Review changes

compiler/rustc_ast/src/ast.rs

@@ -2666,6 +2666,18 @@ pub struct Trait {
 /// a `where` keyword (`bool`). This is split out from `WhereClause`, since there
 /// are two locations for where clause on type aliases, but their predicates
 /// are concatenated together.
+///
+/// Take this example:
+/// ```rust, ignore
+/// trait Foo {
+///   type Assoc<'a, 'b> where Self: 'a, Self: 'b;
+/// }
+/// impl Foo for () {
+///   type Assoc<'a, 'b> where Self: 'a = () where Self: 'b;
+///   //                 ^^^^^^^^^^^^^^ first where clause
+///   //                                     ^^^^^^^^^^^^^^ second where clause
+/// }
+/// ```
 #[derive(Copy, Clone, Encodable, Decodable, Debug, Default)]
 pub struct TyAliasWhereClause(pub bool, pub Span);
 

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1275,10 +1275,14 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 }
                 self.check_type_no_bounds(bounds, "this context");
                 if where_clauses.1.0 {
-                    self.err_handler().span_err(
+                    let mut err = self.err_handler().struct_span_err(
                         where_clauses.1.1,
                         "where clauses are not allowed after the type for type aliases",
-                    )
+                    );
+                    err.note(
+                        "see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information",
+                    );
+                    err.emit();
                 }
             }
             _ => {}

compiler/rustc_lint/src/context.rs

@@ -819,12 +819,14 @@ pub trait LintContext: Sized {
                     }
                 },
                 BuiltinLintDiagnostics::DeprecatedWhereclauseLocation(new_span, suggestion) => {
-                    db.span_suggestion(
+                    db.multipart_suggestion(
-                        new_span,
+                        "move it to the end of the type declaration",
-                        "move it here",
+                        vec![(db.span.primary_span().unwrap(), "".to_string()), (new_span, suggestion)],
-                        suggestion,
                         Applicability::MachineApplicable,
                     );
+                    db.note(
+                        "see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information",
+                    );
                 },
             }
             // Rewrap `db`, and pass control to the user.

src/test/ui/parser/type-alias-where-fixable.fixed

@@ -0,0 +1,30 @@
+// check-pass
+// run-rustfix
+
+#![feature(generic_associated_types)]
+
+trait Trait {
+    // Fine.
+    type Assoc where u32: Copy;
+    // Fine.
+    type Assoc2 where u32: Copy, i32: Copy;
+}
+
+impl Trait for u32 {
+    // Not fine, suggests moving.
+    type Assoc  = () where u32: Copy;
+    //~^ WARNING where clause not allowed here
+    // Not fine, suggests moving `u32: Copy`
+    type Assoc2  = () where i32: Copy, u32: Copy;
+    //~^ WARNING where clause not allowed here
+}
+
+impl Trait for i32 {
+    // Fine.
+    type Assoc = () where u32: Copy;
+    // Not fine, suggests moving both.
+    type Assoc2  = () where u32: Copy, i32: Copy;
+    //~^ WARNING where clause not allowed here
+}
+
+fn main() {}

src/test/ui/parser/type-alias-where-fixable.rs

@@ -0,0 +1,30 @@
+// check-pass
+// run-rustfix
+
+#![feature(generic_associated_types)]
+
+trait Trait {
+    // Fine.
+    type Assoc where u32: Copy;
+    // Fine.
+    type Assoc2 where u32: Copy, i32: Copy;
+}
+
+impl Trait for u32 {
+    // Not fine, suggests moving.
+    type Assoc where u32: Copy = ();
+    //~^ WARNING where clause not allowed here
+    // Not fine, suggests moving `u32: Copy`
+    type Assoc2 where u32: Copy = () where i32: Copy;
+    //~^ WARNING where clause not allowed here
+}
+
+impl Trait for i32 {
+    // Fine.
+    type Assoc = () where u32: Copy;
+    // Not fine, suggests moving both.
+    type Assoc2 where u32: Copy, i32: Copy = ();
+    //~^ WARNING where clause not allowed here
+}
+
+fn main() {}

src/test/ui/parser/type-alias-where-fixable.stderr

@@ -0,0 +1,42 @@
+warning: where clause not allowed here
+  --> $DIR/type-alias-where-fixable.rs:15:16
+   |
+LL |     type Assoc where u32: Copy = ();
+   |                ^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(deprecated_where_clause_location)]` on by default
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+help: move it to the end of the type declaration
+   |
+LL -     type Assoc where u32: Copy = ();
+LL +     type Assoc  = () where u32: Copy;
+   | 
+
+warning: where clause not allowed here
+  --> $DIR/type-alias-where-fixable.rs:18:17
+   |
+LL |     type Assoc2 where u32: Copy = () where i32: Copy;
+   |                 ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+help: move it to the end of the type declaration
+   |
+LL -     type Assoc2 where u32: Copy = () where i32: Copy;
+LL +     type Assoc2  = () where i32: Copy, u32: Copy;
+   | 
+
+warning: where clause not allowed here
+  --> $DIR/type-alias-where-fixable.rs:26:17
+   |
+LL |     type Assoc2 where u32: Copy, i32: Copy = ();
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
+help: move it to the end of the type declaration
+   |
+LL -     type Assoc2 where u32: Copy, i32: Copy = ();
+LL +     type Assoc2  = () where u32: Copy, i32: Copy;
+   | 
+
+warning: 3 warnings emitted
+

src/test/ui/parser/type-alias-where.rs

@@ -10,28 +10,4 @@ type Bar = () where u32: Copy;
 type Baz = () where;
 //~^ ERROR where clauses are not allowed
 
-trait Trait {
-    // Fine.
-    type Assoc where u32: Copy;
-    // Fine.
-    type Assoc2 where u32: Copy, i32: Copy;
-}
-
-impl Trait for u32 {
-    // Not fine, suggests moving.
-    type Assoc where u32: Copy = ();
-    //~^ WARNING where clause not allowed here
-    // Not fine, suggests moving `u32: Copy`
-    type Assoc2 where u32: Copy = () where i32: Copy;
-    //~^ WARNING where clause not allowed here
-}
-
-impl Trait for i32 {
-    // Fine.
-    type Assoc = () where u32: Copy;
-    // Not fine, suggests moving both.
-    type Assoc2 where u32: Copy, i32: Copy = ();
-    //~^ WARNING where clause not allowed here
-}
-
 fn main() {}

src/test/ui/parser/type-alias-where.stderr

@@ -3,32 +3,16 @@ error: where clauses are not allowed after the type for type aliases
    |
 LL | type Bar = () where u32: Copy;
    |               ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
 
 error: where clauses are not allowed after the type for type aliases
   --> $DIR/type-alias-where.rs:10:15
    |
 LL | type Baz = () where;
    |               ^^^^^
-
-warning: where clause not allowed here
-  --> $DIR/type-alias-where.rs:22:16
    |
-LL |     type Assoc where u32: Copy = ();
+   = note: see issue #89122 <https://github.com/rust-lang/rust/issues/89122> for more information
-   |                ^^^^^^^^^^^^^^^     - help: move it here: `where u32: Copy`
-   |
-   = note: `#[warn(deprecated_where_clause_location)]` on by default
 
-warning: where clause not allowed here
+error: aborting due to 2 previous errors
-  --> $DIR/type-alias-where.rs:25:17
-   |
-LL |     type Assoc2 where u32: Copy = () where i32: Copy;
-   |                 ^^^^^^^^^^^^^^^                     - help: move it here: `, u32: Copy`
-
-warning: where clause not allowed here
-  --> $DIR/type-alias-where.rs:33:17
-   |
-LL |     type Assoc2 where u32: Copy, i32: Copy = ();
-   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^     - help: move it here: `where u32: Copy, i32: Copy`
-
-error: aborting due to 2 previous errors; 3 warnings emitted