As described in #4745 it's otherwise fairly hard to understand where
this is coming from. Say you have an expression which uses e.g.
`types.package`:
``` nix
{ outputs = { self, nixpkgs }: {
packages.x86_64-linux.hello = let
foo = nixpkgs.lib.evalModules {
modules = [
{
options.foo.bar = with nixpkgs.lib; mkOption { type = types.package; };
}
{
foo.bar = ./.;
}
];
};
in builtins.trace foo.config.foo.bar.outPath nixpkgs.legacyPackages.x86_64-linux.hello;
defaultPackage.x86_64-linux = self.packages.x86_64-linux.hello;
};
}
```
Then you'll get an error trace like this:
```
error: 'builtins.storePath' is not allowed in pure evaluation mode
at /nix/store/p4h2x6r80njkb0j2rc1xjhhl99yri3zb-source/lib/attrsets.nix:328:15:
327| let
328| path' = builtins.storePath path;
| ^
329| res =
… while evaluating the attribute 'config.foo.bar.outPath'
at /nix/store/p4h2x6r80njkb0j2rc1xjhhl99yri3zb-source/lib/attrsets.nix:332:11:
331| name = sanitizeDerivationName (builtins.substring 33 (-1) (baseNameOf path'));
332| outPath = path';
| ^
333| outputs = [ "out" ];
… while evaluating the attribute 'packages.x86_64-linux.hello'
at /nix/store/6c1rfsqzrhjw1235palzjmf5vihcpci7-source/flake.nix:3:5:
2| { outputs = { self, nixpkgs }: {
3| packages.x86_64-linux.hello = let
| ^
4| foo = nixpkgs.lib.evalModules {
```
Fixes#4745
They are equivalent according to
<https://spec.commonmark.org/0.29/#hard-line-breaks>,
and the trailing spaces tend to be a pain (because the make git
complain, editors tend to want to remove them − the `.editorconfig`
actually specifies that − etc..).
This function doesn't support all compression methods (i.e. 'none' and
'br') so it shouldn't be exposed.
Also restore the original decompress() as a wrapper around
makeDecompressionSink().
The S3 store relies on the ability to be able to decompress things with
an empty method, because it just passes the value of the Content-Encoding
directly to decompress.
If the file is not compressed, then this will cause the compression
routine to get confused.
This caused NixOS/nixpkgs#120120.
This makes Nix look up paths derivations when they are passed as a
store paths. So:
$ nix path-info --derivation /nix/store/0pisd259nldh8yfjvw663mspm60cn5v8-hello-2.10
now gives
/nix/store/qp724w90516n4bk5r9gfb37vzmqdh3z7-hello-2.10.drv
instead of "".
If no deriver is available, Nix now errors instead of silently
ignoring that argument.
In case of pure input-addressed derivations, the build loop doesn't
guaranty that the realisations are stored in the db (if the output paths
are already there or can be substituted, the realisations won't be
registered). This caused `nix shell` to fail in some cases because it
was assuming that the realisations were always existing.
A better (but more involved) fix would probably to ensure that we always
register the realisations, but in the meantime this patches the surface
issue.
Fix#4721
I think that it's not very helpful to get "cached failures" in a wrong
`flake.nix`. This can be very confusing when debugging a Nix expression.
See for instance NixOS/nixpkgs#118115.
In fact, the eval cache allows a forced reevaluation which is used for
e.g. `nix eval`.
This change makes sure that this is the case for `nix build` as well. So
rather than
λ ma27 [~/Projects/exp] → ../nix/outputs/out/bin/nix build -L --rebuild --experimental-features 'nix-command flakes'
error: cached failure of attribute 'defaultPackage.x86_64-linux'
the evaluation of already-evaluated (and failed) attributes looks like
this now:
λ ma27 [~/Projects/exp] → ../nix/outputs/out/bin/nix build -L --rebuild --experimental-features 'nix-command flakes'
error: attribute 'hell' missing
at /nix/store/mrnvi9ss8zn5wj6gpn4bcd68vbh42mfh-source/flake.nix:6:35:
5|
6| packages.x86_64-linux.hello = nixpkgs.legacyPackages.x86_64-linux.hell;
| ^
7|
(use '--show-trace' to show detailed location information)
When working on some more complex Nix code, there are sometimes rather
unhelpful or misleading error messages, especially if coerce-errors are
thrown.
This patch is a first steps towards improving that. I'm happy to file
more changes after that, but I'd like to gather some feedback first.
To summarize, this patch does the following things:
* Attrsets (a.k.a. `Bindings` in `libexpr`) now have a `Pos`. This is
helpful e.g. to identify which attribute-set in `listToAttrs` is
invalid.
* The `Value`-struct has a new method named `determinePos` which tries
to guess the position of a value and falls back to a default if that's
not possible.
This can be used to provide better messages if a coercion fails.
* The new `determinePos`-API is used by `builtins.concatMap` now. With
that change, Nix shows the exact position in the error where a wrong
value was returned by the lambda.
To make sure it's still obvious that `concatMap` is the problem,
another stack-frame was added.
* The changes described above can be added to every other `primop`, but
first I'd like to get some feedback about the overall approach.
* The position of the `name`-attribute appears in the trace.
* If e.g. `meta` has no `outPath`-attribute, a `cannot coerce set to
string` error will be thrown where `pos` points to `name =` which is
highly misleading.
