maybe_flush_or_die: move a too-loose Windows specific error

 check to compat

Commit b2f5e26 (Windows: Work around an oddity when a pipe with no reader
is written to) introduced a check for EINVAL after fflush() to fight
spurious "Invalid argument" errors on Windows when a pipe was broken. But
this check may hide real errors on systems that do not have the this odd
behavior. Introduce an fflush wrapper in compat/mingw.* so that the treatment
is only applied on Windows.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -335,6 +335,28 @@ FILE *mingw_freopen (const char *filename, const char *otype, FILE *stream)
 	return freopen(filename, otype, stream);
 }
 
+#undef fflush
+int mingw_fflush(FILE *stream)
+{
+	int ret = fflush(stream);
+
+	/*
+	 * write() is used behind the scenes of stdio output functions.
+	 * Since git code does not check for errors after each stdio write
+	 * operation, it can happen that write() is called by a later
+	 * stdio function even if an earlier write() call failed. In the
+	 * case of a pipe whose readable end was closed, only the first
+	 * call to write() reports EPIPE on Windows. Subsequent write()
+	 * calls report EINVAL. It is impossible to notice whether this
+	 * fflush invocation triggered such a case, therefore, we have to
+	 * catch all EINVAL errors whole-sale.
+	 */
+	if (ret && errno == EINVAL)
+		errno = EPIPE;
+
+	return ret;
+}
+
 /*
  * The unit of FILETIME is 100-nanoseconds since January 1, 1601, UTC.
  * Returns the 100-nanoseconds ("hekto nanoseconds") since the epoch.

compat/mingw.h

@@ -185,6 +185,9 @@ FILE *mingw_fopen (const char *filename, const char *otype);
 FILE *mingw_freopen (const char *filename, const char *otype, FILE *stream);
 #define freopen mingw_freopen
 
+int mingw_fflush(FILE *stream);
+#define fflush mingw_fflush
+
 char *mingw_getcwd(char *pointer, int len);
 #define getcwd mingw_getcwd
 

write_or_die.c

@@ -34,12 +34,7 @@ void maybe_flush_or_die(FILE *f, const char *desc)
 			return;
 	}
 	if (fflush(f)) {
-		/*
-		 * On Windows, EPIPE is returned only by the first write()
-		 * after the reading end has closed its handle; subsequent
-		 * write()s return EINVAL.
-		 */
-		if (errno == EPIPE || errno == EINVAL)
+		if (errno == EPIPE)
 			exit(0);
 		die_errno("write failure on '%s'", desc);
 	}