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Don't suggest types whose inner type is erroneous #91450

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Dec 5, 2021
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Don't suggest types whose inner type is erroneous #91450

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4 changes: 2 additions & 2 deletions compiler/rustc_typeck/src/collect.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@ use rustc_middle::ty::subst::InternalSubsts;
use rustc_middle::ty::util::Discr;
use rustc_middle::ty::util::IntTypeExt;
use rustc_middle::ty::{self, AdtKind, Const, DefIdTree, Ty, TyCtxt};
use rustc_middle::ty::{ReprOptions, ToPredicate, WithConstness};
use rustc_middle::ty::{ReprOptions, ToPredicate, TypeFoldable, WithConstness};
use rustc_session::lint;
use rustc_session::parse::feature_err;
use rustc_span::symbol::{kw, sym, Ident, Symbol};
Expand Down Expand Up @@ -1779,7 +1779,7 @@ fn fn_sig(tcx: TyCtxt<'_>, def_id: DefId) -> ty::PolyFnSig<'_> {
visitor.visit_ty(ty);
let mut diag = bad_placeholder_type(tcx, visitor.0, "return type");
let ret_ty = fn_sig.skip_binder().output();
if ret_ty != tcx.ty_error() {
if !ret_ty.references_error() {
if !ret_ty.is_closure() {
let ret_ty_str = match ret_ty.kind() {
// Suggest a function pointer return type instead of a unique function definition
Expand Down
7 changes: 7 additions & 0 deletions src/test/ui/typeck/issue-91450-inner-ty-error.rs
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@@ -0,0 +1,7 @@
// Regression test for #91450.
// This test ensures that the compiler does not suggest `Foo<[type error]>` in diagnostic messages.

fn foo() -> Option<_> {} //~ ERROR: [E0308]
//~^ ERROR: the type placeholder `_` is not allowed
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I wanted to add a "negative" test of "help: replace with the correct return type: Foo<[type error]>" here to detect any regressions in the future but IIRC there isn't such annotation ;)


fn main() {}
21 changes: 21 additions & 0 deletions src/test/ui/typeck/issue-91450-inner-ty-error.stderr
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@@ -0,0 +1,21 @@
error[E0308]: mismatched types
--> $DIR/issue-91450-inner-ty-error.rs:4:13
|
LL | fn foo() -> Option<_> {}
| --- ^^^^^^^^^ expected enum `Option`, found `()`
| |
| implicitly returns `()` as its body has no tail or `return` expression
|
= note: expected enum `Option<_>`
found unit type `()`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures for return types
--> $DIR/issue-91450-inner-ty-error.rs:4:20
|
LL | fn foo() -> Option<_> {}
| ^ not allowed in type signatures

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0121, E0308.
For more information about an error, try `rustc --explain E0121`.