error_routine: use parent's stderr if exec fails

The new process's error output may be redirected elsewhere, but if
the exec fails, output should still go to the parent's stderr. This
has already been done for the die_routine. Do the same for
error_routine.

Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Clemens Buchacher

git-compat-util.h

@@ -236,6 +236,7 @@ extern char *gitbasename(char *);
 
 /* General helper functions */
 extern void vreportf(const char *prefix, const char *err, va_list params);
+extern void vwritef(int fd, const char *prefix, const char *err, va_list params);
 extern NORETURN void usage(const char *err);
 extern NORETURN void usagef(const char *err, ...) __attribute__((format (printf, 1, 2)));
 extern NORETURN void die(const char *err, ...) __attribute__((format (printf, 1, 2)));
@@ -244,6 +245,7 @@ extern int error(const char *err, ...) __attribute__((format (printf, 1, 2)));
 extern void warning(const char *err, ...) __attribute__((format (printf, 1, 2)));
 
 extern void set_die_routine(NORETURN_PTR void (*routine)(const char *err, va_list params));
+extern void set_error_routine(void (*routine)(const char *err, va_list params));
 
 extern int prefixcmp(const char *str, const char *prefix);
 extern int suffixcmp(const char *str, const char *suffix);

run-command.c

@@ -77,16 +77,14 @@ static void notify_parent(void)
 
 static NORETURN void die_child(const char *err, va_list params)
 {
-	char msg[4096];
-	int len = vsnprintf(msg, sizeof(msg), err, params);
-	if (len > sizeof(msg))
-		len = sizeof(msg);
-
-	write_in_full(child_err, "fatal: ", 7);
-	write_in_full(child_err, msg, len);
-	write_in_full(child_err, "\n", 1);
+	vwritef(child_err, "fatal: ", err, params);
 	exit(128);
 }
+
+static void error_child(const char *err, va_list params)
+{
+	vwritef(child_err, "error: ", err, params);
+}
 #endif
 
 static inline void set_cloexec(int fd)
@@ -217,6 +215,7 @@ int start_command(struct child_process *cmd)
 			set_cloexec(child_err);
 		}
 		set_die_routine(die_child);
+		set_error_routine(error_child);
 
 		close(notify_pipe[0]);
 		set_cloexec(notify_pipe[1]);

usage.c

@@ -4,6 +4,7 @@
  * Copyright (C) Linus Torvalds, 2005
  */
 #include "git-compat-util.h"
+#include "cache.h"
 
 void vreportf(const char *prefix, const char *err, va_list params)
 {
@@ -12,6 +13,18 @@ void vreportf(const char *prefix, const char *err, va_list params)
 	fprintf(stderr, "%s%s\n", prefix, msg);
 }
 
+void vwritef(int fd, const char *prefix, const char *err, va_list params)
+{
+	char msg[4096];
+	int len = vsnprintf(msg, sizeof(msg), err, params);
+	if (len > sizeof(msg))
+		len = sizeof(msg);
+
+	write_in_full(fd, prefix, strlen(prefix));
+	write_in_full(fd, msg, len);
+	write_in_full(fd, "\n", 1);
+}
+
 static NORETURN void usage_builtin(const char *err, va_list params)
 {
 	vreportf("usage: ", err, params);
@@ -46,6 +59,11 @@ void set_die_routine(NORETURN_PTR void (*routine)(const char *err, va_list param
 	die_routine = routine;
 }
 
+void set_error_routine(void (*routine)(const char *err, va_list params))
+{
+	error_routine = routine;
+}
+
 void NORETURN usagef(const char *err, ...)
 {
 	va_list params;