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.

28 files changed, 310 insertions, 0 deletions

diff --git a/src/doc/unstable-book/src/language-features/unix-sigpipe.md b/src/doc/unstable-book/src/language-features/unix-sigpipe.md
new file mode 100644
index 00000000000..aa39b6eb288
--- /dev/null
+++ b/src/doc/unstable-book/src/language-features/unix-sigpipe.md
@@ -0,0 +1,54 @@
+# `unix_sigpipe`
+
+The tracking issue for this feature is: [#97889]
+
+[#97889]: https://github.com/rust-lang/rust/issues/97889
+
+---
+
+The `#[unix_sigpipe = "..."]` attribute on `fn main()` can be used to specify how libstd shall setup `SIGPIPE` on Unix platforms before invoking `fn main()`. This attribute is ignored on non-Unix targets. There are three variants:
+* `#[unix_sigpipe = "inherit"]`
+* `#[unix_sigpipe = "sig_dfl"]`
+* `#[unix_sigpipe = "sig_ign"]`
+
+## `#[unix_sigpipe = "inherit"]`
+
+Leave `SIGPIPE` untouched before entering `fn main()`. Unless the parent process has changed the default `SIGPIPE` handler from `SIG_DFL` to something else, this will behave the same as `#[unix_sigpipe = "sig_dfl"]`.
+
+## `#[unix_sigpipe = "sig_dfl"]`
+
+Set the `SIGPIPE` handler to `SIG_DFL`. This will result in your program getting killed if it tries to write to a closed pipe. This is normally what you want if your program produces textual output.
+
+### Example
+
+```rust,no_run
+#![feature(unix_sigpipe)]
+#[unix_sigpipe = "sig_dfl"]
+fn main() { loop { println!("hello world"); } }
+```
+
+```bash
+% ./main | head -n 1
+hello world
+```
+
+## `#[unix_sigpipe = "sig_ign"]`
+
+Set the `SIGPIPE` handler to `SIG_IGN` before invoking `fn main()`. This will result in `ErrorKind::BrokenPipe` errors if you program tries to write to a closed pipe. This is normally what you want if you for example write socket servers, socket clients, or pipe peers.
+
+This is what libstd has done by default since 2014. Omitting `#[unix_sigpipe = "..."]` is the same as having `#[unix_sigpipe = "sig_ign"]`.
+
+### Example
+
+```rust,no_run
+#![feature(unix_sigpipe)]
+#[unix_sigpipe = "sig_ign"]
+fn main() { loop { println!("hello world"); } }
+```
+
+```bash
+% ./main | head -n 1
+hello world
+thread 'main' panicked at 'failed printing to stdout: Broken pipe (os error 32)', library/std/src/io/stdio.rs:1016:9
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+```
diff --git a/src/test/ui/attributes/unix_sigpipe/auxiliary/sigpipe-utils.rs b/src/test/ui/attributes/unix_sigpipe/auxiliary/sigpipe-utils.rs
new file mode 100644
index 00000000000..07ff051f789
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/auxiliary/sigpipe-utils.rs
@@ -0,0 +1,26 @@
+#![feature(rustc_private)]
+extern crate libc;
+
+/// So tests don't have to bring libc in scope themselves
+pub enum SignalHandler {
+    Ignore,
+    Default,
+}
+
+/// Helper to assert that [`libc::SIGPIPE`] has the expected signal handler.
+pub fn assert_sigpipe_handler(expected_handler: SignalHandler) {
+    #[cfg(unix)]
+    #[cfg(not(any(target_os = "emscripten", target_os = "fuchsia", target_os = "horizon")))]
+    {
+        let prev = unsafe { libc::signal(libc::SIGPIPE, libc::SIG_IGN) };
+
+        let expected = match expected_handler {
+            SignalHandler::Ignore => libc::SIG_IGN,
+            SignalHandler::Default => libc::SIG_DFL,
+        };
+        assert_eq!(prev, expected);
+
+        // Unlikely to matter, but restore the old value anyway
+        unsafe { libc::signal(libc::SIGPIPE, prev); };
+    }
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-crate.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-crate.rs
new file mode 100644
index 00000000000..d6d020c52b2
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-crate.rs
@@ -0,0 +1,4 @@
+#![feature(unix_sigpipe)]
+#![unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute cannot be used at crate level
+
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-crate.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-crate.stderr
new file mode 100644
index 00000000000..a1fb4d6787c
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-crate.stderr
@@ -0,0 +1,13 @@
+error: `unix_sigpipe` attribute cannot be used at crate level
+  --> $DIR/unix_sigpipe-crate.rs:2:1
+   |
+LL | #![unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: perhaps you meant to use an outer attribute
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.rs
new file mode 100644
index 00000000000..294cb38526b
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.rs
@@ -0,0 +1,5 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "sig_ign"]
+#[unix_sigpipe = "inherit"] //~ error: multiple `unix_sigpipe` attributes
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.stderr
new file mode 100644
index 00000000000..2362c17a090
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-duplicates.stderr
@@ -0,0 +1,14 @@
+error: multiple `unix_sigpipe` attributes
+  --> $DIR/unix_sigpipe-duplicates.rs:4:1
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
+   |
+note: attribute also specified here
+  --> $DIR/unix_sigpipe-duplicates.rs:3:1
+   |
+LL | #[unix_sigpipe = "sig_ign"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-error.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-error.rs
new file mode 100644
index 00000000000..0a42a5b5ef1
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-error.rs
@@ -0,0 +1,13 @@
+// run-pass
+// aux-build:sigpipe-utils.rs
+
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "sig_ign"]
+fn main() {
+    extern crate sigpipe_utils;
+
+    // #[unix_sigpipe = "sig_ign"] is active, so the legacy behavior of ignoring
+    // SIGPIPE shall be in effect
+    sigpipe_utils::assert_sigpipe_handler(sigpipe_utils::SignalHandler::Ignore);
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-inherit.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-inherit.rs
new file mode 100644
index 00000000000..4f864807752
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-inherit.rs
@@ -0,0 +1,14 @@
+// run-pass
+// aux-build:sigpipe-utils.rs
+
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "inherit"]
+fn main() {
+    extern crate sigpipe_utils;
+
+    // #[unix_sigpipe = "inherit"] is active, so SIGPIPE shall NOT be ignored,
+    // instead the default handler shall be installed. (We assume that the
+    // process that runs these tests have the default handler.)
+    sigpipe_utils::assert_sigpipe_handler(sigpipe_utils::SignalHandler::Default);
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-list.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-list.rs
new file mode 100644
index 00000000000..b5ebc07a043
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-list.rs
@@ -0,0 +1,4 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe(inherit)] //~ error: malformed `unix_sigpipe` attribute input
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-list.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-list.stderr
new file mode 100644
index 00000000000..59a87e13918
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-list.stderr
@@ -0,0 +1,15 @@
+error: malformed `unix_sigpipe` attribute input
+  --> $DIR/unix_sigpipe-list.rs:3:1
+   |
+LL | #[unix_sigpipe(inherit)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: the following are the possible correct uses
+   |
+LL | #[unix_sigpipe = "inherit|sig_ign|sig_dfl"]
+   | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+LL | #[unix_sigpipe]
+   | ~~~~~~~~~~~~~~~
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.rs
new file mode 100644
index 00000000000..cde6719fc9c
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.rs
@@ -0,0 +1,6 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
+fn f() {}
+
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.stderr
new file mode 100644
index 00000000000..c4b81118c9f
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-main-fn.stderr
@@ -0,0 +1,8 @@
+error: `unix_sigpipe` attribute can only be used on `fn main()`
+  --> $DIR/unix_sigpipe-non-main-fn.rs:3:1
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.rs
new file mode 100644
index 00000000000..16f7276398e
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.rs
@@ -0,0 +1,8 @@
+#![feature(unix_sigpipe)]
+
+mod m {
+    #[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on root `fn main()`
+    fn main() {}
+}
+
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.stderr
new file mode 100644
index 00000000000..a04f605edc2
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-non-root-main.stderr
@@ -0,0 +1,8 @@
+error: `unix_sigpipe` attribute can only be used on root `fn main()`
+  --> $DIR/unix_sigpipe-non-root-main.rs:4:5
+   |
+LL |     #[unix_sigpipe = "inherit"]
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-not-used.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-not-used.rs
new file mode 100644
index 00000000000..100b4ce9f74
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-not-used.rs
@@ -0,0 +1,9 @@
+// run-pass
+// aux-build:sigpipe-utils.rs
+
+fn main() {
+    extern crate sigpipe_utils;
+
+    // SIGPIPE shall be ignored since #[unix_sigpipe = "..."] is not used
+    sigpipe_utils::assert_sigpipe_handler(sigpipe_utils::SignalHandler::Ignore);
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-only-feature.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-only-feature.rs
new file mode 100644
index 00000000000..b5adc2e5572
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-only-feature.rs
@@ -0,0 +1,13 @@
+// run-pass
+// aux-build:sigpipe-utils.rs
+
+#![feature(unix_sigpipe)]
+
+fn main() {
+    extern crate sigpipe_utils;
+
+    // Only #![feature(unix_sigpipe)] is enabled, not #[unix_sigpipe = "..."].
+    // This shall not change any behavior, so we still expect SIGPIPE to be
+    // ignored
+    sigpipe_utils::assert_sigpipe_handler(sigpipe_utils::SignalHandler::Ignore);
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-rustc_main.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-rustc_main.rs
new file mode 100644
index 00000000000..6befb9e9565
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-rustc_main.rs
@@ -0,0 +1,15 @@
+// run-pass
+// aux-build:sigpipe-utils.rs
+
+#![feature(unix_sigpipe)]
+#![feature(rustc_attrs)]
+
+#[unix_sigpipe = "sig_dfl"]
+#[rustc_main]
+fn rustc_main() {
+    extern crate sigpipe_utils;
+
+    // #[unix_sigpipe = "sig_dfl"] is active, so SIGPIPE handler shall be
+    // SIG_DFL. Note that we have a #[rustc_main], but it should still work.
+    sigpipe_utils::assert_sigpipe_handler(sigpipe_utils::SignalHandler::Default);
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-sig_dfl.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-sig_dfl.rs
new file mode 100644
index 00000000000..238c0d57a68
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-sig_dfl.rs
@@ -0,0 +1,13 @@
+// run-pass
+// aux-build:sigpipe-utils.rs
+
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "sig_dfl"]
+fn main() {
+    extern crate sigpipe_utils;
+
+    // #[unix_sigpipe = "sig_dfl"] is active, so SIGPIPE shall NOT be ignored, instead
+    // the default handler shall be installed
+    sigpipe_utils::assert_sigpipe_handler(sigpipe_utils::SignalHandler::Default);
+}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-start.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-start.rs
new file mode 100644
index 00000000000..64fd5ec4f0e
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-start.rs
@@ -0,0 +1,6 @@
+#![feature(start)]
+#![feature(unix_sigpipe)]
+
+#[start]
+#[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
+fn custom_start(argc: isize, argv: *const *const u8) -> isize { 0 }
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-start.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-start.stderr
new file mode 100644
index 00000000000..2c9ce479b6c
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-start.stderr
@@ -0,0 +1,8 @@
+error: `unix_sigpipe` attribute can only be used on `fn main()`
+  --> $DIR/unix_sigpipe-start.rs:5:1
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-struct.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-struct.rs
new file mode 100644
index 00000000000..a5e47cfebc8
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-struct.rs
@@ -0,0 +1,6 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "inherit"] //~ error: `unix_sigpipe` attribute can only be used on `fn main()`
+struct S;
+
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-struct.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-struct.stderr
new file mode 100644
index 00000000000..c56ee60bb2e
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-struct.stderr
@@ -0,0 +1,8 @@
+error: `unix_sigpipe` attribute can only be used on `fn main()`
+  --> $DIR/unix_sigpipe-struct.rs:3:1
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-wrong.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-wrong.rs
new file mode 100644
index 00000000000..4ec25de00ec
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-wrong.rs
@@ -0,0 +1,4 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe = "wrong"] //~ error: valid values for `#[unix_sigpipe = "..."]` are `inherit`, `sig_ign`, or `sig_dfl`
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-wrong.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-wrong.stderr
new file mode 100644
index 00000000000..a66e45aa210
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe-wrong.stderr
@@ -0,0 +1,8 @@
+error: valid values for `#[unix_sigpipe = "..."]` are `inherit`, `sig_ign`, or `sig_dfl`
+  --> $DIR/unix_sigpipe-wrong.rs:3:1
+   |
+LL | #[unix_sigpipe = "wrong"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe.rs b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe.rs
new file mode 100644
index 00000000000..7bf1c7350c3
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe.rs
@@ -0,0 +1,4 @@
+#![feature(unix_sigpipe)]
+
+#[unix_sigpipe] //~ error: valid values for `#[unix_sigpipe = "..."]` are `inherit`, `sig_ign`, or `sig_dfl`
+fn main() {}
diff --git a/src/test/ui/attributes/unix_sigpipe/unix_sigpipe.stderr b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe.stderr
new file mode 100644
index 00000000000..1b1eda825aa
--- /dev/null
+++ b/src/test/ui/attributes/unix_sigpipe/unix_sigpipe.stderr
@@ -0,0 +1,8 @@
+error: valid values for `#[unix_sigpipe = "..."]` are `inherit`, `sig_ign`, or `sig_dfl`
+  --> $DIR/unix_sigpipe.rs:3:1
+   |
+LL | #[unix_sigpipe]
+   | ^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
diff --git a/src/test/ui/feature-gates/feature-gate-unix_sigpipe.rs b/src/test/ui/feature-gates/feature-gate-unix_sigpipe.rs
new file mode 100644
index 00000000000..46dc3f6cc17
--- /dev/null
+++ b/src/test/ui/feature-gates/feature-gate-unix_sigpipe.rs
@@ -0,0 +1,4 @@
+#![crate_type = "bin"]
+
+#[unix_sigpipe = "inherit"] //~ the `#[unix_sigpipe]` attribute is an experimental feature
+fn main () {}
diff --git a/src/test/ui/feature-gates/feature-gate-unix_sigpipe.stderr b/src/test/ui/feature-gates/feature-gate-unix_sigpipe.stderr
new file mode 100644
index 00000000000..cf3284467f7
--- /dev/null
+++ b/src/test/ui/feature-gates/feature-gate-unix_sigpipe.stderr
@@ -0,0 +1,12 @@
+error[E0658]: the `#[unix_sigpipe]` attribute is an experimental feature
+  --> $DIR/feature-gate-unix_sigpipe.rs:3:1
+   |
+LL | #[unix_sigpipe = "inherit"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #97889 <https://github.com/rust-lang/rust/issues/97889> for more information
+   = help: add `#![feature(unix_sigpipe)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.