Move the "matches no value" note to be a span label

Author: Nadrieril

compiler/rustc_mir_build/messages.ftl

@@ -333,7 +333,7 @@ mir_build_unreachable_matches_same_values = matches some of the same values
 
 mir_build_unreachable_pattern = unreachable pattern
     .label = no value can reach this
-    .unreachable_matches_no_values = matches no values because `{$ty}` is uninhabited
+    .unreachable_matches_no_values = matches no values because `{$matches_no_values_ty}` is uninhabited
     .unreachable_uninhabited_note = to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
     .unreachable_covered_by_catchall = matches any value
     .unreachable_covered_by_one = matches all the relevant values

compiler/rustc_mir_build/src/errors.rs

@@ -586,8 +586,9 @@ pub(crate) struct NonConstPath {
 pub(crate) struct UnreachablePattern<'tcx> {
     #[label]
     pub(crate) span: Option<Span>,
-    #[subdiagnostic]
-    pub(crate) matches_no_values: Option<UnreachableMatchesNoValues<'tcx>>,
+    #[label(mir_build_unreachable_matches_no_values)]
+    pub(crate) matches_no_values: Option<Span>,
+    pub(crate) matches_no_values_ty: Ty<'tcx>,
     #[note(mir_build_unreachable_uninhabited_note)]
     pub(crate) uninhabited_note: Option<()>,
     #[label(mir_build_unreachable_covered_by_catchall)]
@@ -599,12 +600,6 @@ pub(crate) struct UnreachablePattern<'tcx> {
     pub(crate) covered_by_many_n_more_count: usize,
 }
 
-#[derive(Subdiagnostic)]
-#[note(mir_build_unreachable_matches_no_values)]
-pub(crate) struct UnreachableMatchesNoValues<'tcx> {
-    pub(crate) ty: Ty<'tcx>,
-}
-
 #[derive(Diagnostic)]
 #[diag(mir_build_const_pattern_depends_on_generic_parameter, code = E0158)]
 pub(crate) struct ConstPatternDependsOnGenericParameter {

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -922,6 +922,7 @@ fn report_unreachable_pattern<'p, 'tcx>(
     let mut lint = UnreachablePattern {
         span: Some(pat_span),
         matches_no_values: None,
+        matches_no_values_ty: **pat.ty(),
         uninhabited_note: None,
         covered_by_catchall: None,
         covered_by_one: None,
@@ -933,10 +934,11 @@ fn report_unreachable_pattern<'p, 'tcx>(
             // Empty pattern; we report the uninhabited type that caused the emptiness.
             lint.span = None; // Don't label the pattern itself
             lint.uninhabited_note = Some(()); // Give a link about empty types
+            lint.matches_no_values = Some(pat_span);
             pat.walk(&mut |subpat| {
                 let ty = **subpat.ty();
                 if cx.is_uninhabited(ty) {
-                    lint.matches_no_values = Some(UnreachableMatchesNoValues { ty });
+                    lint.matches_no_values_ty = ty;
                     false // No need to dig further.
                 } else if matches!(subpat.ctor(), Constructor::Ref | Constructor::UnionField) {
                     false // Don't explore further since they are not by-value.

tests/ui/pattern/usefulness/empty-match-check-notes.exhaustive_patterns.stderr

@@ -2,9 +2,8 @@ error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:17:9
    |
 LL |         _ => {}
-   |         ^
+   |         ^ matches no values because `EmptyEnum` is uninhabited
    |
-   = note: matches no values because `EmptyEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 note: the lint level is defined here
   --> $DIR/empty-match-check-notes.rs:7:9
@@ -16,27 +15,24 @@ error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:22:9
    |
 LL |         _ if false => {}
-   |         ^
+   |         ^ matches no values because `EmptyEnum` is uninhabited
    |
-   = note: matches no values because `EmptyEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 
 error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:31:9
    |
 LL |         _ => {}
-   |         ^
+   |         ^ matches no values because `EmptyForeignEnum` is uninhabited
    |
-   = note: matches no values because `EmptyForeignEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 
 error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:36:9
    |
 LL |         _ if false => {}
-   |         ^
+   |         ^ matches no values because `EmptyForeignEnum` is uninhabited
    |
-   = note: matches no values because `EmptyForeignEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 
 error[E0005]: refutable pattern in local binding

tests/ui/pattern/usefulness/empty-match-check-notes.normal.stderr

@@ -2,9 +2,8 @@ error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:17:9
    |
 LL |         _ => {}
-   |         ^
+   |         ^ matches no values because `EmptyEnum` is uninhabited
    |
-   = note: matches no values because `EmptyEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 note: the lint level is defined here
   --> $DIR/empty-match-check-notes.rs:7:9
@@ -16,27 +15,24 @@ error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:22:9
    |
 LL |         _ if false => {}
-   |         ^
+   |         ^ matches no values because `EmptyEnum` is uninhabited
    |
-   = note: matches no values because `EmptyEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 
 error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:31:9
    |
 LL |         _ => {}
-   |         ^
+   |         ^ matches no values because `EmptyForeignEnum` is uninhabited
    |
-   = note: matches no values because `EmptyForeignEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 
 error: unreachable pattern
   --> $DIR/empty-match-check-notes.rs:36:9
    |
 LL |         _ if false => {}
-   |         ^
+   |         ^ matches no values because `EmptyForeignEnum` is uninhabited
    |
-   = note: matches no values because `EmptyForeignEnum` is uninhabited
    = note: to learn more about uninhabited types, see https://doc.rust-lang.org/nomicon/exotic-sizes.html#empty-types
 
 error[E0005]: refutable pattern in local binding