Raito Bezariusandeldritch horrors
37ccd28c3b
`builtins.storePath` allows you to use "external" knowledge of present
store paths in your store to be used in your expressions.
This is sometimes used to avoid double wrapping store paths, for example
when dealing with nixpkgs sources (`builtins.storePath pkgs.path` is a
frequent pattern).
Unfortunately, using your external knowledge of present store paths is
technically impure because Flakes is about not depending on the *STATE*
of your store, no matter what you know about it or what you do to ensure
that your knowledge is accurate.
That being said, `builtins.storePath` is already possible in the
fragment of "pure Nixlang" via a clever use of `builtins.appendContext`.
Precisely:
```
storePath = path:
let path' = builtins.unsafeDiscardStringContext path;
in
# NOTE: merging the context set in all generality is impossible
because getContext on a pure path doesn't work.
builtins.appendContext path' { ${path'} = { path = true; }; };
```
works in pure contexts.
Because of this, we deem that storePath should be allowed in pure
contexts and users do not have to come up with a `storePath` polyfill.
Fixes #402.
Change-Id: I5fff750a4feed082745431835db451f945249cfb
Signed-off-by: Raito Bezarius <raito@lix.systems>
96 lines
3.1 KiB
Python
96 lines
3.1 KiB
Python
from testlib.fixtures.nix import Nix
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from testlib.utils import get_global_asset
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from testlib.fixtures.file_helper import File, with_files
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from testlib.fixtures.env import ManagedEnv
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from pathlib import Path
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import pytest
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files = {
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"config.nix": get_global_asset("config.nix"),
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"default.nix": File("""
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with import ./config.nix;
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rec {
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existing = mkDerivation {
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name = "existing";
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buildCommand = ''
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echo meow > $out
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'';
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};
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reuse-existing = mkDerivation {
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name = "reuse-existing";
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buildCommand = ''
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cat ${builtins.storePath existing.outPath} > $out
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'';
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};
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}
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"""),
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"flake.nix": File("""
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{ outputs = _: (import ./default.nix); }
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"""),
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}
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@with_files(files)
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def test_primop_store_path_exists(nix: Nix):
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# We build the `existing` path, it's in the store now.
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nix.nix_build(["-A", "existing"]).run().ok()
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nix.nix_build(["-A", "reuse-existing"]).run().ok()
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@with_files(files)
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@pytest.mark.parametrize("under_pure_eval", [True, False])
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def test_primop_store_path_missing(nix: Nix, under_pure_eval: bool):
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extra_options = ["--pure-eval"] if under_pure_eval else []
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# We did not build `existing` path, this should fail.
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nix.nix_build(["-A", "reuse-existing", *extra_options]).run().expect(1)
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@with_files(files)
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class TestPrimopStorePathSubstitutes:
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@pytest.fixture(autouse=True)
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def setup(self, nix: Nix, env: ManagedEnv, files: Path):
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# We build `existing` path.
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self.output = (
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nix.nix_build([str(files / "default.nix"), "-A", "existing"]).run().ok().stdout_plain
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)
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cache_dir = env.dirs.home / "cache"
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nix.nix(
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["copy", self.output, "--to", f"file://{cache_dir}", "--no-require-sigs"], flake=True
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).run().ok()
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nix.clear_store()
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nix.settings.substituters = f"file://{cache_dir}"
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nix.settings.require_sigs = False
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def test_restricted_eval(self, nix: Nix, env: ManagedEnv):
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# Using -I lists it as an allowed path.
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nix.nix_build(
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[
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"-A",
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"reuse-existing",
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"--restrict-eval",
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"-I",
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f"test_file={env.dirs.home}/default.nix",
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"-I",
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f"test_file={env.dirs.home}/config.nix",
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]
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).run().ok()
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def test_pure_eval(self, nix: Nix):
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# nix2 cli can't load expressions from file systems in pure eval mode.
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# nix3 cli substitute in sandboxes because they have no network, where
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# it will just hard-disable all substitution. even for file:// caches.
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expr = f"""
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derivation {{
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name = "reuse-existing";
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system = "f2";
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builder = "/bin/sh";
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args = [ "-c" "echo ${{builtins.storePath "{self.output}"}} >$out" ];
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}}
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"""
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nix.nix_build(["--pure-eval", "--system", "f2", "--expr", expr]).run().ok()
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def test_impure(self, nix: Nix):
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nix.nix_build(["-A", "reuse-existing"]).run().ok()
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