Translate Overlap eagerly

Author: mejrs

compiler/rustc_error_messages/locales/en-US/mir_build.ftl

@@ -323,8 +323,6 @@ mir_build_overlapping_range_endpoints = multiple patterns overlap on their endpo
     .range = ... with this range
     .note = you likely meant to write mutually exclusive ranges
 
-mir_build_overlapping_range = this range overlaps on `{$range}`...
-
 mir_build_non_exhaustive_omitted_pattern = some variants are not matched explicitly
     .help = ensure that all variants are matched explicitly by adding the suggested match arms
     .note = the matched value is of type `{$scrut_ty}` and the `non_exhaustive_omitted_patterns` attribute was found

compiler/rustc_mir_build/src/errors.rs

@@ -677,17 +677,28 @@ pub struct OverlappingRangeEndpoints<'tcx> {
     #[label(range)]
     pub range: Span,
     #[subdiagnostic]
-    pub overlap: Overlap<'tcx>,
+    pub overlap: Vec<Overlap<'tcx>>,
 }
 
-#[derive(Subdiagnostic)]
-#[label(mir_build_overlapping_range)]
 pub struct Overlap<'tcx> {
-    #[primary_span]
     pub span: Span,
     pub range: Pat<'tcx>,
 }
 
+impl<'tcx> AddToDiagnostic for Overlap<'tcx> {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
+        let Overlap { span, range } = self;
+
+        // FIXME(mejrs) unfortunately `#[derive(LintDiagnostic)]`
+        // does not support `#[subdiagnostic(eager)]`...
+        let message = format!("this range overlaps on `{range}`...");
+        diag.span_label(span, message);
+    }
+}
+
 #[derive(LintDiagnostic)]
 #[diag(mir_build_non_exhaustive_omitted_pattern)]
 #[help]

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

@@ -285,19 +285,16 @@ impl IntRange {
             return;
         }
 
-        // Get the first overlap. We get only the first rather than all of them
-        // because displaying multiple overlaps requires a way to eagerly translate
-        // lintdiagnostics, but that doesn't exist.
-        let overlap = pats
+        let overlap: Vec<_> = pats
             .filter_map(|pat| Some((pat.ctor().as_int_range()?, pat.span())))
             .filter(|(range, _)| self.suspicious_intersection(range))
             .map(|(range, span)| Overlap {
                 range: self.intersection(&range).unwrap().to_pat(pcx.cx.tcx, pcx.ty),
                 span,
             })
-            .next();
+            .collect();
 
-        if let Some(overlap) = overlap {
+        if !overlap.is_empty() {
             pcx.cx.tcx.emit_spanned_lint(
                 lint::builtin::OVERLAPPING_RANGE_ENDPOINTS,
                 hir_id,

tests/ui/pattern/usefulness/integer-ranges/overlapping_range_endpoints.stderr

@@ -59,6 +59,7 @@ error: multiple patterns overlap on their endpoints
 LL |         0..=10 => {}
    |         ------ this range overlaps on `10_u8`...
 LL |         20..=30 => {}
+   |         ------- this range overlaps on `20_u8`...
 LL |         10..=20 => {}
    |         ^^^^^^^ ... with this range
    |