Rollup merge of #103621 - fee1-dead-contrib:iat-fix-use, r=cjgillot

Correctly resolve Inherent Associated Types

I don't know if this is the best way to do this, but at least it is one way.

Author: Dylan-DPC

Diff for: compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -1910,6 +1910,20 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
                     }
                 }
             }
+
+            // see if we can satisfy using an inherent associated type
+            for impl_ in tcx.inherent_impls(adt_def.did()) {
+                let assoc_ty = tcx.associated_items(impl_).find_by_name_and_kind(
+                    tcx,
+                    assoc_ident,
+                    ty::AssocKind::Type,
+                    *impl_,
+                );
+                if let Some(assoc_ty) = assoc_ty {
+                    let ty = tcx.type_of(assoc_ty.def_id);
+                    return Ok((ty, DefKind::AssocTy, assoc_ty.def_id));
+                }
+            }
         }
 
         // Find the type of the associated item, and the trait where the associated

Diff for: src/librustdoc/clean/mod.rs

@@ -1381,7 +1381,8 @@ fn clean_qpath<'tcx>(hir_ty: &hir::Ty<'tcx>, cx: &mut DocContext<'tcx>) -> Type
                 ty::Projection(proj) => Res::Def(DefKind::Trait, proj.trait_ref(cx.tcx).def_id),
                 // Rustdoc handles `ty::Error`s by turning them into `Type::Infer`s.
                 ty::Error(_) => return Type::Infer,
-                _ => bug!("clean: expected associated type, found `{:?}`", ty),
+                // Otherwise, this is an inherent associated type.
+                _ => return clean_middle_ty(ty, cx, None),
             };
             let trait_ = clean_path(&hir::Path { span, res, segments: &[] }, cx);
             register_res(cx, trait_.res);

Diff for: src/test/rustdoc-ui/ambiguous-inherent-assoc-ty.rs

@@ -1,3 +1,4 @@
+// check-pass
 // This test ensures that rustdoc does not panic on inherented associated types
 // that are referred to without fully-qualified syntax.
 
@@ -9,8 +10,4 @@ pub struct Struct;
 impl Struct {
     pub type AssocTy = usize;
     pub const AssocConst: Self::AssocTy = 42;
-    //~^ ERROR ambiguous associated type
-    //~| HELP use fully-qualified syntax
-    //~| ERROR ambiguous associated type
-    //~| HELP use fully-qualified syntax
 }

Diff for: src/test/rustdoc-ui/ambiguous-inherent-assoc-ty.stderr

@@ -0,0 +1,10 @@
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+struct Foo;
+
+impl Foo {
+    type Baz; //~ ERROR associated type in `impl` without body
+}
+
+fn main() {}

Diff for: src/test/ui/assoc-inherent.rs

@@ -0,0 +1,10 @@
+error: associated type in `impl` without body
+  --> $DIR/assoc-inherent-no-body.rs:7:5
+   |
+LL |     type Baz;
+   |     ^^^^^^^^-
+   |             |
+   |             help: provide a definition for the type: `= <type>;`
+
+error: aborting due to previous error
+

Diff for: src/test/ui/assoc-inherent.stderr

@@ -0,0 +1,14 @@
+// check-pass
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+struct Foo;
+
+impl Foo {
+    type Bar = isize;
+}
+
+fn main() {
+    let x: Foo::Bar;
+    x = 0isize;
+}

Diff for: src/test/ui/associated-inherent-types/assoc-inherent-no-body.rs

@@ -1,40 +1,40 @@
 error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:14:13
+  --> $DIR/resolve-self-in-impl.rs:16:6
    |
-LL | impl Tr for Self {}
-   |             ^^^^
+LL | impl Self {}
+   |      ^^^^
    |
    = note: replace `Self` with a different type
 
 error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:15:15
+  --> $DIR/resolve-self-in-impl.rs:17:8
    |
-LL | impl Tr for S<Self> {}
-   |               ^^^^
+LL | impl S<Self> {}
+   |        ^^^^
    |
    = note: replace `Self` with a different type
 
 error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:16:6
+  --> $DIR/resolve-self-in-impl.rs:18:7
    |
-LL | impl Self {}
-   |      ^^^^
+LL | impl (Self, Self) {}
+   |       ^^^^  ^^^^
    |
    = note: replace `Self` with a different type
 
 error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:17:8
+  --> $DIR/resolve-self-in-impl.rs:14:13
    |
-LL | impl S<Self> {}
-   |        ^^^^
+LL | impl Tr for Self {}
+   |             ^^^^
    |
    = note: replace `Self` with a different type
 
 error: `Self` is not valid in the self type of an impl block
-  --> $DIR/resolve-self-in-impl.rs:18:7
+  --> $DIR/resolve-self-in-impl.rs:15:15
    |
-LL | impl (Self, Self) {}
-   |       ^^^^  ^^^^
+LL | impl Tr for S<Self> {}
+   |               ^^^^
    |
    = note: replace `Self` with a different type