unix_sigpipe: Add test for SIGPIPE disposition in child processes

For robustness, also test the disposition in our own process even if
tests in `tests/ui/attributes/unix_sigpipe` already covers it.

tests/run-make/sigpipe-in-child-processes/Makefile

@@ -0,0 +1,15 @@
+# ignore-cross-compile because we run the compiled code
+# only-unix
+
+# See main.rs for a description of this test.
+
+include ../tools.mk
+
+all:
+	$(RUSTC) assert-sigpipe-disposition.rs -o $(TMPDIR)/assert-sigpipe-disposition;
+	for revision in default sig_dfl sig_ign inherit; do \
+		echo -n "Testing revision $$revision ... "; \
+		$(RUSTC) main.rs --cfg $$revision -o $(TMPDIR)/main.$$revision || exit 1; \
+		$(TMPDIR)/main.$$revision $(TMPDIR)/assert-sigpipe-disposition || exit 1; \
+		echo "ok"; \
+	done

tests/run-make/sigpipe-in-child-processes/assert-sigpipe-disposition.rs

@@ -0,0 +1,25 @@
+#![feature(start, rustc_private)]
+
+extern crate libc;
+
+// Use #[start] so we don't have a runtime that messes with SIGPIPE.
+#[start]
+fn start(argc: isize, argv: *const *const u8) -> isize {
+    assert_eq!(argc, 2, "Must pass SIG_IGN or SIG_DFL as first arg");
+    let expected =
+        match unsafe { std::ffi::CStr::from_ptr(*argv.offset(1) as *const i8) }.to_str().unwrap() {
+            "SIG_IGN" => libc::SIG_IGN,
+            "SIG_DFL" => libc::SIG_DFL,
+            arg => panic!("Must pass SIG_IGN or SIG_DFL as first arg. Got: {}", arg),
+        };
+
+    let actual = unsafe {
+        let mut actual: libc::sigaction = std::mem::zeroed();
+        libc::sigaction(libc::SIGPIPE, std::ptr::null(), &mut actual);
+        actual.sa_sigaction
+    };
+
+    assert_eq!(actual, expected, "actual and expected SIGPIPE disposition in child differs");
+
+    return 0;
+}

tests/run-make/sigpipe-in-child-processes/main.rs

@@ -0,0 +1,51 @@
+// Checks the signal disposition of `SIGPIPE` in child processes, and in our own
+// process for robustness. Without any `unix_sigpipe` attribute, `SIG_IGN` is
+// the default. But there is a difference in how `SIGPIPE` is treated in child
+// processes with and without the attribute. Search for
+// `unix_sigpipe_attr_specified()` in the code base to learn more.
+//
+// Note that there are many other tests for `unix_sigpipe` in
+// tests/ui/attributes/unix_sigpipe.
+
+#![feature(rustc_private)]
+#![cfg_attr(any(sig_dfl, sig_ign, inherit), feature(unix_sigpipe))]
+
+extern crate libc;
+
+#[cfg_attr(sig_dfl, unix_sigpipe = "sig_dfl")]
+#[cfg_attr(sig_ign, unix_sigpipe = "sig_ign")]
+#[cfg_attr(inherit, unix_sigpipe = "inherit")]
+fn main() {
+    // By default, we get SIG_IGN but the child gets SIG_DFL.
+    #[cfg(default)]
+    let (we_expect, child_expects) = (libc::SIG_IGN, libc::SIG_DFL);
+
+    // With #[unix_sigpipe = "sig_dfl"] we get SIG_DFL and the child does too.
+    #[cfg(sig_dfl)]
+    let (we_expect, child_expects) = (libc::SIG_DFL, libc::SIG_DFL);
+
+    // With #[unix_sigpipe = "sig_ign"] we get SIG_IGN and the child does too.
+    #[cfg(sig_ign)]
+    let (we_expect, child_expects) = (libc::SIG_IGN, libc::SIG_IGN);
+
+    // With #[unix_sigpipe = "inherit"] we get SIG_DFL and the child does too.
+    #[cfg(inherit)]
+    let (we_expect, child_expects) = (libc::SIG_DFL, libc::SIG_DFL);
+
+    let actual = unsafe {
+        let mut actual: libc::sigaction = std::mem::zeroed();
+        libc::sigaction(libc::SIGPIPE, std::ptr::null(), &mut actual);
+        actual.sa_sigaction
+    };
+    assert_eq!(actual, we_expect, "we did not get the SIGPIPE disposition we expect");
+
+    let child_program = std::env::args().nth(1).unwrap();
+    let child_expects = match child_expects {
+        libc::SIG_DFL => "SIG_DFL",
+        libc::SIG_IGN => "SIG_IGN",
+        _ => unreachable!(),
+    };
+    assert!(
+        std::process::Command::new(child_program).arg(child_expects).status().unwrap().success()
+    );
+}