branch: add a dry_run parameter to create_branch()

Add a dry_run parameter to create_branch() such that dry_run = 1 will
validate a new branch without trying to create it. This will be used in
`git branch --recurse-submodules` to ensure that the new branch can be
created in all submodules.

Signed-off-by: Glen Choo <[email protected]>
Reviewed-by: Jonathan Tan <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: chooglen

branch.c

@@ -423,7 +423,7 @@ static void dwim_branch_start(struct repository *r, const char *start_name,
 void create_branch(struct repository *r,
 		   const char *name, const char *start_name,
 		   int force, int clobber_head_ok, int reflog,
-		   int quiet, enum branch_track track)
+		   int quiet, enum branch_track track, int dry_run)
 {
 	struct object_id oid;
 	char *real_ref;
@@ -445,6 +445,8 @@ void create_branch(struct repository *r,
 	}
 
 	dwim_branch_start(r, start_name, track, &real_ref, &oid);
+	if (dry_run)
+		goto cleanup;
 
 	if (reflog)
 		log_all_ref_updates = LOG_REFS_NORMAL;
@@ -467,6 +469,7 @@ void create_branch(struct repository *r,
 	if (real_ref && track)
 		setup_tracking(ref.buf + 11, real_ref, track, quiet);
 
+cleanup:
 	strbuf_release(&ref);
 	free(real_ref);
 }

branch.h

@@ -62,11 +62,14 @@ void dwim_and_setup_tracking(struct repository *r, const char *new_ref,
  *   - track causes the new branch to be configured to merge the remote branch
  *     that start_name is a tracking branch for (if any).
  *
+ *   - dry_run causes the branch to be validated but not created.
+ *
  */
 void create_branch(struct repository *r,
 		   const char *name, const char *start_name,
 		   int force, int clobber_head_ok,
-		   int reflog, int quiet, enum branch_track track);
+		   int reflog, int quiet, enum branch_track track,
+		   int dry_run);
 
 /*
  * Check if 'name' can be a valid name for a branch; die otherwise.

builtin/branch.c

@@ -859,7 +859,7 @@ int cmd_branch(int argc, const char **argv, const char *prefix)
 
 		create_branch(the_repository,
 			      argv[0], (argc == 2) ? argv[1] : head,
-			      force, 0, reflog, quiet, track);
+			      force, 0, reflog, quiet, track, 0);
 
 	} else
 		usage_with_options(builtin_branch_usage, options);

builtin/checkout.c

@@ -893,7 +893,8 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 				      opts->new_branch_force ? 1 : 0,
 				      opts->new_branch_log,
 				      opts->quiet,
-				      opts->track);
+				      opts->track,
+				      0);
 		new_branch_info->name = opts->new_branch;
 		setup_branch_path(new_branch_info);
 	}