Point at uncovered variants in enum definition in note instead of a span_label

This makes the order of the output always consistent:

1. Place of the `match` missing arms
2. The `enum` definition span
3. The structured suggestion to add a fallthrough arm

Author: estebank

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

@@ -17,7 +17,7 @@ use rustc_session::lint::builtin::{
     BINDINGS_WITH_VARIANT_NAME, IRREFUTABLE_LET_PATTERNS, UNREACHABLE_PATTERNS,
 };
 use rustc_session::Session;
-use rustc_span::{DesugaringKind, ExpnKind, Span};
+use rustc_span::{DesugaringKind, ExpnKind, MultiSpan, Span};
 
 crate fn check_match(tcx: TyCtxt<'_>, def_id: DefId) {
     let body_id = match def_id.as_local() {
@@ -671,15 +671,27 @@ fn adt_defined_here<'p, 'tcx>(
 ) {
     let ty = ty.peel_refs();
     if let ty::Adt(def, _) = ty.kind() {
-        if let Some(sp) = cx.tcx.hir().span_if_local(def.did) {
-            err.span_label(sp, format!("`{}` defined here", ty));
-        }
-
-        if witnesses.len() < 4 {
+        let mut spans = vec![];
+        if witnesses.len() < 5 {
             for sp in maybe_point_at_variant(cx, def, witnesses.iter()) {
-                err.span_label(sp, "not covered");
+                spans.push(sp);
             }
         }
+        let def_span = cx
+            .tcx
+            .hir()
+            .get_if_local(def.did)
+            .and_then(|node| node.ident())
+            .map(|ident| ident.span)
+            .unwrap_or_else(|| cx.tcx.def_span(def.did));
+        let mut span: MultiSpan =
+            if spans.is_empty() { def_span.into() } else { spans.clone().into() };
+
+        span.push_span_label(def_span, String::new());
+        for pat in spans {
+            span.push_span_label(pat, "not covered".to_string());
+        }
+        err.span_note(span, &format!("`{}` defined here", ty));
     }
 }
 

src/test/ui/closures/2229_closure_analysis/match/issue-88331.stderr

@@ -1,12 +1,14 @@
 error[E0004]: non-exhaustive patterns: `Opcode(0_u8)` and `Opcode(2_u8..=u8::MAX)` not covered
   --> $DIR/issue-88331.rs:11:20
    |
-LL | pub struct Opcode(pub u8);
-   | -------------------------- `Opcode` defined here
-...
 LL |     move |i| match msg_type {
    |                    ^^^^^^^^ patterns `Opcode(0_u8)` and `Opcode(2_u8..=u8::MAX)` not covered
    |
+note: `Opcode` defined here
+  --> $DIR/issue-88331.rs:4:12
+   |
+LL | pub struct Opcode(pub u8);
+   |            ^^^^^^
    = note: the matched value is of type `Opcode`
 help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
    |
@@ -17,12 +19,14 @@ LL ~         Opcode(0_u8) | Opcode(2_u8..=u8::MAX) => todo!(),
 error[E0004]: non-exhaustive patterns: `Opcode2(Opcode(0_u8))` and `Opcode2(Opcode(2_u8..=u8::MAX))` not covered
   --> $DIR/issue-88331.rs:27:20
    |
-LL | pub struct Opcode2(Opcode);
-   | --------------------------- `Opcode2` defined here
-...
 LL |     move |i| match msg_type {
    |                    ^^^^^^^^ patterns `Opcode2(Opcode(0_u8))` and `Opcode2(Opcode(2_u8..=u8::MAX))` not covered
    |
+note: `Opcode2` defined here
+  --> $DIR/issue-88331.rs:18:12
+   |
+LL | pub struct Opcode2(Opcode);
+   |            ^^^^^^^
    = note: the matched value is of type `Opcode2`
 help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
    |