split_cmdline: Allow caller to access error string

This allows the caller to add its own error message to that returned
by split_cmdline.  Thus error output following a failed split_cmdline
can be of the form

fatal: Bad alias.test string: cmdline ends with \

rather than

error: cmdline ends with \
fatal: Bad alias.test string

Signed-off-by: Greg Brockman <gdb@mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

alias.c

@@ -22,6 +22,13 @@ char *alias_lookup(const char *alias)
 	return alias_val;
 }
 
+#define SPLIT_CMDLINE_BAD_ENDING 1
+#define SPLIT_CMDLINE_UNCLOSED_QUOTE 2
+static const char *split_cmdline_errors[] = {
+	"cmdline ends with \\",
+	"unclosed quote"
+};
+
 int split_cmdline(char *cmdline, const char ***argv)
 {
 	int src, dst, count = 0, size = 16;
@@ -53,7 +60,7 @@ int split_cmdline(char *cmdline, const char ***argv)
 				if (!c) {
 					free(*argv);
 					*argv = NULL;
-					return error("cmdline ends with \\");
+					return -SPLIT_CMDLINE_BAD_ENDING;
 				}
 			}
 			cmdline[dst++] = c;
@@ -66,7 +73,7 @@ int split_cmdline(char *cmdline, const char ***argv)
 	if (quoted) {
 		free(*argv);
 		*argv = NULL;
-		return error("unclosed quote");
+		return -SPLIT_CMDLINE_UNCLOSED_QUOTE;
 	}
 
 	ALLOC_GROW(*argv, count+1, size);
@@ -75,3 +82,6 @@ int split_cmdline(char *cmdline, const char ***argv)
 	return count;
 }
 
+const char *split_cmdline_strerror(int split_cmdline_errno) {
+	return split_cmdline_errors[-split_cmdline_errno-1];
+}

builtin/merge.c

@@ -486,7 +486,8 @@ static int git_merge_config(const char *k, const char *v, void *cb)
 		buf = xstrdup(v);
 		argc = split_cmdline(buf, &argv);
 		if (argc < 0)
-			die("Bad branch.%s.mergeoptions string", branch);
+			die("Bad branch.%s.mergeoptions string: %s", branch,
+			    split_cmdline_strerror(argc));
 		argv = xrealloc(argv, sizeof(*argv) * (argc + 2));
 		memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 		argc++;

cache.h

@@ -1096,6 +1096,8 @@ void overlay_tree_on_cache(const char *tree_name, const char *prefix);
 
 char *alias_lookup(const char *alias);
 int split_cmdline(char *cmdline, const char ***argv);
+/* Takes a negative value returned by split_cmdline */
+const char *split_cmdline_strerror(int cmdline_errno);
 
 /* builtin/merge.c */
 int checkout_fast_forward(const unsigned char *from, const unsigned char *to);

git.c

@@ -188,7 +188,8 @@ static int handle_alias(int *argcp, const char ***argv)
 		}
 		count = split_cmdline(alias_string, &new_argv);
 		if (count < 0)
-			die("Bad alias.%s string", alias_command);
+			die("Bad alias.%s string: %s", alias_command,
+			    split_cmdline_strerror(count));
 		option_count = handle_options(&new_argv, &count, &envchanged);
 		if (envchanged)
 			die("alias '%s' changes environment variables\n"