Make -Z treat-err-as-bug take a number of errors to be emitted

`-Z treat-err-as-bug=0` will cause `rustc` to panic after the first
error is reported. `-Z treat-err-as-bug=2` will cause `rustc` to
panic after 3 errors have been reported.

src/librustc/session/config.rs

@@ -1234,7 +1234,7 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "parse only; do not compile, assemble, or link"),
     no_codegen: bool = (false, parse_bool, [TRACKED],
         "run all passes except codegen; no output"),
-    treat_err_as_bug: bool = (false, parse_bool, [TRACKED],
+    treat_err_as_bug: Option<usize> = (None, parse_opt_uint, [TRACKED],
         "treat all errors that occur as bugs"),
     report_delayed_bugs: bool = (false, parse_bool, [TRACKED],
         "immediately print bugs registered with `delay_span_bug`"),
@@ -3212,7 +3212,7 @@ mod tests {
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
         opts = reference.clone();
-        opts.debugging_opts.treat_err_as_bug = true;
+        opts.debugging_opts.treat_err_as_bug = Some(1);
         assert!(reference.dep_tracking_hash() != opts.dep_tracking_hash());
 
         opts = reference.clone();

src/librustc/session/mod.rs

@@ -1315,7 +1315,7 @@ pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
             Box::new(EmitterWriter::stderr(color_config, None, true, false))
         }
     };
-    let handler = errors::Handler::with_emitter(true, false, emitter);
+    let handler = errors::Handler::with_emitter(true, None, emitter);
     handler.emit(&MultiSpan::new(), msg, errors::Level::Fatal);
     errors::FatalError.raise();
 }
@@ -1330,7 +1330,7 @@ pub fn early_warn(output: config::ErrorOutputType, msg: &str) {
             Box::new(EmitterWriter::stderr(color_config, None, true, false))
         }
     };
-    let handler = errors::Handler::with_emitter(true, false, emitter);
+    let handler = errors::Handler::with_emitter(true, None, emitter);
     handler.emit(&MultiSpan::new(), msg, errors::Level::Warning);
 }
 

src/librustc_codegen_ssa/back/write.rs

@@ -247,7 +247,7 @@ pub struct CodegenContext<B: WriteBackendMethods> {
 
 impl<B: WriteBackendMethods> CodegenContext<B> {
     pub fn create_diag_handler(&self) -> Handler {
-        Handler::with_emitter(true, false, Box::new(self.diag_emitter.clone()))
+        Handler::with_emitter(true, None, Box::new(self.diag_emitter.clone()))
     }
 
     pub fn config(&self, kind: ModuleKind) -> &ModuleConfig {

src/librustc_driver/lib.rs

@@ -148,7 +148,7 @@ pub fn run<F>(run_compiler: F) -> isize
                                 true,
                                 false
                             );
-                        let handler = errors::Handler::with_emitter(true, false, Box::new(emitter));
+                        let handler = errors::Handler::with_emitter(true, None, Box::new(emitter));
                         handler.emit(&MultiSpan::new(),
                                      "aborting due to previous error(s)",
                                      errors::Level::Fatal);
@@ -1327,7 +1327,7 @@ pub fn monitor<F: FnOnce() + Send + 'static>(f: F) -> Result<(), CompilationFail
                                                                 None,
                                                                 false,
                                                                 false));
-            let handler = errors::Handler::with_emitter(true, false, emitter);
+            let handler = errors::Handler::with_emitter(true, None, emitter);
 
             // a .span_bug or .bug call has already printed what
             // it wants to print.

src/librustc_errors/diagnostic_builder.rs

@@ -103,7 +103,7 @@ impl<'a> DiagnosticBuilder<'a> {
     /// Buffers the diagnostic for later emission, unless handler
     /// has disabled such buffering.
     pub fn buffer(mut self, buffered_diagnostics: &mut Vec<Diagnostic>) {
-        if self.handler.flags.dont_buffer_diagnostics || self.handler.flags.treat_err_as_bug {
+        if self.handler.flags.dont_buffer_diagnostics || self.handler.treat_err_as_bug() {
             self.emit();
             return;
         }

src/librustc_errors/lib.rs

@@ -330,7 +330,7 @@ pub struct HandlerFlags {
     pub can_emit_warnings: bool,
     /// If true, error-level diagnostics are upgraded to bug-level.
     /// (rustc: see `-Z treat-err-as-bug`)
-    pub treat_err_as_bug: bool,
+    pub treat_err_as_bug: Option<usize>,
     /// If true, immediately emit diagnostics that would otherwise be buffered.
     /// (rustc: see `-Z dont-buffer-diagnostics` and `-Z treat-err-as-bug`)
     pub dont_buffer_diagnostics: bool,
@@ -360,7 +360,7 @@ impl Drop for Handler {
 impl Handler {
     pub fn with_tty_emitter(color_config: ColorConfig,
                             can_emit_warnings: bool,
-                            treat_err_as_bug: bool,
+                            treat_err_as_bug: Option<usize>,
                             cm: Option<Lrc<SourceMapperDyn>>)
                             -> Handler {
         Handler::with_tty_emitter_and_flags(
@@ -382,7 +382,7 @@ impl Handler {
     }
 
     pub fn with_emitter(can_emit_warnings: bool,
-                        treat_err_as_bug: bool,
+                        treat_err_as_bug: Option<usize>,
                         e: Box<dyn Emitter + sync::Send>)
                         -> Handler {
         Handler::with_emitter_and_flags(
@@ -516,7 +516,7 @@ impl Handler {
     }
 
     fn panic_if_treat_err_as_bug(&self) {
-        if self.flags.treat_err_as_bug {
+        if self.treat_err_as_bug() {
             panic!("encountered error with `-Z treat_err_as_bug");
         }
     }
@@ -558,7 +558,7 @@ impl Handler {
         panic!(ExplicitBug);
     }
     pub fn delay_span_bug<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
-        if self.flags.treat_err_as_bug {
+        if self.treat_err_as_bug() {
             // FIXME: don't abort here if report_delayed_bugs is off
             self.span_bug(sp, msg);
         }
@@ -593,14 +593,14 @@ impl Handler {
         DiagnosticBuilder::new(self, FailureNote, msg).emit()
     }
     pub fn fatal(&self, msg: &str) -> FatalError {
-        if self.flags.treat_err_as_bug {
+        if self.treat_err_as_bug() {
             self.bug(msg);
         }
         DiagnosticBuilder::new(self, Fatal, msg).emit();
         FatalError
     }
     pub fn err(&self, msg: &str) {
-        if self.flags.treat_err_as_bug {
+        if self.treat_err_as_bug() {
             self.bug(msg);
         }
         let mut db = DiagnosticBuilder::new(self, Error, msg);
@@ -610,6 +610,9 @@ impl Handler {
         let mut db = DiagnosticBuilder::new(self, Warning, msg);
         db.emit();
     }
+    fn treat_err_as_bug(&self) -> bool {
+        self.flags.treat_err_as_bug.map(|c| self.err_count() >= c).unwrap_or(false)
+    }
     pub fn note_without_error(&self, msg: &str) {
         let mut db = DiagnosticBuilder::new(self, Note, msg);
         db.emit();
@@ -624,8 +627,8 @@ impl Handler {
     }
 
     fn bump_err_count(&self) {
-        self.panic_if_treat_err_as_bug();
         self.err_count.fetch_add(1, SeqCst);
+        self.panic_if_treat_err_as_bug();
     }
 
     pub fn err_count(&self) -> usize {
@@ -643,7 +646,13 @@ impl Handler {
             _ => format!("aborting due to {} previous errors", self.err_count())
         };
 
-        let _ = self.fatal(&s);
+        let _ = if self.treat_err_as_bug() {
+            self.fatal(&s)
+        } else {
+            // only emit one backtrace when using `-Z treat-err-as-bug=X`
+            DiagnosticBuilder::new(self, Fatal, &s).emit();
+            FatalError
+        };
 
         let can_show_explain = self.emitter.borrow().should_show_explain();
         let are_there_diagnostics = !self.emitted_diagnostic_codes.borrow().is_empty();

src/librustdoc/core.rs

@@ -266,7 +266,7 @@ impl DocAccessLevels for AccessLevels<DefId> {
 /// will be created for the handler.
 pub fn new_handler(error_format: ErrorOutputType,
                    source_map: Option<Lrc<source_map::SourceMap>>,
-                   treat_err_as_bug: bool,
+                   treat_err_as_bug: Option<usize>,
                    ui_testing: bool,
 ) -> errors::Handler {
     // rustdoc doesn't override (or allow to override) anything from this that is relevant here, so

src/libsyntax/parse/mod.rs

@@ -53,7 +53,7 @@ impl ParseSess {
         let cm = Lrc::new(SourceMap::new(file_path_mapping));
         let handler = Handler::with_tty_emitter(ColorConfig::Auto,
                                                 true,
-                                                false,
+                                                None,
                                                 Some(cm.clone()));
         ParseSess::with_span_handler(handler, cm)
     }