Do not capture stderr in the compiler. Instead just panic silently for fatal errors

src/librustc/hir/lowering.rs

@@ -2837,8 +2837,8 @@ impl<'a> LoweringContext<'a> {
                     (&None, &Some(..), Closed) => "RangeToInclusive",
                     (&Some(..), &Some(..), Closed) => "RangeInclusive",
                     (_, &None, Closed) =>
-                        panic!(self.diagnostic().span_fatal(
-                            e.span, "inclusive range with no end")),
+                        self.diagnostic().span_fatal(
+                            e.span, "inclusive range with no end").raise(),
                 };
 
                 let fields =

src/librustc/session/config.rs

@@ -1333,16 +1333,16 @@ pub fn build_target_config(opts: &Options, sp: &Handler) -> Config {
             sp.struct_fatal(&format!("Error loading target specification: {}", e))
                 .help("Use `--print target-list` for a list of built-in targets")
                 .emit();
-            panic!(FatalError);
+            FatalError.raise();
         }
     };
 
     let (isize_ty, usize_ty) = match &target.target_pointer_width[..] {
         "16" => (ast::IntTy::I16, ast::UintTy::U16),
         "32" => (ast::IntTy::I32, ast::UintTy::U32),
         "64" => (ast::IntTy::I64, ast::UintTy::U64),
-        w    => panic!(sp.fatal(&format!("target specification was invalid: \
-                                          unrecognized target-pointer-width {}", w))),
+        w    => sp.fatal(&format!("target specification was invalid: \
+                                          unrecognized target-pointer-width {}", w)).raise(),
     };
 
     Config {

src/librustc/session/mod.rs

@@ -250,18 +250,18 @@ impl Session {
     }
 
     pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, msg: &str) -> ! {
-        panic!(self.diagnostic().span_fatal(sp, msg))
+        self.diagnostic().span_fatal(sp, msg).raise()
     }
     pub fn span_fatal_with_code<S: Into<MultiSpan>>(
         &self,
         sp: S,
         msg: &str,
         code: DiagnosticId,
     ) -> ! {
-        panic!(self.diagnostic().span_fatal_with_code(sp, msg, code))
+        self.diagnostic().span_fatal_with_code(sp, msg, code).raise()
     }
     pub fn fatal(&self, msg: &str) -> ! {
-        panic!(self.diagnostic().fatal(msg))
+        self.diagnostic().fatal(msg).raise()
     }
     pub fn span_err_or_warn<S: Into<MultiSpan>>(&self, is_warning: bool, sp: S, msg: &str) {
         if is_warning {
@@ -919,7 +919,7 @@ pub fn build_session_(sopts: config::Options,
     let host = match Target::search(config::host_triple()) {
         Ok(t) => t,
         Err(e) => {
-            panic!(span_diagnostic.fatal(&format!("Error loading host specification: {}", e)));
+            span_diagnostic.fatal(&format!("Error loading host specification: {}", e)).raise();
         }
     };
     let target_cfg = config::build_target_config(&sopts, &span_diagnostic);
@@ -945,7 +945,7 @@ pub fn build_session_(sopts: config::Options,
     let working_dir = match env::current_dir() {
         Ok(dir) => dir,
         Err(e) => {
-            panic!(p_s.span_diagnostic.fatal(&format!("Current directory is invalid: {}", e)))
+            p_s.span_diagnostic.fatal(&format!("Current directory is invalid: {}", e)).raise()
         }
     };
     let working_dir = file_path_mapping.map_prefix(working_dir);
@@ -1076,7 +1076,7 @@ pub fn early_error(output: config::ErrorOutputType, msg: &str) -> ! {
     };
     let handler = errors::Handler::with_emitter(true, false, emitter);
     handler.emit(&MultiSpan::new(), msg, errors::Level::Fatal);
-    panic!(errors::FatalError);
+    errors::FatalError.raise();
 }
 
 pub fn early_warn(output: config::ErrorOutputType, msg: &str) {

src/librustc_driver/lib.rs

@@ -87,11 +87,11 @@ use std::env;
 use std::ffi::OsString;
 use std::io::{self, Read, Write};
 use std::iter::repeat;
+use std::panic;
 use std::path::PathBuf;
 use std::process::{self, Command, Stdio};
 use std::rc::Rc;
 use std::str;
-use std::sync::{Arc, Mutex};
 use std::thread;
 
 use syntax::ast;
@@ -168,7 +168,7 @@ pub fn run<F>(run_compiler: F) -> isize
                     handler.emit(&MultiSpan::new(),
                                  "aborting due to previous error(s)",
                                  errors::Level::Fatal);
-                    exit_on_err();
+                    panic::resume_unwind(Box::new(errors::FatalErrorMarker));
                 }
             }
         }
@@ -1228,27 +1228,16 @@ pub fn in_rustc_thread<F, R>(f: F) -> Result<R, Box<Any + Send>>
 /// The diagnostic emitter yielded to the procedure should be used for reporting
 /// errors of the compiler.
 pub fn monitor<F: FnOnce() + Send + 'static>(f: F) {
-    struct Sink(Arc<Mutex<Vec<u8>>>);
-    impl Write for Sink {
-        fn write(&mut self, data: &[u8]) -> io::Result<usize> {
-            Write::write(&mut *self.0.lock().unwrap(), data)
-        }
-        fn flush(&mut self) -> io::Result<()> {
-            Ok(())
-        }
-    }
-
-    let data = Arc::new(Mutex::new(Vec::new()));
-    let err = Sink(data.clone());
-
     let result = in_rustc_thread(move || {
-        io::set_panic(Some(box err));
         f()
     });
 
     if let Err(value) = result {
         // Thread panicked without emitting a fatal diagnostic
-        if !value.is::<errors::FatalError>() {
+        if !value.is::<errors::FatalErrorMarker>() {
+            // Emit a newline
+            eprintln!("");
+
             let emitter =
                 Box::new(errors::emitter::EmitterWriter::stderr(errors::ColorConfig::Auto,
                                                                 None,
@@ -1273,22 +1262,12 @@ pub fn monitor<F: FnOnce() + Send + 'static>(f: F) {
                              &note,
                              errors::Level::Note);
             }
-
-            eprintln!("{}", str::from_utf8(&data.lock().unwrap()).unwrap());
         }
 
-        exit_on_err();
+        panic::resume_unwind(Box::new(errors::FatalErrorMarker));
     }
 }
 
-fn exit_on_err() -> ! {
-    // Panic so the process returns a failure code, but don't pollute the
-    // output with some unnecessary panic messages, we've already
-    // printed everything that we needed to.
-    io::set_panic(Some(box io::sink()));
-    panic!();
-}
-
 #[cfg(stage0)]
 pub fn diagnostics_registry() -> errors::registry::Registry {
     use errors::registry::Registry;

src/librustc_errors/lib.rs

@@ -19,6 +19,7 @@
 #![cfg_attr(unix, feature(libc))]
 #![feature(conservative_impl_trait)]
 #![feature(i128_type)]
+#![feature(optin_builtin_traits)]
 
 extern crate term;
 #[cfg(unix)]
@@ -44,6 +45,7 @@ use std::rc::Rc;
 use std::{error, fmt};
 use std::sync::atomic::AtomicUsize;
 use std::sync::atomic::Ordering::SeqCst;
+use std::panic;
 
 mod diagnostic;
 mod diagnostic_builder;
@@ -201,6 +203,18 @@ impl CodeSuggestion {
 #[must_use]
 pub struct FatalError;
 
+pub struct FatalErrorMarker;
+
+// Don't implement Send on FatalError. This makes it impossible to panic!(FatalError).
+// We don't want to invoke the panic handler and print a backtrace for fatal errors.
+impl !Send for FatalError {}
+
+impl FatalError {
+    pub fn raise(self) -> ! {
+        panic::resume_unwind(Box::new(FatalErrorMarker))
+    }
+}
+
 impl fmt::Display for FatalError {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         write!(f, "parser fatal error")
@@ -539,7 +553,7 @@ impl Handler {
             }
         }
 
-        panic!(self.fatal(&s));
+        self.fatal(&s).raise();
     }
     pub fn emit(&self, msp: &MultiSpan, msg: &str, lvl: Level) {
         if lvl == Warning && !self.flags.can_emit_warnings {

src/librustc_trans/back/write.rs

@@ -155,7 +155,7 @@ fn get_llvm_opt_size(optimize: config::OptLevel) -> llvm::CodeGenOptSize {
 
 pub fn create_target_machine(sess: &Session) -> TargetMachineRef {
     target_machine_factory(sess)().unwrap_or_else(|err| {
-        panic!(llvm_err(sess.diagnostic(), err))
+        llvm_err(sess.diagnostic(), err).raise()
     })
 }
 
@@ -582,7 +582,7 @@ fn generate_lto_work(cgcx: &CodegenContext,
         lto::LTOMode::JustThisCrate
     };
     let lto_modules = lto::run(cgcx, modules, mode, &mut timeline)
-        .unwrap_or_else(|e| panic!(e));
+        .unwrap_or_else(|e| e.raise());
 
     lto_modules.into_iter().map(|module| {
         let cost = module.cost();

src/libsyntax/ext/base.rs

@@ -786,7 +786,7 @@ impl<'a> ExtCtxt<'a> {
     ///   substitute; we never hit resolve/type-checking so the dummy
     ///   value doesn't have to match anything)
     pub fn span_fatal<S: Into<MultiSpan>>(&self, sp: S, msg: &str) -> ! {
-        panic!(self.parse_sess.span_diagnostic.span_fatal(sp, msg));
+        self.parse_sess.span_diagnostic.span_fatal(sp, msg).raise();
     }
 
     /// Emit `msg` attached to `sp`, without immediately stopping

src/libsyntax/ext/expand.rs

@@ -455,7 +455,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                 suggested_limit));
             err.emit();
             self.cx.trace_macros_diag();
-            panic!(FatalError);
+            FatalError.raise();
         }
 
         Some(result)

src/libsyntax/ext/source_util.rs

@@ -116,9 +116,10 @@ pub fn expand_include<'cx>(cx: &'cx mut ExtCtxt, sp: Span, tts: &[tokenstream::T
             while self.p.token != token::Eof {
                 match panictry!(self.p.parse_item()) {
                     Some(item) => ret.push(item),
-                    None => panic!(self.p.diagnostic().span_fatal(self.p.span,
+                    None => self.p.diagnostic().span_fatal(self.p.span,
                                                            &format!("expected item, found `{}`",
-                                                                    self.p.this_token_to_string())))
+                                                                    self.p.this_token_to_string()))
+                                               .raise()
                 }
             }
             Some(ret)

src/libsyntax/ext/tt/macro_parser.rs

@@ -573,15 +573,15 @@ fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
             Some(i) => token::NtItem(i),
             None => {
                 p.fatal("expected an item keyword").emit();
-                panic!(FatalError);
+                FatalError.raise();
             }
         },
         "block" => token::NtBlock(panictry!(p.parse_block())),
         "stmt" => match panictry!(p.parse_stmt()) {
             Some(s) => token::NtStmt(s),
             None => {
                 p.fatal("expected a statement").emit();
-                panic!(FatalError);
+                FatalError.raise();
             }
         },
         "pat" => token::NtPat(panictry!(p.parse_pat())),
@@ -597,7 +597,7 @@ fn parse_nt<'a>(p: &mut Parser<'a>, sp: Span, name: &str) -> Nonterminal {
                 let token_str = pprust::token_to_string(&p.token);
                 p.fatal(&format!("expected ident, found {}",
                                  &token_str[..])).emit();
-                panic!(FatalError)
+                FatalError.raise()
             }
         },
         "path" => token::NtPath(panictry!(p.parse_path_common(PathStyle::Type, false))),

src/libsyntax/ext/tt/macro_rules.rs

@@ -222,10 +222,10 @@ pub fn compile(sess: &ParseSess, features: &RefCell<Features>, def: &ast::Item)
         Success(m) => m,
         Failure(sp, tok) => {
             let s = parse_failure_msg(tok);
-            panic!(sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s));
+            sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
         }
         Error(sp, s) => {
-            panic!(sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s));
+            sess.span_diagnostic.span_fatal(sp.substitute_dummy(def.span), &s).raise();
         }
     };
 

src/libsyntax/feature_gate.rs

@@ -1954,7 +1954,7 @@ impl FeatureChecker {
                 .span_note(ca_span, "`#![feature(custom_attribute)]` declared here")
                 .emit();
 
-            panic!(FatalError);
+            FatalError.raise();
         }
 
         if let (Some(span), None) = (self.copy_closures, self.clone_closures) {
@@ -1963,7 +1963,7 @@ impl FeatureChecker {
                   .span_note(span, "`#![feature(copy_closures)]` declared here")
                   .emit();
 
-            panic!(FatalError);
+            FatalError.raise();
         }
     }
 }

src/libsyntax/lib.rs

@@ -54,7 +54,7 @@ macro_rules! panictry {
             Ok(e) => e,
             Err(mut e) => {
                 e.emit();
-                panic!(FatalError);
+                FatalError.raise()
             }
         }
     })

src/libsyntax/parse/lexer/comments.rs

@@ -265,7 +265,7 @@ fn read_block_comment(rdr: &mut StringReader,
         while level > 0 {
             debug!("=== block comment level {}", level);
             if rdr.is_eof() {
-                panic!(rdr.fatal("unterminated block comment"));
+                rdr.fatal("unterminated block comment").raise();
             }
             if rdr.ch_is('\n') {
                 trim_whitespace_prefix_and_push_line(&mut lines, curr_line, col);