Make recovery for enum with struct field a bit more accurate

Author: compiler-errors

compiler/rustc_parse/src/parser/item.rs

@@ -1552,7 +1552,8 @@ impl<'a> Parser<'a> {
             })
             .map_err(|mut err| {
                 err.span_label(ident.span, "while parsing this enum");
-                if self.token == token::Colon {
+                // Try to recover `enum Foo { ident : Ty }`.
+                if self.prev_token.is_non_reserved_ident() && self.token == token::Colon {
                     let snapshot = self.create_snapshot_for_diagnostic();
                     self.bump();
                     match self.parse_ty() {

tests/ui/structs-enums/recover-enum-with-bad-where.rs

@@ -0,0 +1,6 @@
+pub enum Foo<T>
+where:
+//~^ ERROR expected one of `#`, `{`, lifetime, or type, found `:`
+    T: Missing, {}
+
+fn main() {}

tests/ui/structs-enums/recover-enum-with-bad-where.stderr

@@ -0,0 +1,10 @@
+error: expected one of `#`, `{`, lifetime, or type, found `:`
+  --> $DIR/recover-enum-with-bad-where.rs:2:6
+   |
+LL | pub enum Foo<T>
+   |          --- while parsing this enum
+LL | where:
+   |      ^ expected one of `#`, `{`, lifetime, or type
+
+error: aborting due to 1 previous error
+