe9fb
Use more stable registry URL 2019-11-06 14:20:16 +01:00
Eelco Dolstra b81d9d26f5
Merge remote-tracking branch 'origin/master' into flakes 2019-11-04 22:29:31 +01:00
Eelco Dolstra e012384fe9
Merge branch 'tojson-tostring-fix' of https://github.com/mayflower/nix 2019-10-27 12:18:35 +01:00
Robin Gloster e583df5280
builtins.toJSON: fix __toString usage 2019-10-27 10:15:51 +01:00
Eelco Dolstra 68e0f23edc Add flags to disallow dirty Git trees and to turn off warnings 2019-09-20 14:29:49 +02:00
Eelco Dolstra f97d3753a1
Require flake.nix to be an attrset (not a non-trivial thunk) 2019-09-09 17:34:38 +02:00
Eelco Dolstra c87840ae14
Don't allow arbitrary computations in flake attributes
E.g. you can write 'edition = 201909' but not 'edition = 201909 + 0'.

Fixes #3075.
2019-09-09 16:34:44 +02:00
Eelco Dolstra 89468410d5 Extract flake dependencies from the 'outputs' arguments
That is, instead of

  inputs = [ "nixpkgs" ];

  outputs = inputs: ... inputs.nixpkgs ...;

you can write

  outputs = { nixpkgs }: ... inputs.nixpkgs ...;
2019-08-30 11:22:34 +02:00
Eelco Dolstra ebc4dae517 Merge remote-tracking branch 'origin/master' into flakes 2019-08-29 16:11:38 +02:00
Graham Christensen ee9c988a1b
Track function start and ends for flame graphs
With this patch, and this file I called `log.py`:

    #!/usr/bin/env nix-shell
    #!nix-shell -i python3 -p python3 --pure

    import sys
    from pprint import pprint

    stack = []
    timestack = []

    for line in open(sys.argv[1]):
        components = line.strip().split(" ", 2)
        if components[0] != "function-trace":
            continue

        direction = components[1]
        components = components[2].rsplit(" ", 2)

        loc = components[0]
        _at = components[1]
        time = int(components[2])

        if direction == "entered":
            stack.append(loc)
            timestack.append(time)
        elif direction == "exited":
            dur = time - timestack.pop()
            vst = ";".join(stack)
            print(f"{vst} {dur}")
            stack.pop()

and:

    nix-instantiate --trace-function-calls -vvvv ../nixpkgs/pkgs/top-level/release.nix -A unstable > log.matthewbauer 2>&1
    ./log.py ./log.matthewbauer > log.matthewbauer.folded
    flamegraph.pl --title matthewbauer-post-pr log.matthewbauer.folded > log.matthewbauer.folded.svg

I can make flame graphs like: http://gsc.io/log.matthewbauer.folded.svg

---

Includes test cases around function call failures and tryEval. Uses
RAII so the finish is always called at the end of the function.
2019-08-14 16:09:35 -04:00
Eelco Dolstra 6e4a8c47f4
Put flake-related stuff in its own namespace 2019-05-29 15:31:07 +02:00
Eelco Dolstra 66f1d7ee95 Fetch the flake registry from the NixOS/flake-registry repo 2019-05-22 22:56:46 +02:00
Eelco Dolstra 3c171851a8 Make the URL/path of the global flake registry configurable 2019-05-07 22:49:13 +02:00
Nick Van den Broeck 24b35bf9e7 Fixed issue #13 2019-04-30 11:26:45 +02:00
Eelco Dolstra c101b29133 Merge remote-tracking branch 'tweag/flake-registries' into flakes 2019-03-27 14:40:36 +01:00
Eelco Dolstra b5565a7081 Merge remote-tracking branch 'origin/master' into flakes 2019-03-26 11:44:14 +01:00
Nick Van den Broeck a554f523db Combining registries properly 2019-03-23 13:42:48 +01:00
Eelco Dolstra ef52ccf035
experimental/optional -> optional 2019-03-14 14:10:52 +01:00
Eelco Dolstra beab05851b
nix: Add --flake flag
This allows using an arbitrary "provides" attribute from the specified
flake. For example:

  nix build --flake nixpkgs packages.hello

(Maybe provides.packages should be used for consistency...)
2019-02-12 21:55:43 +01:00
Eelco Dolstra ba05f29838
nix: Enable pure mode by default
We want to encourage a brave new world of hermetic evaluation for
source-level reproducibility, so flakes should not poke around in the
filesystem outside of their explicit dependencies.

Note that the default installation source remains impure in that it
can refer to mutable flakes, so "nix build nixpkgs.hello" still works
(and fetches the latest nixpkgs, unless it has been pinned by the
user).

A problem with pure evaluation is that builtins.currentSystem is
unavailable. For the moment, I've hard-coded "x86_64-linux" in the
nixpkgs flake. Eventually, "system" should be a flake function
argument.
2019-02-12 20:35:03 +01:00
Eelco Dolstra 91a6a47b0e
Improve flake references 2019-02-12 18:23:11 +01:00
Eelco Dolstra c8a0b9d5cb
experimental/optional -> optional 2019-02-12 13:43:32 +01:00
Eelco Dolstra 7a5cf31060
Initial flake support 2019-02-11 12:00:13 +01:00
Eelco Dolstra c02da99757
EvalState::allocAttr(): Add convenience method 2019-02-11 11:55:29 +01:00
Shea Levy 1d757292d0
Add builtins.getContext.
This can be very helpful when debugging, as well as enabling complex
black magic like surgically removing a single dependency from a
string's context.
2019-01-14 11:27:10 -05:00
Eelco Dolstra 875cd9da2b
Remove unused function printStats2()
Closes #2282.
2018-07-11 20:29:18 +02:00
Eelco Dolstra 30964103dc
Add temporary stats 2018-06-12 17:49:55 +02:00
Eelco Dolstra 24c6806994
Cache parse trees
This prevents EvalState::resetFileCache() from parsing everything all
over again.
2018-06-12 17:49:55 +02:00
Eelco Dolstra 1672bcd230
Move evaluator-specific settings out of libstore 2018-05-30 13:29:50 +02:00
Eelco Dolstra 4bb8741b98
Make Env self-describing
If the Env denotes a 'with', then values[0] may be an Expr* cast to a
Value*. For code that generically traverses Values/Envs, it's useful
to know this.
2018-05-22 16:02:32 +02:00
Eelco Dolstra 9fd7cf98db
Memoise checkSourcePath()
This prevents hydra-eval-jobs from statting the same files over and
over again.
2018-05-22 13:02:14 +02:00
Eelco Dolstra 53ec5ac69f
Fix some random -Wconversion warnings 2018-05-02 13:56:34 +02:00
Tuomas Tynkkynen 7e0360504d libexpr: Optimize prim_derivationStrict by using more symbol comparisons 2018-02-17 16:54:21 +02:00
Shea Levy 081f14a169
Allow using RegisterPrimop to define constants.
This enables plugins to add new constants, as well as new primops.
2018-02-08 14:35:50 -05:00
Eelco Dolstra d4dcffd643
Add pure evaluation mode
In this mode, the following restrictions apply:

* The builtins currentTime, currentSystem and storePath throw an
  error.

* $NIX_PATH and -I are ignored.

* fetchGit and fetchMercurial require a revision hash.

* fetchurl and fetchTarball require a sha256 attribute.

* No file system access is allowed outside of the paths returned by
  fetch{Git,Mercurial,url,Tarball}. Thus 'nix build -f ./foo.nix' is
  not allowed.

Thus, the evaluation result is completely reproducible from the
command line arguments. E.g.

  nix build --pure-eval '(
    let
      nix = fetchGit { url = https://github.com/NixOS/nixpkgs.git; rev = "9c927de4b179a6dd210dd88d34bda8af4b575680"; };
      nixpkgs = fetchGit { url = https://github.com/NixOS/nixpkgs.git; ref = "release-17.09"; rev = "66b4de79e3841530e6d9c6baf98702aa1f7124e4"; };
    in (import (nix + "/release.nix") { inherit nix nixpkgs; }).build.x86_64-linux
  )'

The goal is to enable completely reproducible and traceable
evaluation. For example, a NixOS configuration could be fully
described by a single Git commit hash. 'nixos-rebuild' would do
something like

  nix build --pure-eval '(
    (import (fetchGit { url = file:///my-nixos-config; rev = "..."; })).system
  ')

where the Git repository /my-nixos-config would use further fetchGit
calls or Git externals to fetch Nixpkgs and whatever other
dependencies it has. Either way, the commit hash would uniquely
identify the NixOS configuration and allow it to reproduced.
2018-01-16 19:23:18 +01:00
Eelco Dolstra 74f75c8558
import, builtins.readFile: Handle diverted stores
Fixes #1791
2018-01-12 17:31:08 +01:00
Eelco Dolstra 812e027e1d
Add option allowed-uris
This allows network access in restricted eval mode.
2017-10-30 12:41:49 +01:00
Eelco Dolstra 4c9ff89c26
nix-build/nix-shell: Eliminate call to nix-instantiate / nix-store
Note that this removes the need for a derivation symlink, so the
--drv-path and --add-drv-link flags now do nothing.
2017-07-26 17:29:09 +02:00
Eelco Dolstra fcca702a96
Replace a few bool flags with enums
Functions like copyClosure() had 3 bool arguments, which creates a
severe risk of mixing up arguments.

Also, implement copyClosure() using copyPaths().
2017-07-03 11:38:08 +02:00
Eelco Dolstra 6de33a9c67
Add support for passing structured data to builders
Previously, all derivation attributes had to be coerced into strings
so that they could be passed via the environment. This is lossy
(e.g. lists get flattened, necessitating configureFlags
vs. configureFlagsArray, of which the latter cannot be specified as an
attribute), doesn't support attribute sets at all, and has size
limitations (necessitating hacks like passAsFile).

This patch adds a new mode for passing attributes to builders, namely
encoded as a JSON file ".attrs.json" in the current directory of the
builder. This mode is activated via the special attribute

  __structuredAttrs = true;

(The idea is that one day we can set this in stdenv.mkDerivation.)

For example,

  stdenv.mkDerivation {
    __structuredAttrs = true;
    name = "foo";
    buildInputs = [ pkgs.hello pkgs.cowsay ];
    doCheck = true;
    hardening.format = false;
  }

results in a ".attrs.json" file containing (sans the indentation):

  {
    "buildInputs": [],
    "builder": "/nix/store/ygl61ycpr2vjqrx775l1r2mw1g2rb754-bash-4.3-p48/bin/bash",
    "configureFlags": [
      "--with-foo",
      "--with-bar=1 2"
    ],
    "doCheck": true,
    "hardening": {
      "format": false
    },
    "name": "foo",
    "nativeBuildInputs": [
      "/nix/store/10h6li26i7g6z3mdpvra09yyf10mmzdr-hello-2.10",
      "/nix/store/4jnvjin0r6wp6cv1hdm5jbkx3vinlcvk-cowsay-3.03"
    ],
    "propagatedBuildInputs": [],
    "propagatedNativeBuildInputs": [],
    "stdenv": "/nix/store/f3hw3p8armnzy6xhd4h8s7anfjrs15n2-stdenv",
    "system": "x86_64-linux"
  }

"passAsFile" is ignored in this mode because it's not needed - large
strings are included directly in the JSON representation.

It is up to the builder to do something with the JSON
representation. For example, in bash-based builders, lists/attrsets of
string values could be mapped to bash (associative) arrays.
2017-01-26 20:40:33 +01:00
Eelco Dolstra 215b70f51e
Revert "Get rid of unicode quotes (#1140)"
This reverts commit f78126bfd6. There
really is no need for such a massive change...
2016-11-26 00:38:01 +01:00
Guillaume Maudoux f78126bfd6 Get rid of unicode quotes (#1140) 2016-11-25 15:48:27 +01:00
Eelco Dolstra 92d917b71a Fix GC build 2016-08-30 13:12:12 +02:00
Eelco Dolstra c42d1acfeb forceBool(): Show position info 2016-08-29 19:37:19 +02:00
Eelco Dolstra 26d92017d3 Add builtin function "partition"
The implementation of "partition" in Nixpkgs is O(n^2) (because of the
use of ++), and for some reason was causing stack overflows in
multi-threaded evaluation (not sure why).

This reduces "nix-env -qa --drv-path" runtime by 0.197s and memory
usage by 298 MiB (in non-Boehm mode).
2016-08-29 19:36:54 +02:00
Eelco Dolstra d74236d1f2 nix build: Use Nix search path
That is, unless --file is specified, the Nix search path is
synthesized into an attribute set. Thus you can say

  $ nix build nixpkgs.hello

assuming $NIX_PATH contains an entry of the form "nixpkgs=...". This
is more verbose than

  $ nix build hello

but is less ambiguous.
2016-08-23 17:11:19 +02:00
Eelco Dolstra 363f37d084 Make the search path lazier with non-fatal errors
Thus, -I / $NIX_PATH entries are now downloaded only when they are
needed for evaluation. An error to download an entry is a non-fatal
warning (just like non-existant paths).

This does change the semantics of builtins.nixPath, which now returns
the original, rather than resulting path. E.g., before we had

  [ { path = "/nix/store/hgm3yxf1lrrwa3z14zpqaj5p9vs0qklk-nixexprs.tar.xz"; prefix = "nixpkgs"; } ... ]

but now

  [ { path = "https://nixos.org/channels/nixos-16.03/nixexprs.tar.xz"; prefix = "nixpkgs"; } ... ]

Fixes #792.
2016-04-14 15:32:24 +02:00
Eelco Dolstra 12b257f045 Make primop registration pluggable
This way we don't have to put all primops in one giant file.
2016-04-14 12:50:01 +02:00
Eelco Dolstra b3e8d72770 Merge pull request #762 from ctheune/ctheune-floats
Implement floats
2016-02-12 12:49:59 +01:00
Eelco Dolstra fa7cd5369b StoreAPI -> Store
Calling a class an API is a bit redundant...
2016-02-04 14:48:42 +01:00
Eelco Dolstra c10c61449f Eliminate the "store" global variable
Also, move a few free-standing functions into StoreAPI and Derivation.

Also, introduce a non-nullable smart pointer, ref<T>, which is just a
wrapper around std::shared_ptr ensuring that the pointer is never
null. (For reference-counted values, this is better than passing a
"T&", because the latter doesn't maintain the refcount. Usually, the
caller will have a shared_ptr keeping the value alive, but that's not
always the case, e.g., when passing a reference to a std::thread via
std::bind.)
2016-02-04 14:28:26 +01:00
Shea Levy 14080f3e4b Use __toString when coercing sets to strings.
For example, "${{ foo = "bar"; __toString = x: x.foo; }}" evaluates
to "bar".

With this, we can delay calling functions like mkDerivation,
buildPythonPackage, etc. until we actually need a derivation, enabling
overrides and other modifications to happen by simple attribute set
update.
2016-01-05 13:55:06 +01:00
Christian Theune 14ebde5289 First hit at providing support for floats in the language. 2016-01-05 00:40:40 +01:00
Mathnerd314 8a87521636 forceFunction: allow functors as well 2015-10-08 13:19:44 +02:00
Iwan Aucamp 75837651f1 Output line number on infinite recursion 2015-07-31 20:26:44 +02:00
Eelco Dolstra cb4320c1a0 Cleanup 2015-07-23 23:14:07 +02:00
Eelco Dolstra c8bb2371eb Optimize empty sets
This reduces the number of Bindings allocations by about 10%.
2015-07-23 23:11:08 +02:00
Nicolas B. Pierron db21cfa688 Move attribute set data structures into their own header file.
This modification moves Attr and Bindings structures into their own header
file which is dedicated to the attribute set representation. The goal of to
isolate pieces of code which are related to the attribute set
representation. Thus future modifications of the attribute set
representation will only have to modify these files, and not every other
file across the evaluator.
2015-07-14 19:23:17 +02:00
Eelco Dolstra 726f7f7fc9 Fix Boehm API violation
We were calling GC_INIT() after doing an allocation (in the baseEnv
construction), which is not allowed.
2015-03-19 20:02:37 +01:00
Eelco Dolstra 15d2d3c34e Add restricted evaluation mode
If ‘--option restrict-eval true’ is given, the evaluator will throw an
exception if an attempt is made to access any file outside of the Nix
search path. This is primarily intended for Hydra, where we don't want
people doing ‘builtins.readFile ~/.ssh/id_dsa’ or stuff like that.
2015-02-23 15:54:31 +01:00
Eelco Dolstra c2a8b5c42d Fix assertion failure in nix-env
$ nix-env -f ~/Dev/nixops/ -iA foo
  nix-env: src/libexpr/eval.hh:57: void nix::Bindings::push_back(const nix::Attr&): Assertion `size_ < capacity' failed.
  Aborted
2015-01-15 12:15:22 +01:00
Eelco Dolstra 153a943de7 Show position info for failing <...> lookups 2015-01-07 13:43:55 +01:00
Eelco Dolstra 8aedaf111e Remove canary stuff 2014-12-12 10:59:50 +01:00
Eelco Dolstra 4e340a983f forceString(): Accept pos argument 2014-11-25 10:23:36 +01:00
Shea Levy 997defa166 Add functors (callable attribute sets).
With this, attribute sets with a `__functor` attribute can be applied
just like normal functions. This can be used to attach arbitrary
metadata to a function without callers needing to treat it specially.
2014-11-15 16:12:05 -05:00
Shea Levy 6062b12160 Fix build on gcc < 4.7 2014-10-20 12:15:50 -04:00
Shea Levy d16e3c7f09 Export realiseContext in libnixexpr
Useful for importNative plugins
2014-10-17 22:15:09 -04:00
Eelco Dolstra 0ed1b924be Bindings: Remove copy constructor 2014-09-24 15:29:05 +02:00
Eelco Dolstra 1e0a799bef Rename strictForceValue -> forceValueDeep 2014-09-22 16:05:00 +02:00
Eelco Dolstra eff120d1b9 Add a function ‘valueSize’
It returns the size of value, including all other values and
environments reachable from it. It is intended for debugging memory
consumption issues.
2014-09-22 16:05:00 +02:00
Eelco Dolstra 93e4f01ee3 Inline Bindings::find() 2014-09-19 16:56:13 +02:00
Eelco Dolstra 5b58991a71 Store Attrs inside Bindings
This prevents a double allocation per attribute set.
2014-09-19 16:49:41 +02:00
Eelco Dolstra 6e5b02bee4 Add some instrumentation for debugging GC leaks 2014-09-17 15:19:07 +02:00
Eelco Dolstra fefd3650d4 Fix a segfault in ‘nix-env -qa’
This was triggered by 47e185847e, which
turned globals.state into a pointer.
2014-08-21 00:05:17 +02:00
Eelco Dolstra 62a6eeb1f3 Make the Nix search path declarative
Nix search path lookups like <nixpkgs> are now desugared to ‘findFile
nixPath <nixpkgs>’, where ‘findFile’ is a new primop. Thus you can
override the search path simply by saying

  let
    nixPath = [ { prefix = "nixpkgs"; path = "/my-nixpkgs"; } ];
  in ... <nixpkgs> ...

In conjunction with ‘scopedImport’ (commit
c273c15cb1), the Nix search path can be
propagated across imports, e.g.

  let

    overrides = {
      nixPath = [ ... ] ++ builtins.nixPath;
      import = fn: scopedImport overrides fn;
      scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
      builtins = builtins // overrides;
    };

  in scopedImport overrides ./nixos
2014-05-26 17:02:22 +02:00
Eelco Dolstra 39d72640c2 Ensure that -I flags get included in nixPath
Also fixes #261.
2014-05-26 16:52:31 +02:00
Eelco Dolstra c273c15cb1 Add primop ‘scopedImport’
‘scopedImport’ works like ‘import’, except that it takes a set of
attributes to be added to the lexical scope of the expression,
essentially extending or overriding the builtin variables.  For
instance, the expression

  scopedImport { x = 1; } ./foo.nix

where foo.nix contains ‘x’, will evaluate to 1.

This has a few applications:

* It allows getting rid of function argument specifications in package
  expressions. For instance, a package expression like:

    { stdenv, fetchurl, libfoo }:

    stdenv.mkDerivation { ... buildInputs = [ libfoo ]; }

  can now we written as just

    stdenv.mkDerivation { ... buildInputs = [ libfoo ]; }

  and imported in all-packages.nix as:

    bar = scopedImport pkgs ./bar.nix;

  So whereas we once had dependencies listed in three places
  (buildInputs, the function, and the call site), they now only need
  to appear in one place.

* It allows overriding builtin functions. For instance, to trace all
  calls to ‘map’:

  let
    overrides = {
      map = f: xs: builtins.trace "map called!" (map f xs);

      # Ensure that our override gets propagated by calls to
      # import/scopedImport.
      import = fn: scopedImport overrides fn;

      scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;

      # Also update ‘builtins’.
      builtins = builtins // overrides;
    };
  in scopedImport overrides ./bla.nix

* Similarly, it allows extending the set of builtin functions. For
  instance, during Nixpkgs/NixOS evaluation, the Nixpkgs library
  functions could be added to the default scope.

There is a downside: calls to scopedImport are not memoized, unlike
import. So importing a file multiple times leads to multiple parsings
/ evaluations. It would be possible to construct the AST only once,
but that would require careful handling of variables/environments.
2014-05-26 14:26:29 +02:00