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Rollup merge of #118000 - compiler-errors:placeholder-ty-outlives, r=aliemjay

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Make regionck care about placeholders in outlives components

Currently, we don't consider a placeholder type `!T` to be a type component when it comes to processing type-outlives obligations. This means that they are essentially treated like unit values with no sub-components, and always outlive any region. This is problematic for `non_lifetime_binders`, and even more problematic for `with_negative_coherence`, since negative coherence uses placeholders as universals.

This PR adds `Component::Placeholder` which acts much like `Component::Param`. This currently causes a regression in some non-lifetime-binders tests because `for<T> T: 'static` doesn't imply itself when processing outlives obligations, so code like this will fail:

```
fn foo() where for<T> T: 'static {
  foo() //~ fails
}
```

Since the where clause doesn't imply itself. This requires making the `MatchAgainstHigherRankedOutlives` relation smarter when it comes to binders.

r? types
This commit is contained in:
Michael Goulet 2023-11-19 19:14:35 -08:00 • committed by GitHub
commit 6388c0ef04
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16 changed files with 177 additions and 13 deletions
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10
compiler/rustc_trait_selection/src/traits/coherence.rs
View file

@ -398,7 +398,8 @@ fn impl_intersection_has_negative_obligation(
debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id);
let ref infcx = tcx.infer_ctxt().intercrate(true).with_next_trait_solver(true).build();
let universe = infcx.universe();
let root_universe = infcx.universe();
assert_eq!(root_universe, ty::UniverseIndex::ROOT);
let impl1_header = fresh_impl_header(infcx, impl1_def_id);
let param_env =
@ -414,7 +415,12 @@ fn impl_intersection_has_negative_obligation(
return false;
};
plug_infer_with_placeholders(infcx, universe, (impl1_header.impl_args, impl2_header.impl_args));
plug_infer_with_placeholders(
infcx,
root_universe,
(impl1_header.impl_args, impl2_header.impl_args),
);
let param_env = infcx.resolve_vars_if_possible(param_env);
// FIXME(with_negative_coherence): the infcx has constraints from equating
// the impl headers. We should use these constraints as assumptions, not as

3
compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
View file

@ -208,6 +208,9 @@ fn implied_bounds_from_components<'tcx>(
Component::Region(r) => Some(OutlivesBound::RegionSubRegion(sub_region, r)),
Component::Param(p) => Some(OutlivesBound::RegionSubParam(sub_region, p)),
Component::Alias(p) => Some(OutlivesBound::RegionSubAlias(sub_region, p)),
Component::Placeholder(_) => {
unimplemented!("Shouldn't expect a placeholder type in implied bounds (yet)")
}
Component::EscapingAlias(_) =>
// If the projection has escaping regions, don't
// try to infer any implied bounds even for its