branch: add read_branch_desc() helper function

This will be used by various callers that make use of the branch
description throughout the system, so that if we need to update
the implementation the callers do not have to be modified.

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

branch.c

@@ -135,6 +135,37 @@ static int setup_tracking(const char *new_ref, const char *orig_ref,
 	return 0;
 }
 
+struct branch_desc_cb {
+	const char *config_name;
+	const char *value;
+};
+
+static int read_branch_desc_cb(const char *var, const char *value, void *cb)
+{
+	struct branch_desc_cb *desc = cb;
+	if (strcmp(desc->config_name, var))
+		return 0;
+	free((char *)desc->value);
+	return git_config_string(&desc->value, var, value);
+}
+
+int read_branch_desc(struct strbuf *buf, const char *branch_name)
+{
+	struct branch_desc_cb cb;
+	struct strbuf name = STRBUF_INIT;
+	strbuf_addf(&name, "branch.%s.description", branch_name);
+	cb.config_name = name.buf;
+	cb.value = NULL;
+	if (git_config(read_branch_desc_cb, &cb) < 0) {
+		strbuf_release(&name);
+		return -1;
+	}
+	if (cb.value)
+		strbuf_addstr(buf, cb.value);
+	strbuf_release(&name);
+	return 0;
+}
+
 int validate_new_branchname(const char *name, struct strbuf *ref,
 			    int force, int attr_only)
 {

branch.h

@@ -46,4 +46,9 @@ void remove_branch_state(void);
 #define BRANCH_CONFIG_VERBOSE 01
 extern void install_branch_config(int flag, const char *local, const char *origin, const char *remote);
 
+/*
+ * Read branch description
+ */
+extern int read_branch_desc(struct strbuf *, const char *branch_name);
+
 #endif