Auto merge of #69148 - estebank:cold-as-ice, r=oli-obk

Account for bounds and asociated items when denying `_`

Fix #68801, #69204. Follow up to #67597 and #68071.

Output for the original ICE report:

```
    Checking vinoteca v5.0.0 (/Users/ekuber/workspace/vinoteca)
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
  --> src/producers.rs:43:70
   |
43 | pub fn top<Table: diesel::Table + diesel::query_dsl::InternalJoinDsl<_, diesel::query_source::joins::Inner, _>>(table: Table, limit: usize, connection: DbConn) -> RestResult<Vec<TopWineType>> {
   |                                                                      ^ not allowed in type signatures       ^ not allowed in type signatures

error: aborting due to previous error
```

src/librustc_typeck/astconv.rs

@@ -514,7 +514,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         self_ty: Option<Ty<'tcx>>,
         arg_count_correct: bool,
         args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
-        provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
+        mut provided_kind: impl FnMut(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
         mut inferred_kind: impl FnMut(
             Option<&[subst::GenericArg<'tcx>]>,
             &GenericParamDef,
@@ -751,6 +751,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         };
 
         let mut missing_type_params = vec![];
+        let mut inferred_params = vec![];
         let substs = Self::create_substs_for_generic_args(
             tcx,
             def_id,
@@ -773,7 +774,12 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     self.ast_region_to_region(&lt, Some(param)).into()
                 }
                 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
-                    self.ast_ty_to_ty(&ty).into()
+                    if let (hir::TyKind::Infer, false) = (&ty.kind, self.allow_ty_infer()) {
+                        inferred_params.push(ty.span);
+                        tcx.types.err.into()
+                    } else {
+                        self.ast_ty_to_ty(&ty).into()
+                    }
                 }
                 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
                     self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
@@ -832,6 +838,18 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                 }
             },
         );
+        if !inferred_params.is_empty() {
+            // We always collect the spans for placeholder types when evaluating `fn`s, but we
+            // only want to emit an error complaining about them if infer types (`_`) are not
+            // allowed. `allow_ty_infer` gates this behavior.
+            crate::collect::placeholder_type_error(
+                tcx,
+                inferred_params[0],
+                &[],
+                inferred_params,
+                false,
+            );
+        }
 
         self.complain_about_missing_type_params(
             missing_type_params,

src/librustc_typeck/collect.rs

@@ -320,7 +320,7 @@ impl AstConv<'tcx> for ItemCtxt<'tcx> {
     }
 
     fn ty_infer(&self, _: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
-        placeholder_type_error(self.tcx(), span, &[], vec![span], false);
+        self.tcx().sess.delay_span_bug(span, "bad placeholder type");
         self.tcx().types.err
     }
 
@@ -715,13 +715,21 @@ fn convert_trait_item(tcx: TyCtxt<'_>, trait_item_id: hir::HirId) {
     tcx.generics_of(def_id);
 
     match trait_item.kind {
-        hir::TraitItemKind::Const(..)
-        | hir::TraitItemKind::Type(_, Some(_))
-        | hir::TraitItemKind::Method(..) => {
+        hir::TraitItemKind::Method(..) => {
             tcx.type_of(def_id);
-            if let hir::TraitItemKind::Method(..) = trait_item.kind {
-                tcx.fn_sig(def_id);
-            }
+            tcx.fn_sig(def_id);
+        }
+
+        hir::TraitItemKind::Const(.., Some(_)) => {
+            tcx.type_of(def_id);
+        }
+
+        hir::TraitItemKind::Const(..) | hir::TraitItemKind::Type(_, Some(_)) => {
+            tcx.type_of(def_id);
+            // Account for `const C: _;` and `type T = _;`.
+            let mut visitor = PlaceholderHirTyCollector::default();
+            visitor.visit_trait_item(trait_item);
+            placeholder_type_error(tcx, DUMMY_SP, &[], visitor.0, false);
         }
 
         hir::TraitItemKind::Type(_, None) => {}
@@ -735,8 +743,18 @@ fn convert_impl_item(tcx: TyCtxt<'_>, impl_item_id: hir::HirId) {
     tcx.generics_of(def_id);
     tcx.type_of(def_id);
     tcx.predicates_of(def_id);
-    if let hir::ImplItemKind::Method(..) = tcx.hir().expect_impl_item(impl_item_id).kind {
-        tcx.fn_sig(def_id);
+    let impl_item = tcx.hir().expect_impl_item(impl_item_id);
+    match impl_item.kind {
+        hir::ImplItemKind::Method(..) => {
+            tcx.fn_sig(def_id);
+        }
+        hir::ImplItemKind::TyAlias(_) | hir::ImplItemKind::OpaqueTy(_) => {
+            // Account for `type T = _;`
+            let mut visitor = PlaceholderHirTyCollector::default();
+            visitor.visit_impl_item(impl_item);
+            placeholder_type_error(tcx, DUMMY_SP, &[], visitor.0, false);
+        }
+        hir::ImplItemKind::Const(..) => {}
     }
 }
 

src/test/ui/did_you_mean/bad-assoc-ty.rs

@@ -17,7 +17,6 @@ type D = (u8, u8)::AssocTy;
 type E = _::AssocTy;
 //~^ ERROR missing angle brackets in associated item path
 //~| ERROR the type placeholder `_` is not allowed within types on item signatures
-//~| ERROR the type placeholder `_` is not allowed within types on item signatures
 
 type F = &'static (u8)::AssocTy;
 //~^ ERROR missing angle brackets in associated item path
@@ -46,4 +45,8 @@ type I = ty!()::AssocTy;
 //~^ ERROR missing angle brackets in associated item path
 //~| ERROR ambiguous associated type
 
+trait K<A, B> {}
+fn foo<X: K<_, _>>(x: X) {}
+//~^ ERROR the type placeholder `_` is not allowed within types on item signatures
+
 fn main() {}

src/test/ui/did_you_mean/bad-assoc-ty.stderr

@@ -29,25 +29,25 @@ LL | type E = _::AssocTy;
    |          ^^^^^^^^^^ help: try: `<_>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:22:19
+  --> $DIR/bad-assoc-ty.rs:21:19
    |
 LL | type F = &'static (u8)::AssocTy;
    |                   ^^^^^^^^^^^^^ help: try: `<(u8)>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:28:10
+  --> $DIR/bad-assoc-ty.rs:27:10
    |
 LL | type G = dyn 'static + (Send)::AssocTy;
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `<dyn 'static + (Send)>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:45:10
+  --> $DIR/bad-assoc-ty.rs:44:10
    |
 LL | type I = ty!()::AssocTy;
    |          ^^^^^^^^^^^^^^ help: try: `<ty!()>::AssocTy`
 
 error: missing angle brackets in associated item path
-  --> $DIR/bad-assoc-ty.rs:38:19
+  --> $DIR/bad-assoc-ty.rs:37:19
    |
 LL |     ($ty: ty) => ($ty::AssocTy);
    |                   ^^^^^^^^^^^^ help: try: `<$ty>::AssocTy`
@@ -87,32 +87,26 @@ error[E0121]: the type placeholder `_` is not allowed within types on item signa
 LL | type E = _::AssocTy;
    |          ^ not allowed in type signatures
 
-error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/bad-assoc-ty.rs:17:10
-   |
-LL | type E = _::AssocTy;
-   |          ^ not allowed in type signatures
-
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:22:19
+  --> $DIR/bad-assoc-ty.rs:21:19
    |
 LL | type F = &'static (u8)::AssocTy;
    |                   ^^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:28:10
+  --> $DIR/bad-assoc-ty.rs:27:10
    |
 LL | type G = dyn 'static + (Send)::AssocTy;
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(dyn std::marker::Send + 'static) as Trait>::AssocTy`
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:34:10
+  --> $DIR/bad-assoc-ty.rs:33:10
    |
 LL | type H = Fn(u8) -> (u8)::Output;
    |          ^^^^^^^^^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<(dyn std::ops::Fn(u8) -> u8 + 'static) as Trait>::Output`
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:38:19
+  --> $DIR/bad-assoc-ty.rs:37:19
    |
 LL |     ($ty: ty) => ($ty::AssocTy);
    |                   ^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
@@ -123,11 +117,19 @@ LL | type J = ty!(u8);
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0223]: ambiguous associated type
-  --> $DIR/bad-assoc-ty.rs:45:10
+  --> $DIR/bad-assoc-ty.rs:44:10
    |
 LL | type I = ty!()::AssocTy;
    |          ^^^^^^^^^^^^^^ help: use fully-qualified syntax: `<u8 as Trait>::AssocTy`
 
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/bad-assoc-ty.rs:49:13
+   |
+LL | fn foo<X: K<_, _>>(x: X) {}
+   |             ^  ^ not allowed in type signatures
+   |             |
+   |             not allowed in type signatures
+
 error: aborting due to 20 previous errors
 
 Some errors have detailed explanations: E0121, E0223.

src/test/ui/self/self-infer.rs

@@ -2,9 +2,7 @@ struct S;
 
 impl S {
     fn f(self: _) {} //~ERROR the type placeholder `_` is not allowed within types on item sig
-    //~^ ERROR the type placeholder `_` is not allowed within types on item sig
     fn g(self: &_) {} //~ERROR the type placeholder `_` is not allowed within types on item sig
-    //~^ ERROR the type placeholder `_` is not allowed within types on item sig
 }
 
 fn main() {}

src/test/ui/self/self-infer.stderr

@@ -1,9 +1,3 @@
-error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/self-infer.rs:4:16
-   |
-LL |     fn f(self: _) {}
-   |                ^ not allowed in type signatures
-
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
   --> $DIR/self-infer.rs:4:16
    |
@@ -16,13 +10,7 @@ LL |     fn f<T>(self: T) {}
    |         ^^^       ^
 
 error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/self-infer.rs:6:17
-   |
-LL |     fn g(self: &_) {}
-   |                 ^ not allowed in type signatures
-
-error[E0121]: the type placeholder `_` is not allowed within types on item signatures
-  --> $DIR/self-infer.rs:6:17
+  --> $DIR/self-infer.rs:5:17
    |
 LL |     fn g(self: &_) {}
    |                 ^ not allowed in type signatures
@@ -32,6 +20,6 @@ help: use type parameters instead
 LL |     fn g<T>(self: &T) {}
    |         ^^^        ^
 
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0121`.