Remove force_print_diagnostic.

There are a couple of places where we call
`inner.emitter.emit_diagnostic` directly rather than going through
`inner.emit_diagnostic`, to guarantee the diagnostic is printed. This
feels dubious to me, particularly the bypassing of `TRACK_DIAGNOSTIC`.

This commit removes those.
- In `print_error_count`, it uses `ForceWarning` instead of `Warning`.
- It removes `DiagCtxtInner::failure_note`, because it only has three
  uses and direct use of `emit_diagnostic` is consistent with other
  similar locations.
- It removes `force_print_diagnostic`, and adds `struct_failure_note`,
  and updates `print_query_stack` accordingly, which makes it more
  normal. That location doesn't seem to need forced printing anyway.

compiler/rustc_errors/src/lib.rs

@@ -780,11 +780,12 @@ impl DiagCtxt {
         match (errors.len(), warnings.len()) {
             (0, 0) => return,
             (0, _) => {
-                // Use `inner.emitter` directly, otherwise the warning might not be emitted, e.g.
-                // with a configuration like `--cap-lints allow --force-warn bare_trait_objects`.
-                inner
-                    .emitter
-                    .emit_diagnostic(Diagnostic::new(Warning, DiagnosticMessage::Str(warnings)));
+                // Use `ForceWarning` rather than `Warning` to guarantee emission, e.g. with a
+                // configuration like `--cap-lints allow --force-warn bare_trait_objects`.
+                inner.emit_diagnostic(Diagnostic::new(
+                    ForceWarning(None),
+                    DiagnosticMessage::Str(warnings),
+                ));
             }
             (_, 0) => {
                 inner.emit_diagnostic(Diagnostic::new(Error, errors));
@@ -812,20 +813,23 @@ impl DiagCtxt {
                 error_codes.sort();
                 if error_codes.len() > 1 {
                     let limit = if error_codes.len() > 9 { 9 } else { error_codes.len() };
-                    inner.failure_note(format!(
+                    let msg1 = format!(
                         "Some errors have detailed explanations: {}{}",
                         error_codes[..limit].join(", "),
                         if error_codes.len() > 9 { "..." } else { "." }
-                    ));
-                    inner.failure_note(format!(
+                    );
+                    let msg2 = format!(
                         "For more information about an error, try `rustc --explain {}`.",
                         &error_codes[0]
-                    ));
+                    );
+                    inner.emit_diagnostic(Diagnostic::new(FailureNote, msg1));
+                    inner.emit_diagnostic(Diagnostic::new(FailureNote, msg2));
                 } else {
-                    inner.failure_note(format!(
+                    let msg = format!(
                         "For more information about this error, try `rustc --explain {}`.",
                         &error_codes[0]
-                    ));
+                    );
+                    inner.emit_diagnostic(Diagnostic::new(FailureNote, msg));
                 }
             }
         }
@@ -848,10 +852,6 @@ impl DiagCtxt {
         self.inner.borrow_mut().taught_diagnostics.insert(code)
     }
 
-    pub fn force_print_diagnostic(&self, db: Diagnostic) {
-        self.inner.borrow_mut().emitter.emit_diagnostic(db);
-    }
-
     pub fn emit_diagnostic(&self, diagnostic: Diagnostic) -> Option<ErrorGuaranteed> {
         self.inner.borrow_mut().emit_diagnostic(diagnostic)
     }
@@ -1207,6 +1207,15 @@ impl DiagCtxt {
         DiagnosticBuilder::new(self, Help, msg)
     }
 
+    #[rustc_lint_diagnostics]
+    #[track_caller]
+    pub fn struct_failure_note(
+        &self,
+        msg: impl Into<DiagnosticMessage>,
+    ) -> DiagnosticBuilder<'_, ()> {
+        DiagnosticBuilder::new(self, FailureNote, msg)
+    }
+
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn struct_allow(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_, ()> {
@@ -1406,10 +1415,6 @@ impl DiagCtxtInner {
             .or_else(|| self.delayed_bugs.get(0).map(|(_, guar)| guar).copied())
     }
 
-    fn failure_note(&mut self, msg: impl Into<DiagnosticMessage>) {
-        self.emit_diagnostic(Diagnostic::new(FailureNote, msg));
-    }
-
     fn flush_delayed(&mut self) {
         if self.delayed_bugs.is_empty() {
             return;

compiler/rustc_query_system/src/query/job.rs

@@ -4,7 +4,7 @@ use crate::query::plumbing::CycleError;
 use crate::query::DepKind;
 use crate::query::{QueryContext, QueryStackFrame};
 use rustc_data_structures::fx::FxHashMap;
-use rustc_errors::{DiagCtxt, Diagnostic, DiagnosticBuilder, Level};
+use rustc_errors::{DiagCtxt, DiagnosticBuilder};
 use rustc_hir::def::DefKind;
 use rustc_session::Session;
 use rustc_span::Span;
@@ -628,15 +628,15 @@ pub fn print_query_stack<Qcx: QueryContext>(
         };
         if Some(count_printed) < num_frames || num_frames.is_none() {
             // Only print to stderr as many stack frames as `num_frames` when present.
-            let mut diag = Diagnostic::new(
-                Level::FailureNote,
-                format!(
+            // FIXME: needs translation
+            #[allow(rustc::diagnostic_outside_of_impl)]
+            #[allow(rustc::untranslatable_diagnostic)]
+            dcx.struct_failure_note(format!(
                 "#{} [{:?}] {}",
                 count_printed, query_info.query.dep_kind, query_info.query.description
-                ),
-            );
-            diag.span = query_info.job.span.into();
-            dcx.force_print_diagnostic(diag);
+            ))
+            .with_span(query_info.job.span)
+            .emit();
             count_printed += 1;
         }