adjust enum type instead of variant suggestions for prelude enums

The present author regrets not thinking of a more eloquent way to do
this.

Author: zackmdavis

src/librustc_resolve/lib.rs

@@ -3237,7 +3237,17 @@ impl<'a> Resolver<'a> {
                     err.span_suggestions_with_applicability(
                         span,
                         &msg,
-                        enum_candidates.into_iter().map(|(_variant, enum_ty)| enum_ty),
+                        enum_candidates.into_iter()
+                            .map(|(_variant_path, enum_ty_path)| enum_ty_path)
+                            // variants reëxported in prelude doesn't mean `prelude::v1` is the
+                            // type name! FIXME: is there a more principled way to do this that
+                            // would work for other reëxports?
+                            .filter(|enum_ty_path| enum_ty_path != "std::prelude::v1")
+                            // also say `Option` rather than `std::prelude::v1::Option`
+                            .map(|enum_ty_path| {
+                                // FIXME #56861: DRYer prelude filtering
+                                enum_ty_path.trim_start_matches("std::prelude::v1::").to_owned()
+                            }),
                         Applicability::MachineApplicable,
                     );
                 }

src/librustc_typeck/check/demand.rs

@@ -123,6 +123,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                         let sole_field_ty = sole_field.ty(self.tcx, substs);
                         if self.can_coerce(expr_ty, sole_field_ty) {
                             let variant_path = self.tcx.item_path_str(variant.did);
+                            // FIXME #56861: DRYer prelude filtering
                             Some(variant_path.trim_start_matches("std::prelude::v1::").to_string())
                         } else {
                             None

src/test/ui/did_you_mean/issue-56028-there-is-an-enum-variant.rs

@@ -7,6 +7,8 @@ enum Solidify { Set }
 enum UnorderedCollection { Set }
 
 fn setup() -> Set { Set }
+//~^ ERROR cannot find type `Set` in this scope
+//~| ERROR cannot find value `Set` in this scope
 
 fn main() {
     setup();

src/test/ui/issues/issue-35675.stderr

@@ -41,13 +41,10 @@ error[E0573]: expected type, found variant `Ok`
   --> $DIR/issue-35675.rs:29:13
    |
 LL | fn foo() -> Ok {
-   |             ^^ not a type
-help: try using the variant's enum
-   |
-LL | fn foo() -> std::prelude::v1 {
-   |             ^^^^^^^^^^^^^^^^
-LL | fn foo() -> std::result::Result {
-   |             ^^^^^^^^^^^^^^^^^^^
+   |             ^^
+   |             |
+   |             not a type
+   |             help: try using the variant's enum: `std::result::Result`
 
 error[E0412]: cannot find type `Variant3` in this scope
   --> $DIR/issue-35675.rs:34:13
@@ -63,13 +60,10 @@ error[E0573]: expected type, found variant `Some`
   --> $DIR/issue-35675.rs:38:13
    |
 LL | fn qux() -> Some {
-   |             ^^^^ not a type
-help: try using the variant's enum
-   |
-LL | fn qux() -> std::prelude::v1::Option {
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^
-LL | fn qux() -> std::prelude::v1 {
-   |             ^^^^^^^^^^^^^^^^
+   |             ^^^^
+   |             |
+   |             not a type
+   |             help: try using the variant's enum: `Option`
 
 error: aborting due to 7 previous errors