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Substitute erased lifetimes on bad placeholder type
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Fix rust-lang#82455.

(cherry picked from commit 5ad6088)
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estebank authored and cuviper committed Mar 10, 2021
1 parent 3ad36d2 commit 3fee12f
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Showing 3 changed files with 44 additions and 2 deletions.
12 changes: 12 additions & 0 deletions compiler/rustc_typeck/src/collect.rs
Original file line number Diff line number Diff line change
Expand Up @@ -331,6 +331,11 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
span: Span,
) -> &'tcx Const<'tcx> {
bad_placeholder_type(self.tcx(), vec![span]).emit();
// Typeck doesn't expect erased regions to be returned from `type_of`.
let ty = self.tcx.fold_regions(ty, &mut false, |r, _| match r {
ty::ReErased => self.tcx.lifetimes.re_static,
_ => r,
});
self.tcx().const_error(ty)
}

Expand Down Expand Up @@ -1536,6 +1541,12 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
match get_infer_ret_ty(&sig.decl.output) {
Some(ty) => {
let fn_sig = tcx.typeck(def_id).liberated_fn_sigs()[hir_id];
// Typeck doesn't expect erased regions to be returned from `type_of`.
let fn_sig = tcx.fold_regions(fn_sig, &mut false, |r, _| match r {
ty::ReErased => tcx.lifetimes.re_static,
_ => r,
});

let mut visitor = PlaceholderHirTyCollector::default();
visitor.visit_ty(ty);
let mut diag = bad_placeholder_type(tcx, visitor.0);
Expand Down Expand Up @@ -1564,6 +1575,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
}
}
diag.emit();

ty::Binder::bind(fn_sig)
}
None => AstConv::ty_of_fn(
Expand Down
12 changes: 12 additions & 0 deletions src/test/ui/typeck/typeck_type_placeholder_item.rs
Original file line number Diff line number Diff line change
Expand Up @@ -208,3 +208,15 @@ impl Qux for Struct {
const D: _ = 42;
//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
}

fn map<T>(_: fn() -> Option<&'static T>) -> Option<T> {
None
}

fn value() -> Option<&'static _> {
//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
Option::<&'static u8>::None
}

const _: Option<_> = map(value);
//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
22 changes: 20 additions & 2 deletions src/test/ui/typeck/typeck_type_placeholder_item.stderr
Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,7 @@ LL | fn test11(x: &usize) -> &_ {
| -^
| ||
| |not allowed in type signatures
| help: replace with the correct return type: `&&usize`
| help: replace with the correct return type: `&'static &'static usize`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> $DIR/typeck_type_placeholder_item.rs:52:52
Expand Down Expand Up @@ -410,6 +410,24 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
LL | type Y = impl Trait<_>;
| ^ not allowed in type signatures

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> $DIR/typeck_type_placeholder_item.rs:216:31
|
LL | fn value() -> Option<&'static _> {
| ----------------^-
| | |
| | not allowed in type signatures
| help: replace with the correct return type: `Option<&'static u8>`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> $DIR/typeck_type_placeholder_item.rs:221:10
|
LL | const _: Option<_> = map(value);
| ^^^^^^^^^
| |
| not allowed in type signatures
| help: replace `_` with the correct type: `Option<u8>`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
--> $DIR/typeck_type_placeholder_item.rs:140:31
|
Expand Down Expand Up @@ -614,7 +632,7 @@ LL | const D: _ = 42;
| not allowed in type signatures
| help: replace `_` with the correct type: `i32`

error: aborting due to 67 previous errors
error: aborting due to 69 previous errors

Some errors have detailed explanations: E0121, E0282, E0403.
For more information about an error, try `rustc --explain E0121`.

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