Support `#[unix_sigpipe = "inherit|sig_dfl|sig_ign"]` on `fn main()`

This makes it possible to instruct libstd to never touch the signal
handler for `SIGPIPE`, which makes programs pipeable by default (e.g.
with `./your-program | head -n 1`) without `ErrorKind::BrokenPipe`
errors.

2 files changed, 31 insertions, 1 deletions

diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 162fc9aa0a6..e7c8538300e 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -36,6 +36,8 @@ use std::iter::{self, FromIterator};
 use std::path::{Path, PathBuf};
 use std::str::{self, FromStr};
 
+pub mod sigpipe;
+
 /// The different settings that the `-C strip` flag can have.
 #[derive(Clone, Copy, PartialEq, Hash, Debug)]
 pub enum Strip {
@@ -798,7 +800,15 @@ impl UnstableOptions {
 // The type of entry function, so users can have their own entry functions
 #[derive(Copy, Clone, PartialEq, Hash, Debug, HashStable_Generic)]
 pub enum EntryFnType {
-    Main,
+    Main {
+        /// Specifies what to do with `SIGPIPE` before calling `fn main()`.
+        ///
+        /// What values that are valid and what they mean must be in sync
+        /// across rustc and libstd, but we don't want it public in libstd,
+        /// so we take a bit of an unusual approach with simple constants
+        /// and an `include!()`.
+        sigpipe: u8,
+    },
     Start,
 }
 
diff --git a/compiler/rustc_session/src/config/sigpipe.rs b/compiler/rustc_session/src/config/sigpipe.rs
new file mode 100644
index 00000000000..31a3d9de05b
--- /dev/null
+++ b/compiler/rustc_session/src/config/sigpipe.rs
@@ -0,0 +1,20 @@
+/// Do not touch `SIGPIPE`. Use whatever the parent process uses.
+#[allow(dead_code)]
+pub const INHERIT: u8 = 1;
+
+/// Change `SIGPIPE` to `SIG_IGN` so that failed writes results in `EPIPE`
+/// that are eventually converted to `ErrorKind::BrokenPipe`.
+#[allow(dead_code)]
+pub const SIG_IGN: u8 = 2;
+
+/// Change `SIGPIPE` to `SIG_DFL` so that the process is killed when trying
+/// to write to a closed pipe. This is usually the desired behavior for CLI
+/// apps that produce textual output that you want to pipe to other programs
+/// such as `head -n 1`.
+#[allow(dead_code)]
+pub const SIG_DFL: u8 = 3;
+
+/// `SIG_IGN` has been the Rust default since 2014. See
+/// <https://github.com/rust-lang/rust/issues/62569>.
+#[allow(dead_code)]
+pub const DEFAULT: u8 = SIG_IGN;