do not write null sha1s to on-disk index

diff --git a/builtin/merge.c b/builtin/merge.c
index 8018a144688541b6ea178e96fe83206209a2902c..5126443fdfe1dc5113943dd3099ab8d87d84887e 100644 (file)
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1109,6 +1109,33 @@ static void write_merge_state(void)
        close(fd);
 }
 
+static int default_edit_option(void)
+{
+       static const char name[] = "GIT_MERGE_AUTOEDIT";
+       const char *e = getenv(name);
+       struct stat st_stdin, st_stdout;
+
+       if (have_message)
+               /* an explicit -m msg without --[no-]edit */
+               return 0;
+
+       if (e) {
+               int v = git_config_maybe_bool(name, e);
+               if (v < 0)
+                       die("Bad value '%s' in environment '%s'", e, name);
+               return v;
+       }
+
+       /* Use editor if stdin and stdout are the same and is a tty */
+       return (!fstat(0, &st_stdin) &&
+               !fstat(1, &st_stdout) &&
+               isatty(0) && isatty(1) &&
+               st_stdin.st_dev == st_stdout.st_dev &&
+               st_stdin.st_ino == st_stdout.st_ino &&
+               st_stdin.st_mode == st_stdout.st_mode);
+}
+
+
 int cmd_merge(int argc, const char **argv, const char *prefix)
 {
        unsigned char result_tree[20];
@@ -1298,7 +1325,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
                    merge_remote_util(commit)->obj &&
                    merge_remote_util(commit)->obj->type == OBJ_TAG) {
                        if (option_edit < 0)
-                               option_edit = 1;
+                               option_edit = default_edit_option();
                        allow_fast_forward = 0;
                }
        }