Fix ICE if original_span(fn_sig) returns a span not in body sourcefile

Fixes: #84421

2 files changed, 4 insertions, 8 deletions

diff --git a/compiler/rustc_mir/src/transform/coverage/mod.rs b/compiler/rustc_mir/src/transform/coverage/mod.rs
index 93133e9b7f0..60757178bec 100644
--- a/compiler/rustc_mir/src/transform/coverage/mod.rs
+++ b/compiler/rustc_mir/src/transform/coverage/mod.rs
@@ -111,7 +111,8 @@ impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
         let body_span = hir_body.value.span;
         let source_file = source_map.lookup_source_file(body_span.lo());
         let fn_sig_span = match some_fn_sig.filter(|fn_sig| {
-            Lrc::ptr_eq(&source_file, &source_map.lookup_source_file(fn_sig.span.hi()))
+            fn_sig.span.ctxt() == body_span.ctxt()
+                && Lrc::ptr_eq(&source_file, &source_map.lookup_source_file(fn_sig.span.hi()))
         }) {
             Some(fn_sig) => fn_sig.span.with_hi(body_span.lo()),
             None => body_span.shrink_to_lo(),
diff --git a/compiler/rustc_mir/src/transform/coverage/spans.rs b/compiler/rustc_mir/src/transform/coverage/spans.rs
index 067e1001def..249f5e835cd 100644
--- a/compiler/rustc_mir/src/transform/coverage/spans.rs
+++ b/compiler/rustc_mir/src/transform/coverage/spans.rs
@@ -240,13 +240,13 @@ impl<'a, 'tcx> CoverageSpans<'a, 'tcx> {
     /// to be).
     pub(super) fn generate_coverage_spans(
         mir_body: &'a mir::Body<'tcx>,
-        fn_sig_span: Span,
+        fn_sig_span: Span, // Ensured to be same SourceFile and SyntaxContext as `body_span`
         body_span: Span,
         basic_coverage_blocks: &'a CoverageGraph,
     ) -> Vec<CoverageSpan> {
         let mut coverage_spans = CoverageSpans {
             mir_body,
-            fn_sig_span: fn_sig_source_span(fn_sig_span, body_span),
+            fn_sig_span,
             body_span,
             basic_coverage_blocks,
             sorted_spans_iter: None,
@@ -732,11 +732,6 @@ pub(super) fn filtered_terminator_span(
 }
 
 #[inline]
-fn fn_sig_source_span(fn_sig_span: Span, body_span: Span) -> Span {
-    original_sp(fn_sig_span, body_span).with_ctxt(body_span.ctxt())
-}
-
-#[inline]
 fn function_source_span(span: Span, body_span: Span) -> Span {
     let span = original_sp(span, body_span).with_ctxt(body_span.ctxt());
     if body_span.contains(span) { span } else { body_span }