Rollup merge of #92118 - jackh726:type-alias-position-error, r=petrochenkov

Parse and suggest moving where clauses after equals for type aliases

~Mostly the same as #90076, but doesn't make any syntax changes.~ Whether or not we want to land the syntax changes, we should  parse the invalid where clause position and suggest moving.

r? `@nikomatsakis`
cc `@petrochenkov` you might have thoughts on implementation

2 files changed, 77 insertions, 0 deletions

diff --git a/src/test/ui/parser/type-alias-where.rs b/src/test/ui/parser/type-alias-where.rs
new file mode 100644
index 00000000000..a9fa23dd95e
--- /dev/null
+++ b/src/test/ui/parser/type-alias-where.rs
@@ -0,0 +1,37 @@
+// check-fail
+
+#![feature(generic_associated_types)]
+
+// Fine, but lints as unused
+type Foo where u32: Copy = ();
+// Not fine.
+type Bar = () where u32: Copy;
+//~^ ERROR where clause not allowed here
+type Baz = () where;
+//~^ ERROR where clause not allowed here
+
+trait Trait {
+    // Fine.
+    type Assoc where u32: Copy;
+    // Fine.
+    type Assoc2 where u32: Copy, i32: Copy;
+}
+
+impl Trait for u32 {
+    // Fine.
+    type Assoc where u32: Copy = ();
+    // Not fine, suggests moving `i32: Copy`
+    type Assoc2 where u32: Copy = () where i32: Copy;
+    //~^ ERROR where clause not allowed here
+}
+
+impl Trait for i32 {
+    // Not fine, suggests moving `u32: Copy`
+    type Assoc = () where u32: Copy;
+    //~^ ERROR where clause not allowed here
+    // Not fine, suggests moving both.
+    type Assoc2 = () where u32: Copy, i32: Copy;
+    //~^ ERROR where clause not allowed here
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/type-alias-where.stderr b/src/test/ui/parser/type-alias-where.stderr
new file mode 100644
index 00000000000..7ab0b28c864
--- /dev/null
+++ b/src/test/ui/parser/type-alias-where.stderr
@@ -0,0 +1,40 @@
+error: where clause not allowed here
+  --> $DIR/type-alias-where.rs:8:15
+   |
+LL | type Bar = () where u32: Copy;
+   |         -     ^^^^^^^^^^^^^^^
+   |         |
+   |         help: move it here: `where u32: Copy`
+
+error: where clause not allowed here
+  --> $DIR/type-alias-where.rs:10:15
+   |
+LL | type Baz = () where;
+   |               ^^^^^
+
+error: where clause not allowed here
+  --> $DIR/type-alias-where.rs:24:38
+   |
+LL |     type Assoc2 where u32: Copy = () where i32: Copy;
+   |                                -     ^^^^^^^^^^^^^^^
+   |                                |
+   |                                help: move it here: `, i32: Copy`
+
+error: where clause not allowed here
+  --> $DIR/type-alias-where.rs:30:21
+   |
+LL |     type Assoc = () where u32: Copy;
+   |               -     ^^^^^^^^^^^^^^^
+   |               |
+   |               help: move it here: `where u32: Copy`
+
+error: where clause not allowed here
+  --> $DIR/type-alias-where.rs:33:22
+   |
+LL |     type Assoc2 = () where u32: Copy, i32: Copy;
+   |                -     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                |
+   |                help: move it here: `where u32: Copy, i32: Copy`
+
+error: aborting due to 5 previous errors
+