config: drop git_config_get_string_const()

As evidenced by the leak fixes in the previous commit, the "const" in
git_config_get_string_const() clearly misleads people into thinking that
it does not allocate a copy of the string. We can fix this by renaming
it, but it's easier still to just drop it. Of the four remaining
callers:

  - The one in git_config_parse_expiry() still needs to allocate, since
    that's what its callers expect. We can just use the non-const
    version and cast our pointer. Slightly ugly, but the damage is
    contained in one spot.

  - The two in apply are writing to global "const char *" variables, and
    need to continue allocating. We often mark these as const because we
    assign default string literals to them. But in this case we don't do
    that, so we can just declare them as real "char *" pointers and use
    the non-const version.

  - The call in checkout doesn't actually need a copy; it can just use
    the non-allocating "tmp" version of the function.

The function is also mentioned in the MyFirstContribution document. We
can swap that call out for the non-allocating "tmp" variant, which fits
well in the example given.

We'll drop the "configset" and "repo" variants, as well (which are
unused).

Note that this frees up the "const" name, so we could rename the "tmp"
variant back to that. But let's give some time for topics in flight to
adapt to the new code before doing so (if we do it too soon, the
function semantics will change but the compiler won't alert us).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/MyFirstContribution.txt

@@ -319,14 +319,14 @@ function body:
 ...
 
 	git_config(git_default_config, NULL);
-	if (git_config_get_string_const("user.name", &cfg_name) > 0)
+	if (git_config_get_string_tmp("user.name", &cfg_name) > 0)
 		printf(_("No name is found in config\n"));
 	else
 		printf(_("Your name: %s\n"), cfg_name);
 ----
 
 `git_config()` will grab the configuration from config files known to Git and
-apply standard precedence rules. `git_config_get_string_const()` will look up
+apply standard precedence rules. `git_config_get_string_tmp()` will look up
 a specific key ("user.name") and give you the value. There are a number of
 single-key lookup functions like this one; you can see them all (and more info
 about how to use `git_config()`) in `Documentation/technical/api-config.txt`.

apply.c

@@ -30,8 +30,8 @@ struct gitdiff_data {
 
 static void git_apply_config(void)
 {
-	git_config_get_string_const("apply.whitespace", &apply_default_whitespace);
-	git_config_get_string_const("apply.ignorewhitespace", &apply_default_ignorewhitespace);
+	git_config_get_string("apply.whitespace", &apply_default_whitespace);
+	git_config_get_string("apply.ignorewhitespace", &apply_default_ignorewhitespace);
 	git_config(git_xmerge_config, NULL);
 }
 

cache.h

@@ -921,8 +921,8 @@ extern int assume_unchanged;
 extern int prefer_symlink_refs;
 extern int warn_ambiguous_refs;
 extern int warn_on_object_refname_ambiguity;
-extern const char *apply_default_whitespace;
-extern const char *apply_default_ignorewhitespace;
+extern char *apply_default_whitespace;
+extern char *apply_default_ignorewhitespace;
 extern const char *git_attributes_file;
 extern const char *git_hooks_path;
 extern int zlib_compression_level;

checkout.c

@@ -47,7 +47,7 @@ const char *unique_tracking_name(const char *name, struct object_id *oid,
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!git_config_get_string_const("checkout.defaultremote", &default_remote))
+	if (!git_config_get_string_tmp("checkout.defaultremote", &default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
@@ -55,7 +55,6 @@ const char *unique_tracking_name(const char *name, struct object_id *oid,
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
 	free(cb_data.src_ref);
-	free((char *)default_remote);
 	if (cb_data.num_matches == 1) {
 		free(cb_data.default_dst_ref);
 		free(cb_data.default_dst_oid);

config.c

@@ -2006,20 +2006,15 @@ const struct string_list *git_configset_get_value_multi(struct config_set *cs, c
 	return e ? &e->value_list : NULL;
 }
 
-int git_configset_get_string_const(struct config_set *cs, const char *key, const char **dest)
+int git_configset_get_string(struct config_set *cs, const char *key, char **dest)
 {
 	const char *value;
 	if (!git_configset_get_value(cs, key, &value))
-		return git_config_string(dest, key, value);
+		return git_config_string((const char **)dest, key, value);
 	else
 		return 1;
 }
 
-int git_configset_get_string(struct config_set *cs, const char *key, char **dest)
-{
-	return git_configset_get_string_const(cs, key, (const char **)dest);
-}
-
 int git_configset_get_string_tmp(struct config_set *cs, const char *key,
 				 const char **dest)
 {
@@ -2161,22 +2156,15 @@ const struct string_list *repo_config_get_value_multi(struct repository *repo,
 	return git_configset_get_value_multi(repo->config, key);
 }
 
-int repo_config_get_string_const(struct repository *repo,
-				 const char *key, const char **dest)
-{
-	int ret;
-	git_config_check_init(repo);
-	ret = git_configset_get_string_const(repo->config, key, dest);
-	if (ret < 0)
-		git_die_config(key, NULL);
-	return ret;
-}
-
 int repo_config_get_string(struct repository *repo,
 			   const char *key, char **dest)
 {
+	int ret;
 	git_config_check_init(repo);
-	return repo_config_get_string_const(repo, key, (const char **)dest);
+	ret = git_configset_get_string(repo->config, key, dest);
+	if (ret < 0)
+		git_die_config(key, NULL);
+	return ret;
 }
 
 int repo_config_get_string_tmp(struct repository *repo,
@@ -2257,11 +2245,6 @@ const struct string_list *git_config_get_value_multi(const char *key)
 	return repo_config_get_value_multi(the_repository, key);
 }
 
-int git_config_get_string_const(const char *key, const char **dest)
-{
-	return repo_config_get_string_const(the_repository, key, dest);
-}
-
 int git_config_get_string(const char *key, char **dest)
 {
 	return repo_config_get_string(the_repository, key, dest);
@@ -2304,7 +2287,7 @@ int git_config_get_pathname(const char *key, const char **dest)
 
 int git_config_get_expiry(const char *key, const char **output)
 {
-	int ret = git_config_get_string_const(key, output);
+	int ret = git_config_get_string(key, (char **)output);
 	if (ret)
 		return ret;
 	if (strcmp(*output, "now")) {

config.h

@@ -458,7 +458,6 @@ void git_configset_clear(struct config_set *cs);
  */
 int git_configset_get_value(struct config_set *cs, const char *key, const char **dest);
 
-int git_configset_get_string_const(struct config_set *cs, const char *key, const char **dest);
 int git_configset_get_string(struct config_set *cs, const char *key, char **dest);
 int git_configset_get_string_tmp(struct config_set *cs, const char *key, const char **dest);
 int git_configset_get_int(struct config_set *cs, const char *key, int *dest);
@@ -475,8 +474,6 @@ int repo_config_get_value(struct repository *repo,
 			  const char *key, const char **value);
 const struct string_list *repo_config_get_value_multi(struct repository *repo,
 						      const char *key);
-int repo_config_get_string_const(struct repository *repo,
-				 const char *key, const char **dest);
 int repo_config_get_string(struct repository *repo,
 			   const char *key, char **dest);
 int repo_config_get_string_tmp(struct repository *repo,
@@ -532,16 +529,10 @@ void git_config_clear(void);
  * error message and returns -1. When the configuration variable `key` is
  * not found, returns 1 without touching `dest`.
  */
-int git_config_get_string_const(const char *key, const char **dest);
-
-/**
- * Similar to `git_config_get_string_const`, except that retrieved value
- * copied into the `dest` parameter is a mutable string.
- */
 int git_config_get_string(const char *key, char **dest);
 
 /**
- * Similar to `git_config_get_string_const`, but does not allocate any new
+ * Similar to `git_config_get_string`, but does not allocate any new
  * memory; on success `dest` will point to memory owned by the config
  * machinery, which could be invalidated if it is discarded and reloaded.
  */

environment.c

@@ -35,8 +35,8 @@ int repository_format_precious_objects;
 int repository_format_worktree_config;
 const char *git_commit_encoding;
 const char *git_log_output_encoding;
-const char *apply_default_whitespace;
-const char *apply_default_ignorewhitespace;
+char *apply_default_whitespace;
+char *apply_default_ignorewhitespace;
 const char *git_attributes_file;
 const char *git_hooks_path;
 int zlib_compression_level = Z_BEST_SPEED;