Add a --dry-run option to git-push.

The default behaviour of git-push is potentially confusing
for new users, since it will push changes that are not on
the current branch. Publishing patches that were still
cooking on a development branch is hard to undo.

It would also be nice to be able to verify the expansion
of refspecs if you've edited them, so that you know
what branches matched on the server.

Adding a --dry-run flag allows the user to experiment
safely and learn how to use git-push properly. Originally
suggested by Steffen Prohaska.

Signed-off-by: Brian Ewins <brian.ewins@gmail.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Documentation/git-push.txt

@@ -9,7 +9,7 @@ git-push - Update remote refs along with associated objects
 SYNOPSIS
 --------
 [verse]
-'git-push' [--all] [--tags] [--receive-pack=<git-receive-pack>]
+'git-push' [--all] [--dry-run] [--tags] [--receive-pack=<git-receive-pack>]
            [--repo=all] [-f | --force] [-v] [<repository> <refspec>...]
 
 DESCRIPTION
@@ -63,6 +63,9 @@ the remote repository.
 	Instead of naming each ref to push, specifies that all
 	refs under `$GIT_DIR/refs/heads/` be pushed.
 
+\--dry-run::
+	Do everything except actually send the updates.
+
 \--tags::
 	All refs under `$GIT_DIR/refs/tags` are pushed, in
 	addition to refspecs explicitly listed on the command

builtin-push.c

@@ -7,9 +7,9 @@
 #include "builtin.h"
 #include "remote.h"
 
-static const char push_usage[] = "git-push [--all] [--tags] [--receive-pack=<git-receive-pack>] [--repo=all] [-f | --force] [-v] [<repository> <refspec>...]";
+static const char push_usage[] = "git-push [--all] [--dry-run] [--tags] [--receive-pack=<git-receive-pack>] [--repo=all] [-f | --force] [-v] [<repository> <refspec>...]";
 
-static int all, force, thin, verbose;
+static int all, dry_run, force, thin, verbose;
 static const char *receivepack;
 
 static const char **refspec;
@@ -69,6 +69,8 @@ static int do_push(const char *repo)
 	argc = 1;
 	if (all)
 		argv[argc++] = "--all";
+	if (dry_run)
+		argv[argc++] = "--dry-run";
 	if (force)
 		argv[argc++] = "--force";
 	if (receivepack)
@@ -147,6 +149,10 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 			all = 1;
 			continue;
 		}
+		if (!strcmp(arg, "--dry-run")) {
+			dry_run = 1;
+			continue;
+		}
 		if (!strcmp(arg, "--tags")) {
 			add_refspec("refs/tags/*");
 			continue;

t/t5516-fetch-push.sh

@@ -244,4 +244,14 @@ test_expect_success 'push with colon-less refspec (4)' '
 
 '
 
+test_expect_success 'push with dry-run' '
+
+	mk_test heads/master &&
+	cd testrepo &&
+	old_commit=$(git show-ref -s --verify refs/heads/master) &&
+	cd .. &&
+	git push --dry-run testrepo &&
+	check_push_result $old_commit heads/master
+'
+
 test_done