move suggestions to its own method

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -250,25 +250,8 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         let code = source.error_code(res.is_some());
         let mut err =
             self.r.session.struct_span_err_with_code(base_error.span, &base_error.msg, code);
-        if let Some((trait_ref, self_ty)) =
+
-            self.diagnostic_metadata.currently_processing_impl_trait.clone()
+        self.suggest_swapping_misplaced_self_ty_and_trait(&mut err, source, res, base_error.span);
-            && let TyKind::Path(_, self_ty_path) = &self_ty.kind
-            && let PathResult::Module(ModuleOrUniformRoot::Module(module)) = self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
-            && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
-            && trait_ref.path.span == span
-            && let PathSource::Trait(_) = source
-            && let Some(Res::Def(DefKind::Struct, _)) = res
-            && let Ok(self_ty_str) =
-                self.r.session.source_map().span_to_snippet(self_ty.span)
-            && let Ok(trait_ref_str) =
-                self.r.session.source_map().span_to_snippet(trait_ref.path.span)
-        {
-                err.multipart_suggestion(
-                    "consider swapping the struct and the trait",
-                    vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
-                    Applicability::MaybeIncorrect,
-                );
-        }
 
         if let Some(sugg) = base_error.suggestion {
             err.span_suggestion_verbose(sugg.0, sugg.1, sugg.2, Applicability::MaybeIncorrect);
@@ -704,6 +687,35 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         }
     }
 
+    fn suggest_swapping_misplaced_self_ty_and_trait(
+        &mut self,
+        err: &mut Diagnostic,
+        source: PathSource<'_>,
+        res: Option<Res>,
+        span: Span,
+    ) {
+        if let Some((trait_ref, self_ty)) =
+            self.diagnostic_metadata.currently_processing_impl_trait.clone()
+            && let TyKind::Path(_, self_ty_path) = &self_ty.kind
+            && let PathResult::Module(ModuleOrUniformRoot::Module(module)) =
+                self.resolve_path(&Segment::from_path(self_ty_path), Some(TypeNS), None)
+            && let ModuleKind::Def(DefKind::Trait, ..) = module.kind
+            && trait_ref.path.span == span
+            && let PathSource::Trait(_) = source
+            && let Some(Res::Def(DefKind::Struct | DefKind::Enum | DefKind::Union, _)) = res
+            && let Ok(self_ty_str) =
+                self.r.session.source_map().span_to_snippet(self_ty.span)
+            && let Ok(trait_ref_str) =
+                self.r.session.source_map().span_to_snippet(trait_ref.path.span)
+        {
+                err.multipart_suggestion(
+                    "`impl` items mention the trait being implemented first and the type it is being implemented for second",
+                    vec![(trait_ref.path.span, self_ty_str), (self_ty.span, trait_ref_str)],
+                    Applicability::MaybeIncorrect,
+                );
+        }
+    }
+
     fn get_single_associated_item(
         &mut self,
         path: &[Segment],

src/test/ui/suggestions/suggest-swapping-self-ty-and-trait-edition-2021.rs

@@ -2,10 +2,21 @@
 
 pub trait Trait<'a, T> {}
 
-pub struct Struct<T> {}
+pub struct Struct<T>;
+pub enum Enum<T> {}
+
+pub union Union<T> {
+    f1: usize,
+}
 
 impl<'a, T> Struct<T> for Trait<'a, T> {}
 //~^ ERROR expected trait, found struct `Struct`
 //~| ERROR trait objects must include the `dyn` keyword
 
+impl<'a, T> Enum<T> for Trait<'a, T> {}
+//~^ ERROR expected trait, found enum `Enum`
+
+impl<'a, T> Union<T> for Trait<'a, T> {}
+//~^ ERROR expected trait, found union `Union`
+
 fn main() {}

src/test/ui/suggestions/suggest-swapping-self-ty-and-trait-edition-2021.stderr

@@ -1,16 +1,38 @@
 error[E0404]: expected trait, found struct `Struct`
-  --> $DIR/suggest-swapping-self-ty-and-trait-edition-2021.rs:7:13
+  --> $DIR/suggest-swapping-self-ty-and-trait-edition-2021.rs:12:13
    |
 LL | impl<'a, T> Struct<T> for Trait<'a, T> {}
    |             ^^^^^^^^^ not a trait
    |
-help: consider swapping the struct and the trait
+help: `impl` items mention the trait being implemented first and the type it is being implemented for second
    |
 LL | impl<'a, T> Trait<'a, T> for Struct<T> {}
    |             ~~~~~~~~~~~~     ~~~~~~~~~
 
+error[E0404]: expected trait, found enum `Enum`
+  --> $DIR/suggest-swapping-self-ty-and-trait-edition-2021.rs:16:13
+   |
+LL | impl<'a, T> Enum<T> for Trait<'a, T> {}
+   |             ^^^^^^^ not a trait
+   |
+help: `impl` items mention the trait being implemented first and the type it is being implemented for second
+   |
+LL | impl<'a, T> Trait<'a, T> for Enum<T> {}
+   |             ~~~~~~~~~~~~     ~~~~~~~
+
+error[E0404]: expected trait, found union `Union`
+  --> $DIR/suggest-swapping-self-ty-and-trait-edition-2021.rs:19:13
+   |
+LL | impl<'a, T> Union<T> for Trait<'a, T> {}
+   |             ^^^^^^^^ not a trait
+   |
+help: `impl` items mention the trait being implemented first and the type it is being implemented for second
+   |
+LL | impl<'a, T> Trait<'a, T> for Union<T> {}
+   |             ~~~~~~~~~~~~     ~~~~~~~~
+
 error[E0782]: trait objects must include the `dyn` keyword
-  --> $DIR/suggest-swapping-self-ty-and-trait-edition-2021.rs:7:27
+  --> $DIR/suggest-swapping-self-ty-and-trait-edition-2021.rs:12:27
    |
 LL | impl<'a, T> Struct<T> for Trait<'a, T> {}
    |                           ^^^^^^^^^^^^
@@ -21,7 +43,7 @@ LL - impl<'a, T> Struct<T> for Trait<'a, T> {}
 LL + impl<'a, T> Struct<T> for dyn Trait<'a, T> {}
    | 
 
-error: aborting due to 2 previous errors
+error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0404, E0782.
 For more information about an error, try `rustc --explain E0404`.

src/test/ui/suggestions/suggest-swapping-self-ty-and-trait.rs

@@ -1,10 +1,21 @@
 pub trait Trait<'a, T> {}
 
-pub struct Struct<T> {}
+pub struct Struct<T>;
+pub enum Enum<T> {}
+
+pub union Union<T> {
+    f1: usize,
+}
 
 impl<'a, T> Struct<T> for Trait<'a, T> {}
 //~^ ERROR expected trait, found struct `Struct`
 //~| WARNING trait objects without an explicit `dyn` are deprecated
 //~| WARNING this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
 
+impl<'a, T> Enum<T> for Trait<'a, T> {}
+//~^ ERROR expected trait, found enum `Enum`
+
+impl<'a, T> Union<T> for Trait<'a, T> {}
+//~^ ERROR expected trait, found union `Union`
+
 fn main() {}

src/test/ui/suggestions/suggest-swapping-self-ty-and-trait.stderr

@@ -1,16 +1,38 @@
 error[E0404]: expected trait, found struct `Struct`
-  --> $DIR/suggest-swapping-self-ty-and-trait.rs:5:13
+  --> $DIR/suggest-swapping-self-ty-and-trait.rs:10:13
    |
 LL | impl<'a, T> Struct<T> for Trait<'a, T> {}
    |             ^^^^^^^^^ not a trait
    |
-help: consider swapping the struct and the trait
+help: `impl` items mention the trait being implemented first and the type it is being implemented for second
    |
 LL | impl<'a, T> Trait<'a, T> for Struct<T> {}
    |             ~~~~~~~~~~~~     ~~~~~~~~~
 
+error[E0404]: expected trait, found enum `Enum`
+  --> $DIR/suggest-swapping-self-ty-and-trait.rs:15:13
+   |
+LL | impl<'a, T> Enum<T> for Trait<'a, T> {}
+   |             ^^^^^^^ not a trait
+   |
+help: `impl` items mention the trait being implemented first and the type it is being implemented for second
+   |
+LL | impl<'a, T> Trait<'a, T> for Enum<T> {}
+   |             ~~~~~~~~~~~~     ~~~~~~~
+
+error[E0404]: expected trait, found union `Union`
+  --> $DIR/suggest-swapping-self-ty-and-trait.rs:18:13
+   |
+LL | impl<'a, T> Union<T> for Trait<'a, T> {}
+   |             ^^^^^^^^ not a trait
+   |
+help: `impl` items mention the trait being implemented first and the type it is being implemented for second
+   |
+LL | impl<'a, T> Trait<'a, T> for Union<T> {}
+   |             ~~~~~~~~~~~~     ~~~~~~~~
+
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/suggest-swapping-self-ty-and-trait.rs:5:27
+  --> $DIR/suggest-swapping-self-ty-and-trait.rs:10:27
    |
 LL | impl<'a, T> Struct<T> for Trait<'a, T> {}
    |                           ^^^^^^^^^^^^
@@ -24,6 +46,6 @@ LL - impl<'a, T> Struct<T> for Trait<'a, T> {}
 LL + impl<'a, T> Struct<T> for dyn Trait<'a, T> {}
    | 
 
-error: aborting due to previous error; 1 warning emitted
+error: aborting due to 3 previous errors; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0404`.