Improve "covered_by_many" error

compiler/rustc_mir_build/messages.ftl

@@ -325,12 +325,16 @@ mir_build_union_field_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
 
 mir_build_union_pattern = cannot use unions in constant patterns
 
+mir_build_unreachable_making_this_unreachable = collectively making this unreachable
+
+mir_build_unreachable_matches_same_values = matches some of the same values
+
 mir_build_unreachable_pattern = unreachable pattern
     .label = unreachable pattern
     .unreachable_matches_no_values = this pattern matches no values because `{$ty}` is uninhabited
     .unreachable_covered_by_catchall = matches any value
     .unreachable_covered_by_one = matches all the values already
-    .unreachable_covered_by_many = matches some of the same values
+    .unreachable_covered_by_many = these patterns collectively make the last one unreachable
 
 mir_build_unsafe_fn_safe_body = an unsafe function restricts its caller, but its body is safe by default
 mir_build_unsafe_not_inherited = items do not inherit unsafety from separate enclosing items

compiler/rustc_mir_build/src/errors.rs

@@ -591,8 +591,8 @@ pub(crate) struct UnreachablePattern<'tcx> {
     pub(crate) covered_by_catchall: Option<Span>,
     #[label(mir_build_unreachable_covered_by_one)]
     pub(crate) covered_by_one: Option<Span>,
-    #[subdiagnostic]
-    pub(crate) covered_by_many: Option<UnreachableCoveredByMany>,
+    #[note(mir_build_unreachable_covered_by_many)]
+    pub(crate) covered_by_many: Option<MultiSpan>,
 }
 
 #[derive(Subdiagnostic)]
@@ -601,20 +601,6 @@ pub(crate) struct UnreachableMatchesNoValues<'tcx> {
     pub(crate) ty: Ty<'tcx>,
 }
 
-pub(crate) struct UnreachableCoveredByMany(pub(crate) Vec<Span>);
-
-impl Subdiagnostic for UnreachableCoveredByMany {
-    fn add_to_diag_with<G: EmissionGuarantee, F: SubdiagMessageOp<G>>(
-        self,
-        diag: &mut Diag<'_, G>,
-        _f: &F,
-    ) {
-        for span in self.0 {
-            diag.span_label(span, fluent::mir_build_unreachable_covered_by_many);
-        }
-    }
-}
-
 #[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

@@ -1,4 +1,5 @@
 use crate::errors::*;
+use crate::fluent_generated as fluent;
 
 use rustc_arena::{DroplessArena, TypedArena};
 use rustc_ast::Mutability;
@@ -944,8 +945,16 @@ fn report_unreachable_pattern<'p, 'tcx>(
             lint.covered_by_one = Some(covering_pat.data().span);
         }
         covering_pats => {
-            let covering_spans = covering_pats.iter().map(|p| p.data().span).collect();
-            lint.covered_by_many = Some(UnreachableCoveredByMany(covering_spans));
+            let mut multispan = MultiSpan::from_span(pat_span);
+            for p in covering_pats {
+                multispan.push_span_label(
+                    p.data().span,
+                    fluent::mir_build_unreachable_matches_same_values,
+                );
+            }
+            multispan
+                .push_span_label(pat_span, fluent::mir_build_unreachable_making_this_unreachable);
+            lint.covered_by_many = Some(multispan);
         }
     }
     cx.tcx.emit_node_span_lint(UNREACHABLE_PATTERNS, hir_id, pat_span, lint);

tests/ui/error-codes/E0001.stderr

@@ -1,13 +1,18 @@
 error: unreachable pattern
   --> $DIR/E0001.rs:8:9
    |
+LL |         _ => {/* ... */}
+   |         ^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/E0001.rs:8:9
+   |
 LL |         Some(_) => {/* ... */}
    |         ------- matches some of the same values
 LL |         None => {/* ... */}
    |         ---- matches some of the same values
 LL |         _ => {/* ... */}
-   |         ^ unreachable pattern
-   |
+   |         ^ collectively making this unreachable
 note: the lint level is defined here
   --> $DIR/E0001.rs:1:9
    |

tests/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr

@@ -23,12 +23,18 @@ LL |         (2,) => {}
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:19:9
    |
+LL |         (1 | 2,) => {}
+   |         ^^^^^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:19:9
+   |
 LL |         (1,) => {}
    |         ---- matches some of the same values
 LL |         (2,) => {}
    |         ---- matches some of the same values
 LL |         (1 | 2,) => {}
-   |         ^^^^^^^^ unreachable pattern
+   |         ^^^^^^^^ collectively making this unreachable
 
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:24:9
@@ -68,13 +74,19 @@ LL |         (2 | 1, 4) => {}
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:29:9
    |
+LL |         (1, 4 | 5) => {}
+   |         ^^^^^^^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:29:9
+   |
 LL |         (1 | 2, 3 | 4) => {}
    |         -------------- matches some of the same values
 ...
 LL |         (1, 5 | 6) => {}
    |         ---------- matches some of the same values
 LL |         (1, 4 | 5) => {}
-   |         ^^^^^^^^^^ unreachable pattern
+   |         ^^^^^^^^^^ collectively making this unreachable
 
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:34:13
@@ -177,10 +189,16 @@ LL |         (true, 0 | 0) => {}
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:84:17
    |
+LL |         (_, 0 | 0) => {}
+   |                 ^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:84:17
+   |
 LL |         (true, 0 | 0) => {}
    |                - matches some of the same values
 LL |         (_, 0 | 0) => {}
-   |             -   ^ unreachable pattern
+   |             -   ^ collectively making this unreachable
    |             |
    |             matches some of the same values
 
@@ -203,26 +221,40 @@ LL |         [true
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:111:36
    |
+LL |         (true | false, None | Some(true
+   |                                    ^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:111:36
+   |
 LL |         (true, Some(_)) => {}
    |                     - matches some of the same values
 LL |         (false, Some(true)) => {}
    |                      ---- matches some of the same values
 LL |         (true | false, None | Some(true
-   |                                    ^^^^ unreachable pattern
+   |                                    ^^^^ collectively making this unreachable
 
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:116:14
    |
 LL |             (true
    |              ^^^^ unreachable pattern
 ...
+LL |         (true | false, None | Some(t_or_f!())) => {}
+   |                                    --------- in this macro invocation
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:116:14
+   |
+LL |             (true
+   |              ^^^^ collectively making this unreachable
+...
 LL |         (true, Some(_)) => {}
    |                     - matches some of the same values
 LL |         (false, Some(true)) => {}
    |                      ---- matches some of the same values
 LL |         (true | false, None | Some(t_or_f!())) => {}
    |                                    --------- in this macro invocation
-   |
    = note: this error originates in the macro `t_or_f` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: unreachable pattern
@@ -245,24 +277,36 @@ LL |                 | false) => {}
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:154:15
    |
+LL |             | true) => {}
+   |               ^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:154:15
+   |
 LL |         (false, true) => {}
    |                 ---- matches some of the same values
 LL |         (true, true) => {}
    |                ---- matches some of the same values
 LL |         (false | true, false
 LL |             | true) => {}
-   |               ^^^^ unreachable pattern
+   |               ^^^^ collectively making this unreachable
 
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:160:15
    |
+LL |             | true,
+   |               ^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:160:15
+   |
 LL |         (true, false) => {}
    |          ---- matches some of the same values
 LL |         (true, true) => {}
    |          ---- matches some of the same values
 LL |         (false
 LL |             | true,
-   |               ^^^^ unreachable pattern
+   |               ^^^^ collectively making this unreachable
 
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:165:15

tests/ui/pattern/usefulness/consts-opaque.stderr

@@ -122,12 +122,18 @@ LL |         BAZ => {}
 error: unreachable pattern
   --> $DIR/consts-opaque.rs:87:9
    |
+LL |         _ => {} // should not be emitting unreachable warning
+   |         ^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/consts-opaque.rs:87:9
+   |
 LL |         BAZ => {}
    |         --- matches some of the same values
 LL |         Baz::Baz2 => {}
    |         --------- matches some of the same values
 LL |         _ => {} // should not be emitting unreachable warning
-   |         ^ unreachable pattern
+   |         ^ collectively making this unreachable
 
 error: aborting due to 17 previous errors
 

tests/ui/pattern/usefulness/explain-unreachable-pats.rs

@@ -22,6 +22,8 @@ fn main() {
         (1 | 2,) => {}
         //~^ ERROR unreachable pattern
         //~| NOTE unreachable pattern
+        //~| NOTE these patterns collectively make the last one unreachable
+        //~| NOTE collectively making this unreachable
         _ => {}
     }
 
@@ -69,6 +71,8 @@ fn main() {
         (_, true) => {}
         //~^ ERROR unreachable pattern
         //~| NOTE unreachable pattern
+        //~| NOTE these patterns collectively make the last one unreachable
+        //~| NOTE collectively making this unreachable
     }
 
     match (true, true) {

tests/ui/pattern/usefulness/explain-unreachable-pats.stderr

@@ -16,41 +16,47 @@ LL | #![deny(unreachable_patterns)]
 error: unreachable pattern
   --> $DIR/explain-unreachable-pats.rs:22:9
    |
+LL |         (1 | 2,) => {}
+   |         ^^^^^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/explain-unreachable-pats.rs:22:9
+   |
 LL |         (1,) => {}
    |         ---- matches some of the same values
 LL |
 LL |         (2,) => {}
    |         ---- matches some of the same values
 LL |
 LL |         (1 | 2,) => {}
-   |         ^^^^^^^^ unreachable pattern
+   |         ^^^^^^^^ collectively making this unreachable
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:31:9
+  --> $DIR/explain-unreachable-pats.rs:33:9
    |
 LL |         Err(_) => {}
    |         ^^^^^^
    |
    = note: this pattern matches no values because `!` is uninhabited
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:44:9
+  --> $DIR/explain-unreachable-pats.rs:46:9
    |
 LL |         (Err(_), Err(_)) => {}
    |         ^^^^^^^^^^^^^^^^
    |
    = note: this pattern matches no values because `Void2` is uninhabited
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:50:9
+  --> $DIR/explain-unreachable-pats.rs:52:9
    |
 LL |         (Err(_), Err(_)) => {}
    |         ^^^^^^^^^^^^^^^^
    |
    = note: this pattern matches no values because `Void1` is uninhabited
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:59:11
+  --> $DIR/explain-unreachable-pats.rs:61:11
    |
 LL |     if let (0
    |             - matches all the values already
@@ -59,7 +65,13 @@ LL |         | 0, _) = (0, 0) {}
    |           ^ unreachable pattern
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:69:9
+  --> $DIR/explain-unreachable-pats.rs:71:9
+   |
+LL |         (_, true) => {}
+   |         ^^^^^^^^^ unreachable pattern
+   |
+note: these patterns collectively make the last one unreachable
+  --> $DIR/explain-unreachable-pats.rs:71:9
    |
 LL |         (true, _) => {}
    |         --------- matches some of the same values
@@ -68,10 +80,10 @@ LL |         (false, _) => {}
    |         ---------- matches some of the same values
 LL |
 LL |         (_, true) => {}
-   |         ^^^^^^^^^ unreachable pattern
+   |         ^^^^^^^^^ collectively making this unreachable
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:80:9
+  --> $DIR/explain-unreachable-pats.rs:84:9
    |
 LL |         (true, _) => {}
    |         --------- matches all the values already
@@ -80,7 +92,7 @@ LL |         (true, true) => {}
    |         ^^^^^^^^^^^^ unreachable pattern
 
 error: unreachable pattern
-  --> $DIR/explain-unreachable-pats.rs:92:9
+  --> $DIR/explain-unreachable-pats.rs:96:9
    |
 LL |         (_, true, 0..10) => {}
    |         ---------------- matches all the values already