Revert "Reapply: Add an error message to the default SIGPIPE handler"

[void]

Summary

This patch is spamming compiles with unhelpful and confusing messages.
E.g. the Linux kernel uses "grep -q" in several places. It's meant to
quit with a return code of zero when the first match is found. This can
cause a SIGPIPE signal, but that's expected. Worse, there's no way to
turn this error message off. We can only pipe it to /dev/null, which is
a bit awkward.

Is UNIX03 conformance something Clang is striving for? If so, then we
need a much better solution than to emit an error message that we can't
quiet.

This reverts commit b89bcefa6202e310eb3167dd1c37f1807377ec8d.

Link: https://github.com/ClangBuiltLinux/linux/issues/1651
Link: https://github.com/llvm/llvm-project/issues/59037

[kees]

Looks good. Likely future work here would be to examine why the EX_IOERR exit is being exposed instead of just leaving SIGPIPE set to SIG_DFLT. But that's a separate issue entirely. :)

[nickdesaulniers]

In D138244#3935296, @kees wrote:

Looks good. Likely future work here would be to examine why the EX_IOERR exit is being exposed instead of just leaving SIGPIPE set to SIG_DFLT. But that's a separate issue entirely. :)

I think I added something like this: https://reviews.llvm.org/D53000 where in clang we need to check that return code in other frontends...

llvm/lib/Support/Unix/Signals.inc

 }
 
 void llvm::sys::SetOneShotPipeSignalFunction(void (*Handler)()) {
   OneShotPipeSignalFunction.exchange(Handler);
   RegisterHandlers();
 }
 
 void llvm::sys::DefaultOneShotPipeSignalHandler() {
-  // UNIX03 conformance requires a non-zero exit code and an error message
-  // to stderr when writing to a closed stdout fails.
-  errs() << "error: write on a pipe with no reader\n";
-
   // Send a special return code that drivers can check for, from sysexits.h.
   exit(EX_IOERR);
 }
 
 // The public API
 bool llvm::sys::RemoveFileOnSignal(StringRef Filename,
                                    std::string* ErrMsg) {
   // Ensure that cleanup will occur as soon as one file is added.

llvm/test/Support/unix03-sigpipe-exit.test

-## Test that when writing to a closed stdout, LLVM tools finish with a non-zero
-## exit code and an error message on stderr. The test uses llvm-cxxfilt, but
-## it's a logic from the default SIGPIPE handler, so it applies to all the tools.
-## This is required for UNIX03 conformance.
-
-# UNSUPPORTED: system-windows
-
-# RUN: not %python %s llvm-cxxfilt 2>&1 | FileCheck %s
-# CHECK: error: write on a pipe with no reader
-
-import subprocess
-import sys
-
-with subprocess.Popen([sys.argv[1]], stdout=subprocess.PIPE, stdin=subprocess.PIPE) as process:
-  process.stdout.close()
-
-  # llvm-cxxfilt with no extra arguments runs interactively and writes input
-  # to output. Writing continuously to stdin should trigger SIGPIPE when the
-  # subprocess attempts to write out bytes to a closed stdout.
-  try:
-    while True:
-      process.stdin.write("foo\n".encode("utf-8"))
-  except BrokenPipeError:
-    # Clear stdin, pipe is broken and closing it on cleanup will raise an exception.
-    process.stdin = None
-sys.exit(process.returncode)