1 files changed, 47 insertions, 4 deletions

diff --git a/usage.c b/usage.c
index cc803336bd..58fb5fff5f 100644
--- a/usage.c
+++ b/usage.c
@@ -9,30 +9,73 @@
 void vreportf(const char *prefix, const char *err, va_list params)
 {
 	char msg[4096];
-	char *p;
+	char *p, *pend = msg + sizeof(msg);
+	size_t prefix_len = strlen(prefix);
 
-	vsnprintf(msg, sizeof(msg), err, params);
-	for (p = msg; *p; p++) {
+	if (sizeof(msg) <= prefix_len) {
+		fprintf(stderr, "BUG!!! too long a prefix '%s'\n", prefix);
+		abort();
+	}
+	memcpy(msg, prefix, prefix_len);
+	p = msg + prefix_len;
+	if (vsnprintf(p, pend - p, err, params) < 0)
+		*p = '\0'; /* vsnprintf() failed, clip at prefix */
+
+	for (; p != pend - 1 && *p; p++) {
 		if (iscntrl(*p) && *p != '\t' && *p != '\n')
 			*p = '?';
 	}
-	fprintf(stderr, "%s%s\n", prefix, msg);
+
+	*(p++) = '\n'; /* we no longer need a NUL */
+	fflush(stderr);
+	write_in_full(2, msg, p - msg);
 }
 
 static NORETURN void usage_builtin(const char *err, va_list params)
 {
 	vreportf("usage: ", err, params);
+
+	/*
+	 * When we detect a usage error *before* the command dispatch in
+	 * cmd_main(), we don't know what verb to report.  Force it to this
+	 * to facilitate post-processing.
+	 */
+	trace2_cmd_name("_usage_");
+
+	/*
+	 * Currently, the (err, params) are usually just the static usage
+	 * string which isn't very useful here.  Usually, the call site
+	 * manually calls fprintf(stderr,...) with the actual detailed
+	 * syntax error before calling usage().
+	 *
+	 * TODO It would be nice to update the call sites to pass both
+	 * the static usage string and the detailed error message.
+	 */
+
 	exit(129);
 }
 
 static NORETURN void die_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("fatal: ", err, params);
+
 	exit(128);
 }
 
 static void error_builtin(const char *err, va_list params)
 {
+	/*
+	 * We call this trace2 function first and expect it to va_copy 'params'
+	 * before using it (because an 'ap' can only be walked once).
+	 */
+	trace2_cmd_error_va(err, params);
+
 	vreportf("error: ", err, params);
 }