Tweak unreachable lint wording

compiler/rustc_mir_build/messages.ftl

@@ -327,14 +327,17 @@ mir_build_union_pattern = cannot use unions in constant patterns
 
 mir_build_unreachable_making_this_unreachable = collectively making this unreachable
 
+mir_build_unreachable_making_this_unreachable_n_more = ...and {$covered_by_many_n_more_count} other patterns collectively make 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 `{$ty}` is uninhabited
+ .label = no value can reach this
+ .unreachable_matches_no_values = matches no values because `{$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 values already
- .unreachable_covered_by_many = these patterns collectively make the last one unreachable
+ .unreachable_covered_by_one = matches all the relevant values
+ .unreachable_covered_by_many = multiple earlier patterns match some of the same values
 
 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

@@ -588,12 +588,15 @@ pub(crate) struct UnreachablePattern<'tcx> {
  pub(crate) span: Option<Span>,
  #[subdiagnostic]
  pub(crate) matches_no_values: Option<UnreachableMatchesNoValues<'tcx>>,
+ #[note(mir_build_unreachable_uninhabited_note)]
+ pub(crate) uninhabited_note: Option<()>,
  #[label(mir_build_unreachable_covered_by_catchall)]
  pub(crate) covered_by_catchall: Option<Span>,
  #[label(mir_build_unreachable_covered_by_one)]
  pub(crate) covered_by_one: Option<Span>,
  #[note(mir_build_unreachable_covered_by_many)]
  pub(crate) covered_by_many: Option<MultiSpan>,
+ pub(crate) covered_by_many_n_more_count: usize,
 }
 
 #[derive(Subdiagnostic)]

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

@@ -917,18 +917,22 @@ fn report_unreachable_pattern<'p, 'tcx>(
  pat: &DeconstructedPat<'p, 'tcx>,
  explanation: &RedundancyExplanation<'p, 'tcx>,
 ) {
+ static CAP_COVERED_BY_MANY: usize = 4;
  let pat_span = pat.data().span;
  let mut lint = UnreachablePattern {
  span: Some(pat_span),
  matches_no_values: None,
+ uninhabited_note: None,
  covered_by_catchall: None,
  covered_by_one: None,
  covered_by_many: None,
+ covered_by_many_n_more_count: 0,
  };
  match explanation.covered_by.as_slice() {
  [] => {
  // 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
  pat.walk(&mut |subpat| {
  let ty = **subpat.ty();
  if cx.is_uninhabited(ty) {
@@ -948,15 +952,27 @@ fn report_unreachable_pattern<'p, 'tcx>(
  lint.covered_by_one = Some(covering_pat.data().span);
  }
  covering_pats => {
+ let mut iter = covering_pats.iter();
  let mut multispan = MultiSpan::from_span(pat_span);
- for p in covering_pats {
+ for p in iter.by_ref().take(CAP_COVERED_BY_MANY) {
  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);
+ let remain = iter.count();
+ if remain == 0 {
+ multispan.push_span_label(
+ pat_span,
+ fluent::mir_build_unreachable_making_this_unreachable,
+ );
+ } else {
+ lint.covered_by_many_n_more_count = remain;
+ multispan.push_span_label(
+ pat_span,
+ fluent::mir_build_unreachable_making_this_unreachable_n_more,
+ );
+ }
  lint.covered_by_many = Some(multispan);
  }
  }

tests/ui/consts/packed_pattern.stderr

@@ -2,9 +2,9 @@ warning: unreachable pattern
  --> $DIR/packed_pattern.rs:16:9
  |
 LL | Foo { field: (5, 6, 7, 8) } => {},
- | --------------------------- matches all the values already
+ | --------------------------- matches all the relevant values
 LL | FOO => unreachable!(),
- | ^^^ unreachable pattern
+ | ^^^ no value can reach this
  |
  = note: `#[warn(unreachable_patterns)]` on by default
 

tests/ui/consts/packed_pattern2.stderr

@@ -2,9 +2,9 @@ warning: unreachable pattern
  --> $DIR/packed_pattern2.rs:24:9
  |
 LL | Bar { a: Foo { field: (5, 6) } } => {},
- | -------------------------------- matches all the values already
+ | -------------------------------- matches all the relevant values
 LL | FOO => unreachable!(),
- | ^^^ unreachable pattern
+ | ^^^ no value can reach this
  |
  = note: `#[warn(unreachable_patterns)]` on by default
 

tests/ui/error-codes/E0001.stderr

@@ -2,9 +2,9 @@ error: unreachable pattern
  --> $DIR/E0001.rs:8:9
  |
 LL | _ => {/* ... */}
- | ^ unreachable pattern
+ | ^ no value can reach this
  |
-note: these patterns collectively make the last one unreachable
+note: multiple earlier patterns match some of the same values
  --> $DIR/E0001.rs:8:9
  |
 LL | Some(_) => {/* ... */}

tests/ui/lint/issue-30302.stderr

@@ -13,7 +13,7 @@ LL | Nil => true,
  | --- matches any value
 LL |
 LL | _ => false
- | ^ unreachable pattern
+ | ^ no value can reach this
  |
 note: the lint level is defined here
  --> $DIR/issue-30302.rs:4:9