Give TRACK_DIAGNOSTIC a return value.

This means `DiagCtxtInner::emit_diagnostic` can return its result
directly, rather than having to modify a local variable.

compiler/rustc_errors/src/lib.rs

@@ -516,12 +516,16 @@ pub enum StashKey {
     UndeterminedMacroResolution,
 }
 
-fn default_track_diagnostic(diag: Diagnostic, f: &mut dyn FnMut(Diagnostic)) {
+fn default_track_diagnostic<R>(diag: Diagnostic, f: &mut dyn FnMut(Diagnostic) -> R) -> R {
     (*f)(diag)
 }
 
-pub static TRACK_DIAGNOSTIC: AtomicRef<fn(Diagnostic, &mut dyn FnMut(Diagnostic))> =
-    AtomicRef::new(&(default_track_diagnostic as _));
+pub static TRACK_DIAGNOSTIC: AtomicRef<
+    fn(
+        Diagnostic,
+        &mut dyn FnMut(Diagnostic) -> Option<ErrorGuaranteed>,
+    ) -> Option<ErrorGuaranteed>,
+> = AtomicRef::new(&(default_track_diagnostic as _));
 
 enum DelayedBugKind {
     Normal,
@@ -1303,7 +1307,6 @@ impl DiagCtxtInner {
             _ => {}
         }
 
-        let mut guaranteed = None;
         TRACK_DIAGNOSTIC(diagnostic, &mut |mut diagnostic| {
             if let Some(code) = diagnostic.code {
                 self.emitted_diagnostic_codes.insert(code);
@@ -1365,11 +1368,11 @@ impl DiagCtxtInner {
 
             #[allow(deprecated)]
             if level == Level::Error {
-                guaranteed = Some(ErrorGuaranteed::unchecked_error_guaranteed());
+                Some(ErrorGuaranteed::unchecked_error_guaranteed())
+            } else {
+                None
             }
-        });
-
-        guaranteed
+        })
     }
 
     fn treat_err_as_bug(&self) -> bool {

compiler/rustc_interface/src/callbacks.rs

@@ -29,7 +29,7 @@ fn track_span_parent(def_id: rustc_span::def_id::LocalDefId) {
 /// This is a callback from `rustc_errors` as it cannot access the implicit state
 /// in `rustc_middle` otherwise. It is used when diagnostic messages are
 /// emitted and stores them in the current query, if there is one.
-fn track_diagnostic(diagnostic: Diagnostic, f: &mut dyn FnMut(Diagnostic)) {
+fn track_diagnostic<R>(diagnostic: Diagnostic, f: &mut dyn FnMut(Diagnostic) -> R) -> R {
     tls::with_context_opt(|icx| {
         if let Some(icx) = icx {
             if let Some(diagnostics) = icx.diagnostics {
@@ -38,11 +38,11 @@ fn track_diagnostic(diagnostic: Diagnostic, f: &mut dyn FnMut(Diagnostic)) {
 
             // Diagnostics are tracked, we can ignore the dependency.
             let icx = tls::ImplicitCtxt { task_deps: TaskDepsRef::Ignore, ..icx.clone() };
-            return tls::enter_context(&icx, move || (*f)(diagnostic));
+            tls::enter_context(&icx, move || (*f)(diagnostic))
+        } else {
+            // In any other case, invoke diagnostics anyway.
+            (*f)(diagnostic)
         }
-
-        // In any other case, invoke diagnostics anyway.
-        (*f)(diagnostic);
     })
 }