Rollup merge of rust-lang#49606 - varkor:pipe-repair, r=alexcrichton

Prevent broken pipes causing ICEs

As the private `std::io::print_to` panics if there is an I/O error, which is used by `println!`, the compiler would ICE if one attempted to use a broken pipe (e.g. `rustc --help | false`). This introduces a new (private) macro `try_println!` which allows us to avoid this.

As a side note, it seems this macro might be useful publicly (and actually there seems to be [a crate specifically for this purpose](https://crates.io/crates/try_print/)), though that can probably be left for a future discussion.

One slight alternative approach would be to simply early exit without an error (i.e. exit code `0`), which [this comment](rust-lang#34376 (comment)) suggests is the usual approach. I've opted not to take that approach initially, because I think it's more helpful to know when there is a broken pipe.

Fixes rust-lang#34376.

src/librustc_driver/lib.rs

@@ -547,6 +547,18 @@ fn run_compiler_impl<'a>(args: &[String],
     (result, Some(sess))
 }
 
+#[cfg(unix)]
+pub fn set_sigpipe_handler() {
+    unsafe {
+        // Set the SIGPIPE signal handler, so that an EPIPE
+        // will cause rustc to terminate, as expected.
+        assert!(libc::signal(libc::SIGPIPE, libc::SIG_DFL) != libc::SIG_ERR);
+    }
+}
+
+#[cfg(windows)]
+pub fn set_sigpipe_handler() {}
+
 // Extract output directory and file from matches.
 fn make_output(matches: &getopts::Matches) -> (Option<PathBuf>, Option<PathBuf>) {
     let odir = matches.opt_str("out-dir").map(|o| PathBuf::from(&o));

src/librustdoc/lib.rs

@@ -100,6 +100,7 @@ struct Output {
 
 pub fn main() {
     const STACK_SIZE: usize = 32_000_000; // 32MB
+    rustc_driver::set_sigpipe_handler();
     env_logger::init();
     let res = std::thread::Builder::new().stack_size(STACK_SIZE).spawn(move || {
         syntax::with_globals(move || {

src/libstd/sys/unix/mod.rs

@@ -80,11 +80,11 @@ pub fn init() {
         reset_sigpipe();
     }
 
-    #[cfg(not(any(target_os = "emscripten", target_os="fuchsia")))]
+    #[cfg(not(any(target_os = "emscripten", target_os = "fuchsia")))]
     unsafe fn reset_sigpipe() {
         assert!(signal(libc::SIGPIPE, libc::SIG_IGN) != libc::SIG_ERR);
     }
-    #[cfg(any(target_os = "emscripten", target_os="fuchsia"))]
+    #[cfg(any(target_os = "emscripten", target_os = "fuchsia"))]
     unsafe fn reset_sigpipe() {}
 }
 

src/rustc/rustc.rs

@@ -23,4 +23,7 @@ extern {}
 
 extern crate rustc_driver;
 
-fn main() { rustc_driver::main() }
+fn main() {
+    rustc_driver::set_sigpipe_handler();
+    rustc_driver::main()
+}