Improve behavior on MS-Windows when stdout is redirected to a pipe.

5 files changed, 40 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 9bed030f..ecd371ba 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2016-11-04  Eli Zaretskii  <eliz@gnu.org>
+
+	* builtin.c (efwrite) [__MINGW32__]: Call w32_maybe_set_errno if
+	errno is not set or set to EINVAL.
+
+	* nonposix.h (w32_maybe_set_errno) [__MINGW32__]: Add prototype.
+
 2016-10-26         Arnold D. Robbins     <arnold@skeeve.com>
 
 	* io.c (init_awkpath): Set max path len for leading separator.
diff --git a/builtin.c b/builtin.c
index 0163b81c..18c01f6e 100644
--- a/builtin.c
+++ b/builtin.c
@@ -125,6 +125,10 @@ efwrite(const void *ptr,
 	return;
 
 wrerror:
+#ifdef __MINGW32__
+	if (errno == 0 || errno == EINVAL)
+		w32_maybe_set_errno();
+#endif
 	/* die silently on EPIPE to stdout */
 	if (fp == stdout && errno == EPIPE)
 		gawk_exit(EXIT_FATAL);
diff --git a/nonposix.h b/nonposix.h
index 3aae512c..b3497891 100644
--- a/nonposix.h
+++ b/nonposix.h
@@ -55,6 +55,7 @@ unsigned int getegid (void);
 /* gawkmisc.pc */
 int unsetenv (const char *);
 int setenv (const char *, const char *, int);
+void w32_maybe_set_errno (void);
 #endif	/* __MINGW32__ */
 
 #if defined(VMS) || defined(__DJGPP__) || defined(__MINGW32__)
diff --git a/pc/ChangeLog b/pc/ChangeLog
index 7ba5fd9c..1ff3bb1f 100644
--- a/pc/ChangeLog
+++ b/pc/ChangeLog
@@ -1,3 +1,8 @@
+2016-11-04  Eli Zaretskii  <eliz@gnu.org>
+
+	* gawkmisc.pc (w32_maybe_set_errno) [__MINGW32__]: New function,
+	to correct errno when it is not set to a useful value.
+
 2016-09-24  Eli Zaretskii  <eliz@gnu.org>
 
 	Fix compilation warnings on MinGW with the latest runtime.
diff --git a/pc/gawkmisc.pc b/pc/gawkmisc.pc
index 9939fb48..817e8167 100644
--- a/pc/gawkmisc.pc
+++ b/pc/gawkmisc.pc
@@ -1,6 +1,4 @@
-/*
- * gawkmisc.c --- miscellaneous gawk routines that are OS specific.
- */
+/* gawkmisc.c --- miscellaneous gawk routines that are OS specific. -*-C-*- */
 
 /* 
  * Copyright (C) 1986, 1988, 1989, 1991 - 2003, 2012, 2016
@@ -897,6 +895,28 @@ w32_status_to_termsig (unsigned status)
   return SIGTERM;
 }
 
+void
+w32_maybe_set_errno (void)
+{
+  DWORD w32err = GetLastError ();
+
+  switch (w32err)
+    {
+      /* When stdout is redirected to a pipe, and the program that
+	 reads the pipe (e.g., a pager) exits, Windows doesn't set
+	 errno to a useful value.  Help it DTRT.  */
+      case ERROR_BAD_PIPE:
+      case ERROR_PIPE_BUSY:
+      case ERROR_NO_DATA:
+      case ERROR_PIPE_NOT_CONNECTED:
+	errno = EPIPE;
+	break;
+      default:
+	errno = EINVAL;
+	break;
+    }
+}
+
 #endif	/* __MINGW32__ */
 
 #if defined(__DJGPP__) || defined(__MINGW32__) || defined(__EMX__)