Rollup merge of #103970 - oli-obk:unhide_unknown_spans, r=estebank

Unhide unknown spans

r? ```@estebank```

2 files changed, 40 insertions, 21 deletions

diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
index f14b8ee3254..c450c276366 100644
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@@ -52,7 +52,6 @@ impl Emitter for AnnotateSnippetEmitterWriter {
         let (mut primary_span, suggestions) = self.primary_span_formatted(&diag, &fluent_args);
 
         self.fix_multispans_in_extern_macros_and_render_macro_backtrace(
-            &self.source_map,
             &mut primary_span,
             &mut children,
             &diag.level,
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index b7b8fe3f25a..55c7997a513 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -314,7 +314,6 @@ pub trait Emitter: Translate {
 
     fn fix_multispans_in_extern_macros_and_render_macro_backtrace(
         &self,
-        source_map: &Option<Lrc<SourceMap>>,
         span: &mut MultiSpan,
         children: &mut Vec<SubDiagnostic>,
         level: &Level,
@@ -340,7 +339,7 @@ pub trait Emitter: Translate {
             .collect();
 
         if !backtrace {
-            self.fix_multispans_in_extern_macros(source_map, span, children);
+            self.fix_multispans_in_extern_macros(span, children);
         }
 
         self.render_multispans_macro_backtrace(span, children, backtrace);
@@ -480,15 +479,13 @@ pub trait Emitter: Translate {
     // this will change the span to point at the use site.
     fn fix_multispans_in_extern_macros(
         &self,
-        source_map: &Option<Lrc<SourceMap>>,
         span: &mut MultiSpan,
         children: &mut Vec<SubDiagnostic>,
     ) {
-        let Some(source_map) = source_map else { return };
         debug!("fix_multispans_in_extern_macros: before: span={:?} children={:?}", span, children);
-        self.fix_multispan_in_extern_macros(source_map, span);
+        self.fix_multispan_in_extern_macros(span);
         for child in children.iter_mut() {
-            self.fix_multispan_in_extern_macros(source_map, &mut child.span);
+            self.fix_multispan_in_extern_macros(&mut child.span);
         }
         debug!("fix_multispans_in_extern_macros: after: span={:?} children={:?}", span, children);
     }
@@ -496,7 +493,8 @@ pub trait Emitter: Translate {
     // This "fixes" MultiSpans that contain `Span`s pointing to locations inside of external macros.
     // Since these locations are often difficult to read,
     // we move these spans from the external macros to their corresponding use site.
-    fn fix_multispan_in_extern_macros(&self, source_map: &Lrc<SourceMap>, span: &mut MultiSpan) {
+    fn fix_multispan_in_extern_macros(&self, span: &mut MultiSpan) {
+        let Some(source_map) = self.source_map() else { return };
         // First, find all the spans in external macros and point instead at their use site.
         let replacements: Vec<(Span, Span)> = span
             .primary_spans()
@@ -544,7 +542,6 @@ impl Emitter for EmitterWriter {
         debug!("emit_diagnostic: suggestions={:?}", suggestions);
 
         self.fix_multispans_in_extern_macros_and_render_macro_backtrace(
-            &self.sm,
             &mut primary_span,
             &mut children,
             &diag.level,
@@ -2213,22 +2210,45 @@ impl FileWithAnnotatedLines {
 
         if let Some(ref sm) = emitter.source_map() {
             for span_label in msp.span_labels() {
+                let fixup_lo_hi = |span: Span| {
+                    let lo = sm.lookup_char_pos(span.lo());
+                    let mut hi = sm.lookup_char_pos(span.hi());
+
+                    // Watch out for "empty spans". If we get a span like 6..6, we
+                    // want to just display a `^` at 6, so convert that to
+                    // 6..7. This is degenerate input, but it's best to degrade
+                    // gracefully -- and the parser likes to supply a span like
+                    // that for EOF, in particular.
+
+                    if lo.col_display == hi.col_display && lo.line == hi.line {
+                        hi.col_display += 1;
+                    }
+                    (lo, hi)
+                };
+
                 if span_label.span.is_dummy() {
+                    if let Some(span) = msp.primary_span() {
+                        // if we don't know where to render the annotation, emit it as a note
+                        // on the primary span.
+
+                        let (lo, hi) = fixup_lo_hi(span);
+
+                        let ann = Annotation {
+                            start_col: lo.col_display,
+                            end_col: hi.col_display,
+                            is_primary: span_label.is_primary,
+                            label: span_label
+                                .label
+                                .as_ref()
+                                .map(|m| emitter.translate_message(m, args).to_string()),
+                            annotation_type: AnnotationType::Singleline,
+                        };
+                        add_annotation_to_file(&mut output, lo.file, lo.line, ann);
+                    }
                     continue;
                 }
 
-                let lo = sm.lookup_char_pos(span_label.span.lo());
-                let mut hi = sm.lookup_char_pos(span_label.span.hi());
-
-                // Watch out for "empty spans". If we get a span like 6..6, we
-                // want to just display a `^` at 6, so convert that to
-                // 6..7. This is degenerate input, but it's best to degrade
-                // gracefully -- and the parser likes to supply a span like
-                // that for EOF, in particular.
-
-                if lo.col_display == hi.col_display && lo.line == hi.line {
-                    hi.col_display += 1;
-                }
+                let (lo, hi) = fixup_lo_hi(span_label.span);
 
                 if lo.line != hi.line {
                     let ml = MultilineAnnotation {