Merge branch 'ta/config-add-to-empty-or-true-fix' into maint

"git config --add section.var val" used to lose existing
section.var whose value was an empty string.

* ta/config-add-to-empty-or-true-fix:
  config: avoid a funny sentinel value "a^"
  make config --add behave correctly for empty and NULL values

builtin/config.c

@@ -586,7 +586,8 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 		check_argc(argc, 2, 2);
 		value = normalize_value(argv[0], argv[1]);
 		return git_config_set_multivar_in_file(given_config_source.file,
-						       argv[0], value, "^$", 0);
+						       argv[0], value,
+						       CONFIG_REGEX_NONE, 0);
 	}
 	else if (actions == ACTION_REPLACE_ALL) {
 		check_write();

cache.h

@@ -1281,6 +1281,8 @@ extern int update_server_info(int);
 #define CONFIG_INVALID_PATTERN 6
 #define CONFIG_GENERIC_ERROR 7
 
+#define CONFIG_REGEX_NONE ((void *)1)
+
 struct git_config_source {
 	unsigned int use_stdin:1;
 	const char *file;

config.c

@@ -1236,10 +1236,15 @@ static struct {
 
 static int matches(const char *key, const char *value)
 {
-	return !strcmp(key, store.key) &&
-		(store.value_regex == NULL ||
-		 (store.do_not_match ^
-		  !regexec(store.value_regex, value, 0, NULL, 0)));
+	if (strcmp(key, store.key))
+		return 0; /* not ours */
+	if (!store.value_regex)
+		return 1; /* always matches */
+	if (store.value_regex == CONFIG_REGEX_NONE)
+		return 0; /* never matches */
+
+	return store.do_not_match ^
+		(value && !regexec(store.value_regex, value, 0, NULL, 0));
 }
 
 static int store_aux(const char *key, const char *value, void *cb)
@@ -1501,6 +1506,8 @@ int git_config_parse_key(const char *key, char **store_key, int *baselen_)
 /*
  * If value==NULL, unset in (remove from) config,
  * if value_regex!=NULL, disregard key/value pairs where value does not match.
+ * if value_regex==CONFIG_REGEX_NONE, do not match any existing values
+ *     (only add a new one)
  * if multi_replace==0, nothing, or only one matching key/value is replaced,
  *     else all matching key/values (regardless how many) are removed,
  *     before the new pair is written.
@@ -1584,6 +1591,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 
 		if (value_regex == NULL)
 			store.value_regex = NULL;
+		else if (value_regex == CONFIG_REGEX_NONE)
+			store.value_regex = CONFIG_REGEX_NONE;
 		else {
 			if (value_regex[0] == '!') {
 				store.do_not_match = 1;
@@ -1615,7 +1624,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 		if (git_config_from_file(store_aux, config_filename, NULL)) {
 			error("invalid config file %s", config_filename);
 			free(store.key);
-			if (store.value_regex != NULL) {
+			if (store.value_regex != NULL &&
+			    store.value_regex != CONFIG_REGEX_NONE) {
 				regfree(store.value_regex);
 				free(store.value_regex);
 			}
@@ -1624,7 +1634,8 @@ int git_config_set_multivar_in_file(const char *config_filename,
 		}
 
 		free(store.key);
-		if (store.value_regex != NULL) {
+		if (store.value_regex != NULL &&
+		    store.value_regex != CONFIG_REGEX_NONE) {
 			regfree(store.value_regex);
 			free(store.value_regex);
 		}

t/t1303-wacky-config.sh

@@ -111,4 +111,24 @@ test_expect_success 'unset many entries' '
 	test_must_fail git config section.key
 '
 
+test_expect_success '--add appends new value after existing empty value' '
+	cat >expect <<-\EOF &&
+
+
+	fool
+	roll
+	EOF
+	cp .git/config .git/config.old &&
+	test_when_finished "mv .git/config.old .git/config" &&
+	cat >.git/config <<-\EOF &&
+	[foo]
+		baz
+		baz =
+		baz = fool
+	EOF
+	git config --add foo.baz roll &&
+	git config --get-all foo.baz >output &&
+	test_cmp expect output
+'
+
 test_done