submodule API: don't handle SM_..{UNSPECIFIED,COMMAND} in to_string()

Change the submodule_strategy_to_string() function added in
3604242f08 (submodule: port init from shell to C, 2016-04-15) to
really return a "const char *". In the "SM_UPDATE_COMMAND" case it
would return a strbuf_detach().

Furthermore, this function would return NULL on SM_UPDATE_UNSPECIFIED,
so it wasn't safe to xstrdup() its return value in the general case,
or to use it in a sprintf() format as the code removed in the
preceding commit did.

But its callers would never call it with either SM_UPDATE_UNSPECIFIED
or SM_UPDATE_COMMAND. Let's have its behavior reflect how its only
user expects it to behave, and BUG() out on the rest.

By doing this we can also stop needlessly xstrdup()-ing and free()-ing
the memory for the config we're setting. We can instead always use
constant strings. We can also use the *_tmp() variant of
git_config_get_string().

Let's also rename this submodule_strategy_to_string() function to
submodule_update_type_to_string(). Now that it's only tasked with
returning a string version of the "enum submodule_update_type type".
Before it would look at the "command" field in "struct
submodule_update_strategy".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Reviewed-by: Glen Choo <chooglen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/submodule--helper.c

@@ -418,7 +418,8 @@ static void init_submodule(const char *path, const char *prefix,
 {
 	const struct submodule *sub;
 	struct strbuf sb = STRBUF_INIT;
-	char *upd = NULL, *url = NULL, *displaypath;
+	const char *upd;
+	char *url = NULL, *displaypath;
 
 	displaypath = get_submodule_displaypath(path, prefix);
 
@@ -474,14 +475,14 @@ static void init_submodule(const char *path, const char *prefix,
 
 	/* Copy "update" setting when it is not set yet */
 	strbuf_addf(&sb, "submodule.%s.update", sub->name);
-	if (git_config_get_string(sb.buf, &upd) &&
+	if (git_config_get_string_tmp(sb.buf, &upd) &&
 	    sub->update_strategy.type != SM_UPDATE_UNSPECIFIED) {
 		if (sub->update_strategy.type == SM_UPDATE_COMMAND) {
 			fprintf(stderr, _("warning: command update mode suggested for submodule '%s'\n"),
 				sub->name);
-			upd = xstrdup("none");
+			upd = "none";
 		} else {
-			upd = xstrdup(submodule_strategy_to_string(&sub->update_strategy));
+			upd = submodule_update_type_to_string(sub->update_strategy.type);
 		}
 
 		if (git_config_set_gently(sb.buf, upd))
@@ -490,7 +491,6 @@ static void init_submodule(const char *path, const char *prefix,
 	strbuf_release(&sb);
 	free(displaypath);
 	free(url);
-	free(upd);
 }
 
 static void init_submodule_cb(const struct cache_entry *list_item, void *cb_data)

submodule.c

@@ -415,10 +415,9 @@ int parse_submodule_update_strategy(const char *value,
 	return 0;
 }
 
-const char *submodule_strategy_to_string(const struct submodule_update_strategy *s)
+const char *submodule_update_type_to_string(enum submodule_update_type type)
 {
-	struct strbuf sb = STRBUF_INIT;
-	switch (s->type) {
+	switch (type) {
 	case SM_UPDATE_CHECKOUT:
 		return "checkout";
 	case SM_UPDATE_MERGE:
@@ -428,12 +427,11 @@ const char *submodule_strategy_to_string(const struct submodule_update_strategy
 	case SM_UPDATE_NONE:
 		return "none";
 	case SM_UPDATE_UNSPECIFIED:
-		return NULL;
 	case SM_UPDATE_COMMAND:
-		strbuf_addf(&sb, "!%s", s->command);
-		return strbuf_detach(&sb, NULL);
+		BUG("init_submodule() should handle type %d", type);
+	default:
+		BUG("unexpected update strategy type: %d", type);
 	}
-	return NULL;
 }
 
 void handle_ignore_submodules_arg(struct diff_options *diffopt,

submodule.h

@@ -72,7 +72,7 @@ void die_path_inside_submodule(struct index_state *istate,
 enum submodule_update_type parse_submodule_update_type(const char *value);
 int parse_submodule_update_strategy(const char *value,
 				    struct submodule_update_strategy *dst);
-const char *submodule_strategy_to_string(const struct submodule_update_strategy *s);
+const char *submodule_update_type_to_string(enum submodule_update_type type);
 void handle_ignore_submodules_arg(struct diff_options *, const char *);
 void show_submodule_diff_summary(struct diff_options *o, const char *path,
 			    struct object_id *one, struct object_id *two,