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Rollup merge of #133368 - compiler-errors:codegen-select-unconstrained-params, r=lcnr

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Delay a bug when encountering an impl with unconstrained generics in `codegen_select`

Despite its name, `codegen_select` is what powers `Instance::try_resolve`, which is used in pre-codegen contexts to try to resolve a method where possible. One place that it's used is in the "recursion MIR lint" that detects recursive MIR bodies.

If we encounter an impl in `codegen_select` that contains unconstrained generic parameters, we expect that impl to caused an error to be reported; however, there's no temporal guarantee that this error is reported *before* we call `codegen_select`. This is what a delayed bug is *for*, and this PR makes us use a delayed bug rather than asserting something about errors already having been emitted.

Fixes  #126646
This commit is contained in:
Guillaume Gomez
2024-11-28 03:14:46 +01:00
committed by GitHub
parent 09734ac3af 50fb40a987
commit acf48fcb9d
4 changed files with 44 additions and 24 deletions
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21
compiler/rustc_traits/src/codegen.rs
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@@ -74,12 +74,21 @@ pub(crate) fn codegen_select_candidate<'tcx>(
}
let impl_source = infcx.resolve_vars_if_possible(impl_source);
let impl_source = infcx.tcx.erase_regions(impl_source);
if impl_source.has_infer() {
// Unused lifetimes on an impl get replaced with inference vars, but never resolved,
// causing the return value of a query to contain inference vars. We do not have a concept
// for this and will in fact ICE in stable hashing of the return value. So bail out instead.
infcx.tcx.dcx().has_errors().unwrap();
let impl_source = tcx.erase_regions(impl_source);
if impl_source.has_non_region_infer() {
// Unused generic types or consts on an impl get replaced with inference vars,
// but never resolved, causing the return value of a query to contain inference
// vars. We do not have a concept for this and will in fact ICE in stable hashing
// of the return value. So bail out instead.
match impl_source {
ImplSource::UserDefined(impl_) => {
tcx.dcx().span_delayed_bug(
tcx.def_span(impl_.impl_def_id),
"this impl has unconstrained generic parameters",
);
}
_ => unreachable!(),
}
return Err(CodegenObligationError::FulfillmentError);
}