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Ensure that early-bound function lifetimes are always 'local'

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During borrowchecking, we treat any free (early-bound) regions on
the 'defining type' as `RegionClassification::External`. According
to the doc comments, we should only have 'external' regions when
checking a closure/generator.

However, a plain function can also have some if its regions
be considered 'early bound' - this occurs when the region is
constrained by an argument, appears in a `where` clause, or
in an opaque type. This was causing us to incorrectly mark these
regions as 'external', which caused some diagnostic code
to act as if we were referring to a 'parent' region from inside
a closure.

This PR marks all instantiated region variables as 'local'
when we're borrow-checking something other than a
closure/generator/inline-const.
This commit is contained in:
Aaron Hill 2021-12-31 16:55:34 -05:00
parent 984a6bf9c1
commit e3a048c3c9
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GPG key ID: B4087E510E98B164
38 changed files with 98 additions and 124 deletions
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41
compiler/rustc_borrowck/src/universal_regions.rs
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@ -180,8 +180,9 @@ pub enum RegionClassification {
/// anywhere. There is only one, `'static`.
Global,
/// An **external** region is only relevant for closures. In that
/// case, it refers to regions that are free in the closure type
/// An **external** region is only relevant for
/// closures, generators, and inline consts. In that
/// case, it refers to regions that are free in the type
/// -- basically, something bound in the surrounding context.
///
/// Consider this example:
@ -198,8 +199,8 @@ pub enum RegionClassification {
/// Here, the lifetimes `'a` and `'b` would be **external** to the
/// closure.
///
/// If we are not analyzing a closure, there are no external
/// lifetimes.
/// If we are not analyzing a closure/generator/inline-const,
/// there are no external lifetimes.
External,
/// A **local** lifetime is one about which we know the full set
@ -424,22 +425,30 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
let typeck_root_def_id = self.infcx.tcx.typeck_root_def_id(self.mir_def.did.to_def_id());
// If this is a closure or generator, then the late-bound regions from the enclosing
// function are actually external regions to us. For example, here, 'a is not local
// to the closure c (although it is local to the fn foo):
// fn foo<'a>() {
// let c = || { let x: &'a u32 = ...; }
// }
if self.mir_def.did.to_def_id() != typeck_root_def_id {
// If this is is a 'root' body (not a closure/generator/inline const), then
// there are no extern regions, so the local regions start at the same
// position as the (empty) sub-list of extern regions
let first_local_index = if self.mir_def.did.to_def_id() == typeck_root_def_id {
first_extern_index
} else {
// If this is a closure, generator, or inline-const, then the late-bound regions from the enclosing
// function are actually external regions to us. For example, here, 'a is not local
// to the closure c (although it is local to the fn foo):
// fn foo<'a>() {
// let c = || { let x: &'a u32 = ...; }
// }
self.infcx
.replace_late_bound_regions_with_nll_infer_vars(self.mir_def.did, &mut indices)
}
let bound_inputs_and_output = self.compute_inputs_and_output(&indices, defining_ty);
.replace_late_bound_regions_with_nll_infer_vars(self.mir_def.did, &mut indices);
// Any regions created during the execution of `defining_ty` or during the above
// late-bound region replacement are all considered 'extern' regions
self.infcx.num_region_vars()
};
// "Liberate" the late-bound regions. These correspond to
// "local" free regions.
let first_local_index = self.infcx.num_region_vars();
let bound_inputs_and_output = self.compute_inputs_and_output(&indices, defining_ty);
let inputs_and_output = self.infcx.replace_bound_regions_with_nll_infer_vars(
FR,
self.mir_def.did,