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Rollup merge of #132971 - BoxyUwU:handle_infers_in_anon_consts, r=compiler-errors

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Handle infer vars in anon consts on stable

Fixes #132955

Diagnostics will sometimes try to replace generic parameters with inference variables in failing goals. This means that if we have some failing goal with an array repeat expr count anon const in it, we will wind up with some `ty::ConstKind::Unevaluated(anon_const_def, [?x])` during diagnostics which will then ICE if we do not handle inference variables correctly on stable when normalizing type system consts.

r? ```@compiler-errors```
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Jubilee 2024-11-13 22:43:37 -08:00 • committed by GitHub
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30
compiler/rustc_trait_selection/src/traits/mod.rs
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@ -578,16 +578,28 @@ pub fn try_evaluate_const<'tcx>(
(args, param_env)
}
}
} else {
// FIXME: We don't check anything on stable as the only way we can wind up with
// an unevaluated constant containing generic parameters is through array repeat
// expression counts which have a future compat lint for usage of generic parameters
// instead of a hard error.
} else if tcx.def_kind(uv.def) == DefKind::AnonConst && uv.has_non_region_infer() {
// FIXME: remove this when `const_evaluatable_unchecked` is a hard error.
//
// This codepath is however also reachable by `generic_const_exprs` and some other
// feature gates which allow constants in the type system to use generic parameters.
// In theory we should be checking for generic parameters here and returning an error
// in such cases.
// Diagnostics will sometimes replace the identity args of anon consts in
// array repeat expr counts with inference variables so we have to handle this
// even though it is not something we should ever actually encounter.
//
// Array repeat expr counts are allowed to syntactically use generic parameters
// but must not actually depend on them in order to evalaute succesfully. This means
// that it is actually fine to evalaute them in their own environment rather than with
// the actually provided generic arguments.
tcx.dcx().delayed_bug(
"Encountered anon const with inference variable args but no error reported",
);
let args = GenericArgs::identity_for_item(tcx, uv.def);
let param_env = tcx.param_env(uv.def);
(args, param_env)
} else {
// FIXME: This codepath is reachable under `associated_const_equality` and in the
// future will be reachable by `min_generic_const_args`. We should handle inference
// variables and generic parameters properly instead of doing nothing.
(uv.args, param_env)
};
let uv = ty::UnevaluatedConst::new(uv.def, args);