conditionally ignore fatal diagnostic in the SilentEmitter

compiler/rustc_errors/src/emitter.rs

@@ -541,6 +541,7 @@ pub struct SilentEmitter {
     pub fallback_bundle: LazyFallbackBundle,
     pub fatal_dcx: DiagCtxt,
     pub fatal_note: Option<String>,
+    pub emit_fatal_diagnostic: bool,
 }
 
 impl Translate for SilentEmitter {
@@ -561,7 +562,7 @@ impl Emitter for SilentEmitter {
     }
 
     fn emit_diagnostic(&mut self, mut diag: DiagInner) {
-        if diag.level == Level::Fatal {
+        if self.emit_fatal_diagnostic && diag.level == Level::Fatal {
             if let Some(fatal_note) = &self.fatal_note {
                 diag.sub(Level::Note, fatal_note.clone(), MultiSpan::new());
             }

compiler/rustc_errors/src/lib.rs

@@ -613,12 +613,18 @@ impl DiagCtxt {
         Self { inner: Lock::new(DiagCtxtInner::new(emitter)) }
     }
 
-    pub fn make_silent(&mut self, fallback_bundle: LazyFallbackBundle, fatal_note: Option<String>) {
+    pub fn make_silent(
+        &mut self,
+        fallback_bundle: LazyFallbackBundle,
+        fatal_note: Option<String>,
+        emit_fatal_diagnostic: bool,
+    ) {
         self.wrap_emitter(|old_dcx| {
             Box::new(emitter::SilentEmitter {
                 fallback_bundle,
                 fatal_dcx: DiagCtxt { inner: Lock::new(old_dcx) },
                 fatal_note,
+                emit_fatal_diagnostic,
             })
         });
     }

compiler/rustc_interface/src/interface.rs

@@ -48,6 +48,7 @@ pub(crate) fn parse_cfg(dcx: &DiagCtxt, cfgs: Vec<String>) -> Cfg {
             let psess = ParseSess::with_silent_emitter(
                 vec![crate::DEFAULT_LOCALE_RESOURCE, rustc_parse::DEFAULT_LOCALE_RESOURCE],
                 format!("this error occurred on the command line: `--cfg={s}`"),
+                true,
             );
             let filename = FileName::cfg_spec_source_code(&s);
 
@@ -111,6 +112,7 @@ pub(crate) fn parse_check_cfg(dcx: &DiagCtxt, specs: Vec<String>) -> CheckCfg {
         let psess = ParseSess::with_silent_emitter(
             vec![crate::DEFAULT_LOCALE_RESOURCE, rustc_parse::DEFAULT_LOCALE_RESOURCE],
             format!("this error occurred on the command line: `--check-cfg={s}`"),
+            true,
         );
         let filename = FileName::cfg_spec_source_code(&s);
 

compiler/rustc_session/src/parse.rs

@@ -269,7 +269,11 @@ impl ParseSess {
         }
     }
 
-    pub fn with_silent_emitter(locale_resources: Vec<&'static str>, fatal_note: String) -> Self {
+    pub fn with_silent_emitter(
+        locale_resources: Vec<&'static str>,
+        fatal_note: String,
+        emit_fatal_diagnostic: bool,
+    ) -> Self {
         let fallback_bundle = fallback_fluent_bundle(locale_resources, false);
         let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
         let emitter = Box::new(HumanEmitter::new(
@@ -281,6 +285,7 @@ impl ParseSess {
             fallback_bundle,
             fatal_dcx,
             fatal_note: Some(fatal_note),
+            emit_fatal_diagnostic,
         }))
         .disable_warnings();
         ParseSess::with_dcx(dcx, sm)

src/tools/rustfmt/src/parse/session.rs

@@ -121,6 +121,7 @@ fn default_dcx(
             fallback_bundle,
             fatal_dcx: DiagCtxt::new(emitter),
             fatal_note: None,
+            emit_fatal_diagnostic: false,
         })
     } else {
         emitter
@@ -209,7 +210,7 @@ impl ParseSess {
             rustc_driver::DEFAULT_LOCALE_RESOURCES.to_vec(),
             false,
         );
-        self.raw_psess.dcx.make_silent(fallback_bundle, None);
+        self.raw_psess.dcx.make_silent(fallback_bundle, None, false);
     }
 
     pub(crate) fn span_to_filename(&self, span: Span) -> FileName {