Extend "checkout --track" DWIM to support more cases

The code handles additionally "refs/remotes/<something>/name",
"remotes/<something>/name", and "refs/<namespace>/name".

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-checkout.txt

@@ -64,9 +64,16 @@ OPTIONS
 	given. Set it to `always` if you want this behavior when the
 	start-point is either a local or remote branch.
 +
-If no '-b' option was given, a name will be made up for you, by stripping
-the part up to the first slash of the tracked branch.  For example, if you
-called 'git checkout --track origin/next', the branch name will be 'next'.
+If no '-b' option was given, the name of the new branch will be
+derived from the remote branch, by attempting to guess the name
+of the branch on remote system.  If "remotes/" or "refs/remotes/"
+are prefixed, it is stripped away, and then the part up to the
+next slash (which would be the nickname of the remote) is removed.
+This would tell us to use "hack" as the local branch when branching
+off of "origin/hack" (or "remotes/origin/hack", or even
+"refs/remotes/origin/hack").  If the given name has no slash, or the above
+guessing results in an empty name, the guessing is aborted.  You can
+exlicitly give a name with '-b' in such a case.
 
 --no-track::
 	Ignore the branch.autosetupmerge configuration variable.

builtin-checkout.c

@@ -157,7 +157,7 @@ struct checkout_opts {
 	int force;
 	int writeout_error;
 
-	char *new_branch;
+	const char *new_branch;
 	int new_branch_log;
 	enum branch_track track;
 };
@@ -437,27 +437,27 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 
 	git_config(git_default_config, NULL);
 
-	opts.track = -1;
+	opts.track = BRANCH_TRACK_UNSPECIFIED;
 
 	argc = parse_options(argc, argv, options, checkout_usage,
 			     PARSE_OPT_KEEP_DASHDASH);
 
 	/* --track without -b should DWIM */
-	if (opts.track && opts.track != -1 && !opts.new_branch) {
-		char *slash;
-		if (!argc || !strcmp(argv[0], "--"))
+	if (0 < opts.track && !opts.new_branch) {
+		const char *argv0 = argv[0];
+		if (!argc || !strcmp(argv0, "--"))
 			die ("--track needs a branch name");
-		slash = strchr(argv[0], '/');
-		if (slash && !prefixcmp(argv[0], "refs/"))
-			slash = strchr(slash + 1, '/');
-		if (slash && !prefixcmp(argv[0], "remotes/"))
-			slash = strchr(slash + 1, '/');
-		if (!slash || !slash[1])
+		if (!prefixcmp(argv0, "refs/"))
+			argv0 += 5;
+		if (!prefixcmp(argv0, "remotes/"))
+			argv0 += 8;
+		argv0 = strchr(argv0, '/');
+		if (!argv0 || !argv0[1])
 			die ("Missing branch name; try -b");
-		opts.new_branch = slash + 1;
+		opts.new_branch = argv0 + 1;
 	}
 
-	if (opts.track == -1)
+	if (opts.track == BRANCH_TRACK_UNSPECIFIED)
 		opts.track = git_branch_track;
 
 	if (opts.force && opts.merge)

cache.h

@@ -451,6 +451,7 @@ enum safe_crlf {
 extern enum safe_crlf safe_crlf;
 
 enum branch_track {
+	BRANCH_TRACK_UNSPECIFIED = -1,
 	BRANCH_TRACK_NEVER = 0,
 	BRANCH_TRACK_REMOTE,
 	BRANCH_TRACK_ALWAYS,

t/t7201-co.sh

@@ -340,9 +340,30 @@ test_expect_success \
 test_expect_success \
     'checkout with --track fakes a sensible -b <name>' '
     git update-ref refs/remotes/origin/koala/bear renamer &&
+    git update-ref refs/new/koala/bear renamer &&
+
     git checkout --track origin/koala/bear &&
     test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
-    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)"'
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)" &&
+
+    git checkout master && git branch -D koala/bear &&
+
+    git checkout --track refs/remotes/origin/koala/bear &&
+    test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)" &&
+
+    git checkout master && git branch -D koala/bear &&
+
+    git checkout --track remotes/origin/koala/bear &&
+    test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)" &&
+
+    git checkout master && git branch -D koala/bear &&
+
+    git checkout --track refs/new/koala/bear &&
+    test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)"
+'
 
 test_expect_success \
     'checkout with --track, but without -b, fails with too short tracked name' '