branch: add 'branch.namePrefix' config param

This patch adds a new configuration parameter for the branch creation
feature: 'branch.namePrefix'. It corresponds to the '--name-prefix'
option of 'git branch' made as configuration parameter, and behaves
exactly like it.

Signed-off-by: VALERI Yoann <yoann.valeri@cea.fr>

Author: valeriyoann

Documentation/config/branch.adoc

@@ -35,6 +35,11 @@ This option defaults to `never`.
 	value of this variable will be used as the default.
 	See linkgit:git-for-each-ref[1] field names for valid values.
 
+`branch.namePrefix`::
+	When a new branch is created with `git branch`, use the provided value as
+	prefix for its name. Can be '@{current}' to use the current branch's name
+	as prefix.
+
 `branch.<name>.remote`::
 	When on branch _<name>_, it tells `git fetch` and `git push`
 	which remote to fetch from or push to.  The remote to push to

branch.c

@@ -368,18 +368,22 @@ int read_branch_desc(struct strbuf *buf, const char *branch_name)
 void add_branch_prefix(const char *name_prefix,
 					   const char *current_branch, struct strbuf *buf)
 {
-	int value = 0;
+	char *config_prefix = NULL;
 
-	if (!name_prefix)
-		return;
+	if (!name_prefix) {
+		if (repo_config_get_string(the_repository, "branch.namePrefix",
+								   &config_prefix))
+			return;
 
-	if (name_prefix[0] != '@') {
-		strbuf_addstr(buf, name_prefix);
-		return;
+		name_prefix = config_prefix;
 	}
 
-	if (strcmp(name_prefix, "@{current}") == 0)
+	if (name_prefix[0] != '@')
+		strbuf_addstr(buf, name_prefix);
+	else if (strcmp(name_prefix, "@{current}") == 0)
 		strbuf_addstr(buf, current_branch);
+
+    free(config_prefix);
 }
 
 /*

t/t3200-branch.sh

@@ -1734,4 +1734,16 @@ test_expect_success 'create branch with --name-prefix' '
 	git branch -D blob-with-prefix-with-prefix
 '
 
+test_expect_success 'create branch with config prefix' '
+	test_config branch.namePrefix blob &&
+	git branch -- -with-prefix &&
+	test_must_fail git branch -- -with-prefix &&
+	test_config branch.namePrefix "@{current}" &&
+	git checkout main &&
+	git branch -- -with-prefix &&
+	test_ref_exists refs/heads/blob-with-prefix &&
+	test_ref_exists refs/heads/main-with-prefix &&
+	git branch -D blob-with-prefix main-with-prefix
+'
+
 test_done