config: really treat missing optional path as not configured

These callers expect that git_config_pathname() that returns 0 is a
signal that the variable they passed has a string they need to act
on.  But with the introduction of ":(optional)path" earlier, that is
no longer the case.  If the path specified by the configuration
variable is missing, their variable will get a NULL in it, and they
need to act on it (often, just refraining from copying it elsewhere).

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/blame.c

@@ -739,6 +739,7 @@ static int git_blame_config(const char *var, const char *value,
 		ret = git_config_pathname(&str, var, value);
 		if (ret)
 			return ret;
+		if (str)
 			string_list_insert(&ignore_revs_file_list, str);
 		free(str);
 		return 0;

builtin/receive-pack.c

@@ -177,6 +177,7 @@ static int receive_pack_config(const char *var, const char *value,
 
 		if (git_config_pathname(&path, var, value))
 			return -1;
+		if (path)
 			strbuf_addf(&fsck_msg_types, "%cskiplist=%s",
 				    fsck_msg_types.len ? ',' : '=', path);
 		free(path);

fetch-pack.c

@@ -1872,6 +1872,7 @@ int fetch_pack_fsck_config(const char *var, const char *value,
 
 		if (git_config_pathname(&path, var, value))
 			return -1;
+		if (path)
 			strbuf_addf(msg_types, "%cskiplist=%s",
 				    msg_types->len ? ',' : '=', path);
 		free(path);

fsck.c

@@ -1351,14 +1351,16 @@ int git_fsck_config(const char *var, const char *value,
 
 	if (strcmp(var, "fsck.skiplist") == 0) {
 		char *path;
-		struct strbuf sb = STRBUF_INIT;
 
 		if (git_config_pathname(&path, var, value))
 			return -1;
+		if (path) {
+			struct strbuf sb = STRBUF_INIT;
 			strbuf_addf(&sb, "skiplist=%s", path);
 			free(path);
 			fsck_set_msg_types(options, sb.buf);
 			strbuf_release(&sb);
+		}
 		return 0;
 	}
 

gpg-interface.c

@@ -794,8 +794,16 @@ static int git_gpg_config(const char *var, const char *value,
 		fmtname = "ssh";
 
 	if (fmtname) {
+		char *program;
+		int status;
+
 		fmt = get_format_by_name(fmtname);
-		return git_config_pathname((char **) &fmt->program, var, value);
+		status = git_config_pathname(&program, var, value);
+		if (status)
+			return status;
+		if (program)
+			fmt->program = program;
+		return status;
 	}
 
 	return 0;

setup.c

@@ -1248,7 +1248,7 @@ static int safe_directory_cb(const char *key, const char *value,
 	} else {
 		char *allowed = NULL;
 
-		if (!git_config_pathname(&allowed, key, value)) {
+		if (!git_config_pathname(&allowed, key, value) && allowed) {
 			char *normalized = NULL;
 
 			/*