Merge branch 'jh/checkout-auto-tracking'

Update "git checkout foo" that DWIMs the intended "upstream" and
turns it into "git checkout -t -b foo remotes/origin/foo" to
correctly take existing remote definitions into account.

The remote "origin" may be what uniquely map its own branch to
remotes/some/where/foo but that some/where may not be "origin".

* jh/checkout-auto-tracking:
  glossary: Update and rephrase the definition of a remote-tracking branch
  branch.c: Validate tracking branches with refspecs instead of refs/remotes/*
  t9114.2: Don't use --track option against "svn-remote"-tracking branches
  t7201.24: Add refspec to keep --track working
  t3200.39: tracking setup should fail if there is no matching refspec.
  checkout: Use remote refspecs when DWIMming tracking branches
  t2024: Show failure to use refspec when DWIMming remote branch names
  t2024: Add tests verifying current DWIM behavior of 'git checkout <branch>'

8 files changed, 221 insertions, 35 deletions

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 23a9413525..ca118ac6bf 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -131,9 +131,9 @@ entries; instead, unmerged entries are ignored.
 	"--track" in linkgit:git-branch[1] for details.
 +
 If no '-b' option is given, the name of the new branch will be
-derived from the remote-tracking branch.  If "remotes/" or "refs/remotes/"
-is prefixed it is stripped away, and then the part up to the
-next slash (which would be the nickname of the remote) is removed.
+derived from the remote-tracking branch, by looking at the local part of
+the refspec configured for the corresponding remote, and then stripping
+the initial part up to the "*".
 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
diff --git a/Documentation/glossary-content.txt b/Documentation/glossary-content.txt
index 68a18e1497..db2a74df93 100644
--- a/Documentation/glossary-content.txt
+++ b/Documentation/glossary-content.txt
@@ -400,12 +400,13 @@ should not be combined with other pathspec.
 	<<def_ref,ref>> and local ref.
 
 [[def_remote_tracking_branch]]remote-tracking branch::
-	A regular Git <<def_branch,branch>> that is used to follow changes from
-	another <<def_repository,repository>>. A remote-tracking
-	branch should not contain direct modifications or have local commits
-	made to it. A remote-tracking branch can usually be
-	identified as the right-hand-side <<def_ref,ref>> in a Pull:
-	<<def_refspec,refspec>>.
+	A <<def_ref,ref>> that is used to follow changes from another
+	<<def_repository,repository>>. It typically looks like
+	'refs/remotes/foo/bar' (indicating that it tracks a branch named
+	'bar' in a remote named 'foo'), and matches the right-hand-side of
+	a configured fetch <<def_refspec,refspec>>. A remote-tracking
+	branch should not contain direct modifications or have local
+	commits made to it.
 
 [[def_repository]]repository::
 	A collection of <<def_ref,refs>> together with an
diff --git a/branch.c b/branch.c
index 97c72bfe70..c5c6984cb5 100644
--- a/branch.c
+++ b/branch.c
@@ -197,6 +197,21 @@ int validate_new_branchname(const char *name, struct strbuf *ref,
 	return 1;
 }
 
+static int check_tracking_branch(struct remote *remote, void *cb_data)
+{
+	char *tracking_branch = cb_data;
+	struct refspec query;
+	memset(&query, 0, sizeof(struct refspec));
+	query.dst = tracking_branch;
+	return !(remote_find_tracking(remote, &query) ||
+		 prefixcmp(query.src, "refs/heads/"));
+}
+
+static int validate_remote_tracking_branch(char *ref)
+{
+	return !for_each_remote(check_tracking_branch, ref);
+}
+
 static const char upstream_not_branch[] =
 N_("Cannot setup tracking information; starting point '%s' is not a branch.");
 static const char upstream_missing[] =
@@ -259,7 +274,7 @@ void create_branch(const char *head,
 	case 1:
 		/* Unique completion -- good, only if it is a real branch */
 		if (prefixcmp(real_ref, "refs/heads/") &&
-		    prefixcmp(real_ref, "refs/remotes/")) {
+		    validate_remote_tracking_branch(real_ref)) {
 			if (explicit_tracking)
 				die(_(upstream_not_branch), start_name);
 			else
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 81b4419da5..f5b50e520f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -825,38 +825,40 @@ static int git_checkout_config(const char *var, const char *value, void *cb)
 }
 
 struct tracking_name_data {
-	const char *name;
-	char *remote;
+	/* const */ char *src_ref;
+	char *dst_ref;
+	unsigned char *dst_sha1;
 	int unique;
 };
 
-static int check_tracking_name(const char *refname, const unsigned char *sha1,
-			       int flags, void *cb_data)
+static int check_tracking_name(struct remote *remote, void *cb_data)
 {
 	struct tracking_name_data *cb = cb_data;
-	const char *slash;
-
-	if (prefixcmp(refname, "refs/remotes/"))
-		return 0;
-	slash = strchr(refname + 13, '/');
-	if (!slash || strcmp(slash + 1, cb->name))
+	struct refspec query;
+	memset(&query, 0, sizeof(struct refspec));
+	query.src = cb->src_ref;
+	if (remote_find_tracking(remote, &query) ||
+	    get_sha1(query.dst, cb->dst_sha1))
 		return 0;
-	if (cb->remote) {
+	if (cb->dst_ref) {
 		cb->unique = 0;
 		return 0;
 	}
-	cb->remote = xstrdup(refname);
+	cb->dst_ref = xstrdup(query.dst);
 	return 0;
 }
 
-static const char *unique_tracking_name(const char *name)
+static const char *unique_tracking_name(const char *name, unsigned char *sha1)
 {
-	struct tracking_name_data cb_data = { NULL, NULL, 1 };
-	cb_data.name = name;
-	for_each_ref(check_tracking_name, &cb_data);
+	struct tracking_name_data cb_data = { NULL, NULL, NULL, 1 };
+	char src_ref[PATH_MAX];
+	snprintf(src_ref, PATH_MAX, "refs/heads/%s", name);
+	cb_data.src_ref = src_ref;
+	cb_data.dst_sha1 = sha1;
+	for_each_remote(check_tracking_name, &cb_data);
 	if (cb_data.unique)
-		return cb_data.remote;
-	free(cb_data.remote);
+		return cb_data.dst_ref;
+	free(cb_data.dst_ref);
 	return NULL;
 }
 
@@ -919,8 +921,8 @@ static int parse_branchname_arg(int argc, const char **argv,
 		if (dwim_new_local_branch_ok &&
 		    !check_filename(NULL, arg) &&
 		    argc == 1) {
-			const char *remote = unique_tracking_name(arg);
-			if (!remote || get_sha1(remote, rev))
+			const char *remote = unique_tracking_name(arg, rev);
+			if (!remote)
 				return argcount;
 			*new_branch = arg;
 			arg = remote;
diff --git a/t/t2024-checkout-dwim.sh b/t/t2024-checkout-dwim.sh
new file mode 100755
index 0000000000..dee55e428f
--- /dev/null
+++ b/t/t2024-checkout-dwim.sh
@@ -0,0 +1,167 @@
+#!/bin/sh
+
+test_description='checkout <branch>
+
+Ensures that checkout on an unborn branch does what the user expects'
+
+. ./test-lib.sh
+
+# Is the current branch "refs/heads/$1"?
+test_branch () {
+	printf "%s\n" "refs/heads/$1" >expect.HEAD &&
+	git symbolic-ref HEAD >actual.HEAD &&
+	test_cmp expect.HEAD actual.HEAD
+}
+
+# Is branch "refs/heads/$1" set to pull from "$2/$3"?
+test_branch_upstream () {
+	printf "%s\n" "$2" "refs/heads/$3" >expect.upstream &&
+	{
+		git config "branch.$1.remote" &&
+		git config "branch.$1.merge"
+	} >actual.upstream &&
+	test_cmp expect.upstream actual.upstream
+}
+
+test_expect_success 'setup' '
+	test_commit my_master &&
+	git init repo_a &&
+	(
+		cd repo_a &&
+		test_commit a_master &&
+		git checkout -b foo &&
+		test_commit a_foo &&
+		git checkout -b bar &&
+		test_commit a_bar
+	) &&
+	git init repo_b &&
+	(
+		cd repo_b &&
+		test_commit b_master &&
+		git checkout -b foo &&
+		test_commit b_foo &&
+		git checkout -b baz &&
+		test_commit b_baz
+	) &&
+	git remote add repo_a repo_a &&
+	git remote add repo_b repo_b &&
+	git config remote.repo_b.fetch \
+		"+refs/heads/*:refs/remotes/other_b/*" &&
+	git fetch --all
+'
+
+test_expect_success 'checkout of non-existing branch fails' '
+	git checkout -B master &&
+	test_might_fail git branch -D xyzzy &&
+
+	test_must_fail git checkout xyzzy &&
+	test_must_fail git rev-parse --verify refs/heads/xyzzy &&
+	test_branch master
+'
+
+test_expect_success 'checkout of branch from multiple remotes fails #1' '
+	git checkout -B master &&
+	test_might_fail git branch -D foo &&
+
+	test_must_fail git checkout foo &&
+	test_must_fail git rev-parse --verify refs/heads/foo &&
+	test_branch master
+'
+
+test_expect_success 'checkout of branch from a single remote succeeds #1' '
+	git checkout -B master &&
+	test_might_fail git branch -D bar &&
+
+	git checkout bar &&
+	test_branch bar &&
+	test_cmp_rev remotes/repo_a/bar HEAD &&
+	test_branch_upstream bar repo_a bar
+'
+
+test_expect_success 'checkout of branch from a single remote succeeds #2' '
+	git checkout -B master &&
+	test_might_fail git branch -D baz &&
+
+	git checkout baz &&
+	test_branch baz &&
+	test_cmp_rev remotes/other_b/baz HEAD &&
+	test_branch_upstream baz repo_b baz
+'
+
+test_expect_success '--no-guess suppresses branch auto-vivification' '
+	git checkout -B master &&
+	test_might_fail git branch -D bar &&
+
+	test_must_fail git checkout --no-guess bar &&
+	test_must_fail git rev-parse --verify refs/heads/bar &&
+	test_branch master
+'
+
+test_expect_success 'setup more remotes with unconventional refspecs' '
+	git checkout -B master &&
+	git init repo_c &&
+	(
+		cd repo_c &&
+		test_commit c_master &&
+		git checkout -b bar &&
+		test_commit c_bar
+		git checkout -b spam &&
+		test_commit c_spam
+	) &&
+	git init repo_d &&
+	(
+		cd repo_d &&
+		test_commit d_master &&
+		git checkout -b baz &&
+		test_commit f_baz
+		git checkout -b eggs &&
+		test_commit c_eggs
+	) &&
+	git remote add repo_c repo_c &&
+	git config remote.repo_c.fetch \
+		"+refs/heads/*:refs/remotes/extra_dir/repo_c/extra_dir/*" &&
+	git remote add repo_d repo_d &&
+	git config remote.repo_d.fetch \
+		"+refs/heads/*:refs/repo_d/*" &&
+	git fetch --all
+'
+
+test_expect_success 'checkout of branch from multiple remotes fails #2' '
+	git checkout -B master &&
+	test_might_fail git branch -D bar &&
+
+	test_must_fail git checkout bar &&
+	test_must_fail git rev-parse --verify refs/heads/bar &&
+	test_branch master
+'
+
+test_expect_success 'checkout of branch from multiple remotes fails #3' '
+	git checkout -B master &&
+	test_might_fail git branch -D baz &&
+
+	test_must_fail git checkout baz &&
+	test_must_fail git rev-parse --verify refs/heads/baz &&
+	test_branch master
+'
+
+test_expect_success 'checkout of branch from a single remote succeeds #3' '
+	git checkout -B master &&
+	test_might_fail git branch -D spam &&
+
+	git checkout spam &&
+	test_branch spam &&
+	test_cmp_rev refs/remotes/extra_dir/repo_c/extra_dir/spam HEAD &&
+	test_branch_upstream spam repo_c spam
+'
+
+test_expect_success 'checkout of branch from a single remote succeeds #4' '
+	git checkout -B master &&
+	test_might_fail git branch -D eggs &&
+
+	git checkout eggs &&
+	test_branch eggs &&
+	test_cmp_rev refs/repo_d/eggs HEAD &&
+	test_branch_upstream eggs repo_d eggs
+'
+
+test_done
diff --git a/t/t3200-branch.sh b/t/t3200-branch.sh
index d969f0ecd8..44ec6a45f4 100755
--- a/t/t3200-branch.sh
+++ b/t/t3200-branch.sh
@@ -317,13 +317,13 @@ test_expect_success 'test tracking setup (non-wildcard, matching)' '
 	test $(git config branch.my4.merge) = refs/heads/master
 '
 
-test_expect_success 'test tracking setup (non-wildcard, not matching)' '
+test_expect_success 'tracking setup fails on non-matching refspec' '
 	git config remote.local.url . &&
 	git config remote.local.fetch refs/heads/s:refs/remotes/local/s &&
 	(git show-ref -q refs/remotes/local/master || git fetch local) &&
-	git branch --track my5 local/master &&
-	! test "$(git config branch.my5.remote)" = local &&
-	! test "$(git config branch.my5.merge)" = refs/heads/master
+	test_must_fail git branch --track my5 local/master &&
+	test_must_fail git config branch.my5.remote &&
+	test_must_fail git config branch.my5.merge
 '
 
 test_expect_success 'test tracking setup via config' '
diff --git a/t/t7201-co.sh b/t/t7201-co.sh
index be9672e5a0..0c9ec0ad44 100755
--- a/t/t7201-co.sh
+++ b/t/t7201-co.sh
@@ -431,6 +431,7 @@ test_expect_success 'detach a symbolic link HEAD' '
 
 test_expect_success \
     'checkout with --track fakes a sensible -b <name>' '
+    git config remote.origin.fetch "+refs/heads/*:refs/remotes/origin/*" &&
     git update-ref refs/remotes/origin/koala/bear renamer &&
 
     git checkout --track origin/koala/bear &&
diff --git a/t/t9114-git-svn-dcommit-merge.sh b/t/t9114-git-svn-dcommit-merge.sh
index 3077851015..f524d2f383 100755
--- a/t/t9114-git-svn-dcommit-merge.sh
+++ b/t/t9114-git-svn-dcommit-merge.sh
@@ -48,7 +48,7 @@ test_expect_success 'setup svn repository' '
 test_expect_success 'setup git mirror and merge' '
 	git svn init "$svnrepo" -t tags -T trunk -b branches &&
 	git svn fetch &&
-	git checkout --track -b svn remotes/trunk &&
+	git checkout -b svn remotes/trunk &&
 	git checkout -b merge &&
 	echo new file > new_file &&
 	git add new_file &&