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feat(tvix/eval): don't warn twice about dead code

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We currently send two warnings in case of detecting dead code - W008
inside compile_dead_code, and a more detailed warning in all places that
invoke compile_dead_code:

```
warning[W007]: useless operation on boolean: this expression is always false
     --> /nix/store/qz3gjn95gazab4fkb7s8lm6hz17rdzzy-414z9nnj1wy66ymq6vgb693x9xjz6hf2-nixpkgs-src/pkgs/top-level/perl-packages.nix:12079:15
      |
12079 |     doCheck = false && !stdenv.isDarwin;
      |               ^^^^^^^^^^^^^^^^^^^^^^^^^

warning[W008]: this code will never be executed
     --> /nix/store/qz3gjn95gazab4fkb7s8lm6hz17rdzzy-414z9nnj1wy66ymq6vgb693x9xjz6hf2-nixpkgs-src/pkgs/top-level/perl-packages.nix:12079:24
      |
12079 |     doCheck = false && !stdenv.isDarwin;
      |                        ^^^^^^^^^^^^^^^^
```

The place invoking `compile_dead_code` has more context to why the code
is unused, so it's error message is much more useful.

Stop emitting the less informative warning inside compile_dead_code
(W008), and update the comment that we expect the caller to emit a
warning.

I kept W008 itself still around, in case we end up having places this
will get used again.

Change-Id: I2c5d84fc0cb4035872cd4b71cc3e9e34e120eb37
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8024
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: raitobezarius <tvl@lahfa.xyz>
This commit is contained in:
Florian Klink 2023-02-03 12:38:41 +01:00 • committed by clbot
parent e4687765d7
commit c9c8b10370
1 changed files with 3 additions and 1 deletions
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4
tvix/eval/src/compiler/mod.rs
View file

@ -302,9 +302,11 @@ impl Compiler<'_> {
/// Compiles an expression, but does not emit any code for it as
/// it is considered dead. This will still catch errors and
/// warnings in that expression.
///
/// A warning about the that code being dead is assumed to already be
/// emitted by the caller of [compile_dead_code].
fn compile_dead_code(&mut self, slot: LocalIdx, node: ast::Expr) {
self.dead_scope += 1;
self.emit_warning(&node, WarningKind::DeadCode);
self.compile(slot, node);
self.dead_scope -= 1;
}