Merge branch 'jk/interpret-branch-name' into maint

"git branch @" created refs/heads/@ as a branch, and in general the
code that handled @{-1} and @{upstream} was a bit too loose in
disambiguating.

* jk/interpret-branch-name:
  checkout: restrict @-expansions when finding branch
  strbuf_check_ref_format(): expand only local branches
  branch: restrict @-expansions when deleting
  t3204: test git-branch @-expansion corner cases
  interpret_branch_name: allow callers to restrict expansions
  strbuf_branchname: add docstring
  strbuf_branchname: drop return value
  interpret_branch_name: move docstring to header file
  interpret_branch_name(): handle auto-namelen for @{-1}

10 files changed, 249 insertions, 51 deletions

diff --git a/builtin/branch.c b/builtin/branch.c
index 9d30f55b0b..babfd0f730 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -190,17 +190,20 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 	int ret = 0;
 	int remote_branch = 0;
 	struct strbuf bname = STRBUF_INIT;
+	unsigned allowed_interpret;
 
 	switch (kinds) {
 	case FILTER_REFS_REMOTES:
 		fmt = "refs/remotes/%s";
 		/* For subsequent UI messages */
 		remote_branch = 1;
+		allowed_interpret = INTERPRET_BRANCH_REMOTE;
 
 		force = 1;
 		break;
 	case FILTER_REFS_BRANCHES:
 		fmt = "refs/heads/%s";
+		allowed_interpret = INTERPRET_BRANCH_LOCAL;
 		break;
 	default:
 		die(_("cannot use -a with -d"));
@@ -215,7 +218,7 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 		char *target = NULL;
 		int flags = 0;
 
-		strbuf_branchname(&bname, argv[i]);
+		strbuf_branchname(&bname, argv[i], allowed_interpret);
 		free(name);
 		name = mkpathdup(fmt, bname.buf);
 
diff --git a/builtin/checkout.c b/builtin/checkout.c
index f174f50303..81f07c3ef2 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -452,7 +452,7 @@ static void setup_branch_path(struct branch_info *branch)
 {
 	struct strbuf buf = STRBUF_INIT;
 
-	strbuf_branchname(&buf, branch->name);
+	strbuf_branchname(&buf, branch->name, INTERPRET_BRANCH_LOCAL);
 	if (strcmp(buf.buf, branch->name))
 		branch->name = xstrdup(buf.buf);
 	strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
diff --git a/builtin/merge.c b/builtin/merge.c
index a96d4fb501..848a298556 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -438,7 +438,7 @@ static void merge_name(const char *remote, struct strbuf *msg)
 	char *found_ref;
 	int len, early;
 
-	strbuf_branchname(&bname, remote);
+	strbuf_branchname(&bname, remote, 0);
 	remote = bname.buf;
 
 	memset(branch_head, 0, sizeof(branch_head));
diff --git a/cache.h b/cache.h
index d76d0896bb..b3cf851b59 100644
--- a/cache.h
+++ b/cache.h
@@ -1316,7 +1316,37 @@ extern char *oid_to_hex_r(char *out, const struct object_id *oid);
 extern char *sha1_to_hex(const unsigned char *sha1);	/* static buffer result! */
 extern char *oid_to_hex(const struct object_id *oid);	/* same static buffer as sha1_to_hex */
 
-extern int interpret_branch_name(const char *str, int len, struct strbuf *);
+/*
+ * This reads short-hand syntax that not only evaluates to a commit
+ * object name, but also can act as if the end user spelled the name
+ * of the branch from the command line.
+ *
+ * - "@{-N}" finds the name of the Nth previous branch we were on, and
+ *   places the name of the branch in the given buf and returns the
+ *   number of characters parsed if successful.
+ *
+ * - "<branch>@{upstream}" finds the name of the other ref that
+ *   <branch> is configured to merge with (missing <branch> defaults
+ *   to the current branch), and places the name of the branch in the
+ *   given buf and returns the number of characters parsed if
+ *   successful.
+ *
+ * If the input is not of the accepted format, it returns a negative
+ * number to signal an error.
+ *
+ * If the input was ok but there are not N branch switches in the
+ * reflog, it returns 0.
+ *
+ * If "allowed" is non-zero, it is a treated as a bitfield of allowable
+ * expansions: local branches ("refs/heads/"), remote branches
+ * ("refs/remotes/"), or "HEAD". If no "allowed" bits are set, any expansion is
+ * allowed, even ones to refs outside of those namespaces.
+ */
+#define INTERPRET_BRANCH_LOCAL (1<<0)
+#define INTERPRET_BRANCH_REMOTE (1<<1)
+#define INTERPRET_BRANCH_HEAD (1<<2)
+extern int interpret_branch_name(const char *str, int len, struct strbuf *,
+				 unsigned allowed);
 extern int get_oid_mb(const char *str, struct object_id *oid);
 
 extern int validate_headref(const char *ref);
diff --git a/refs.c b/refs.c
index b9188908b2..2d717742d6 100644
--- a/refs.c
+++ b/refs.c
@@ -404,7 +404,7 @@ int refname_match(const char *abbrev_name, const char *full_name)
 static char *substitute_branch_name(const char **string, int *len)
 {
 	struct strbuf buf = STRBUF_INIT;
-	int ret = interpret_branch_name(*string, *len, &buf);
+	int ret = interpret_branch_name(*string, *len, &buf, 0);
 
 	if (ret == *len) {
 		size_t size;
diff --git a/revision.c b/revision.c
index b37dbec378..771d079f6e 100644
--- a/revision.c
+++ b/revision.c
@@ -147,7 +147,7 @@ static void add_pending_object_with_path(struct rev_info *revs,
 		revs->no_walk = 0;
 	if (revs->reflog_info && obj->type == OBJ_COMMIT) {
 		struct strbuf buf = STRBUF_INIT;
-		int len = interpret_branch_name(name, 0, &buf);
+		int len = interpret_branch_name(name, 0, &buf, 0);
 		int st;
 
 		if (0 < len && name[len] && buf.len)
diff --git a/sha1_name.c b/sha1_name.c
index 73a915ff1b..26ceec1d79 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -1176,7 +1176,8 @@ static int interpret_empty_at(const char *name, int namelen, int len, struct str
 	return 1;
 }
 
-static int reinterpret(const char *name, int namelen, int len, struct strbuf *buf)
+static int reinterpret(const char *name, int namelen, int len,
+		       struct strbuf *buf, unsigned allowed)
 {
 	/* we have extra data, which might need further processing */
 	struct strbuf tmp = STRBUF_INIT;
@@ -1184,7 +1185,7 @@ static int reinterpret(const char *name, int namelen, int len, struct strbuf *bu
 	int ret;
 
 	strbuf_add(buf, name + len, namelen - len);
-	ret = interpret_branch_name(buf->buf, buf->len, &tmp);
+	ret = interpret_branch_name(buf->buf, buf->len, &tmp, allowed);
 	/* that data was not interpreted, remove our cruft */
 	if (ret < 0) {
 		strbuf_setlen(buf, used);
@@ -1205,11 +1206,27 @@ static void set_shortened_ref(struct strbuf *buf, const char *ref)
 	free(s);
 }
 
+static int branch_interpret_allowed(const char *refname, unsigned allowed)
+{
+	if (!allowed)
+		return 1;
+
+	if ((allowed & INTERPRET_BRANCH_LOCAL) &&
+	    starts_with(refname, "refs/heads/"))
+		return 1;
+	if ((allowed & INTERPRET_BRANCH_REMOTE) &&
+	    starts_with(refname, "refs/remotes/"))
+		return 1;
+
+	return 0;
+}
+
 static int interpret_branch_mark(const char *name, int namelen,
 				 int at, struct strbuf *buf,
 				 int (*get_mark)(const char *, int),
 				 const char *(*get_data)(struct branch *,
-							 struct strbuf *))
+							 struct strbuf *),
+				 unsigned allowed)
 {
 	int len;
 	struct branch *branch;
@@ -1234,64 +1251,55 @@ static int interpret_branch_mark(const char *name, int namelen,
 	if (!value)
 		die("%s", err.buf);
 
+	if (!branch_interpret_allowed(value, allowed))
+		return -1;
+
 	set_shortened_ref(buf, value);
 	return len + at;
 }
 
-/*
- * This reads short-hand syntax that not only evaluates to a commit
- * object name, but also can act as if the end user spelled the name
- * of the branch from the command line.
- *
- * - "@{-N}" finds the name of the Nth previous branch we were on, and
- *   places the name of the branch in the given buf and returns the
- *   number of characters parsed if successful.
- *
- * - "<branch>@{upstream}" finds the name of the other ref that
- *   <branch> is configured to merge with (missing <branch> defaults
- *   to the current branch), and places the name of the branch in the
- *   given buf and returns the number of characters parsed if
- *   successful.
- *
- * If the input is not of the accepted format, it returns a negative
- * number to signal an error.
- *
- * If the input was ok but there are not N branch switches in the
- * reflog, it returns 0.
- */
-int interpret_branch_name(const char *name, int namelen, struct strbuf *buf)
+int interpret_branch_name(const char *name, int namelen, struct strbuf *buf,
+			  unsigned allowed)
 {
 	char *at;
 	const char *start;
-	int len = interpret_nth_prior_checkout(name, namelen, buf);
+	int len;
 
 	if (!namelen)
 		namelen = strlen(name);
 
-	if (!len) {
-		return len; /* syntax Ok, not enough switches */
-	} else if (len > 0) {
-		if (len == namelen)
-			return len; /* consumed all */
-		else
-			return reinterpret(name, namelen, len, buf);
+	if (!allowed || (allowed & INTERPRET_BRANCH_LOCAL)) {
+		len = interpret_nth_prior_checkout(name, namelen, buf);
+		if (!len) {
+			return len; /* syntax Ok, not enough switches */
+		} else if (len > 0) {
+			if (len == namelen)
+				return len; /* consumed all */
+			else
+				return reinterpret(name, namelen, len, buf, allowed);
+		}
 	}
 
 	for (start = name;
 	     (at = memchr(start, '@', namelen - (start - name)));
 	     start = at + 1) {
 
-		len = interpret_empty_at(name, namelen, at - name, buf);
-		if (len > 0)
-			return reinterpret(name, namelen, len, buf);
+		if (!allowed || (allowed & INTERPRET_BRANCH_HEAD)) {
+			len = interpret_empty_at(name, namelen, at - name, buf);
+			if (len > 0)
+				return reinterpret(name, namelen, len, buf,
+						   allowed);
+		}
 
 		len = interpret_branch_mark(name, namelen, at - name, buf,
-					    upstream_mark, branch_get_upstream);
+					    upstream_mark, branch_get_upstream,
+					    allowed);
 		if (len > 0)
 			return len;
 
 		len = interpret_branch_mark(name, namelen, at - name, buf,
-					    push_mark, branch_get_push);
+					    push_mark, branch_get_push,
+					    allowed);
 		if (len > 0)
 			return len;
 	}
@@ -1299,22 +1307,19 @@ int interpret_branch_name(const char *name, int namelen, struct strbuf *buf)
 	return -1;
 }
 
-int strbuf_branchname(struct strbuf *sb, const char *name)
+void strbuf_branchname(struct strbuf *sb, const char *name, unsigned allowed)
 {
 	int len = strlen(name);
-	int used = interpret_branch_name(name, len, sb);
+	int used = interpret_branch_name(name, len, sb, allowed);
 
-	if (used == len)
-		return 0;
 	if (used < 0)
 		used = 0;
 	strbuf_add(sb, name + used, len - used);
-	return len;
 }
 
 int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
 {
-	strbuf_branchname(sb, name);
+	strbuf_branchname(sb, name, INTERPRET_BRANCH_LOCAL);
 	if (name[0] == '-')
 		return -1;
 	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
diff --git a/strbuf.h b/strbuf.h
index cf8e4bf532..80047b1bb7 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -574,7 +574,26 @@ static inline void strbuf_complete_line(struct strbuf *sb)
 	strbuf_complete(sb, '\n');
 }
 
-extern int strbuf_branchname(struct strbuf *sb, const char *name);
+/*
+ * Copy "name" to "sb", expanding any special @-marks as handled by
+ * interpret_branch_name(). The result is a non-qualified branch name
+ * (so "foo" or "origin/master" instead of "refs/heads/foo" or
+ * "refs/remotes/origin/master").
+ *
+ * Note that the resulting name may not be a syntactically valid refname.
+ *
+ * If "allowed" is non-zero, restrict the set of allowed expansions. See
+ * interpret_branch_name() for details.
+ */
+extern void strbuf_branchname(struct strbuf *sb, const char *name,
+			      unsigned allowed);
+
+/*
+ * Like strbuf_branchname() above, but confirm that the result is
+ * syntactically valid to be used as a local branch name in refs/heads/.
+ *
+ * The return value is "0" if the result is valid, and "-1" otherwise.
+ */
 extern int strbuf_check_branch_ref(struct strbuf *sb, const char *name);
 
 extern void strbuf_addstr_urlencode(struct strbuf *, const char *,
diff --git a/t/t0100-previous.sh b/t/t0100-previous.sh
index e0a6940232..58c0b7e9b6 100755
--- a/t/t0100-previous.sh
+++ b/t/t0100-previous.sh
@@ -56,5 +56,13 @@ test_expect_success 'merge @{-100} before checking out that many branches yet' '
 	test_must_fail git merge @{-100}
 '
 
+test_expect_success 'log -g @{-1}' '
+	git checkout -b last_branch &&
+	git checkout -b new_branch &&
+	echo "last_branch@{0}" >expect &&
+	git log -g --format=%gd @{-1} >actual &&
+	test_cmp expect actual
+'
+
 test_done
 
diff --git a/t/t3204-branch-name-interpretation.sh b/t/t3204-branch-name-interpretation.sh
new file mode 100755
index 0000000000..698d9cc4f3
--- /dev/null
+++ b/t/t3204-branch-name-interpretation.sh
@@ -0,0 +1,133 @@
+#!/bin/sh
+
+test_description='interpreting exotic branch name arguments
+
+Branch name arguments are usually names which are taken to be inside of
+refs/heads/, but we interpret some magic syntax like @{-1}, @{upstream}, etc.
+This script aims to check the behavior of those corner cases.
+'
+. ./test-lib.sh
+
+expect_branch() {
+	git log -1 --format=%s "$1" >actual &&
+	echo "$2" >expect &&
+	test_cmp expect actual
+}
+
+expect_deleted() {
+	test_must_fail git rev-parse --verify "$1"
+}
+
+test_expect_success 'set up repo' '
+	test_commit one &&
+	test_commit two &&
+	git remote add origin foo.git
+'
+
+test_expect_success 'update branch via @{-1}' '
+	git branch previous one &&
+
+	git checkout previous &&
+	git checkout master &&
+
+	git branch -f @{-1} two &&
+	expect_branch previous two
+'
+
+test_expect_success 'update branch via local @{upstream}' '
+	git branch local one &&
+	git branch --set-upstream-to=local &&
+
+	git branch -f @{upstream} two &&
+	expect_branch local two
+'
+
+test_expect_success 'disallow updating branch via remote @{upstream}' '
+	git update-ref refs/remotes/origin/remote one &&
+	git branch --set-upstream-to=origin/remote &&
+
+	test_must_fail git branch -f @{upstream} two
+'
+
+test_expect_success 'create branch with pseudo-qualified name' '
+	git branch refs/heads/qualified two &&
+	expect_branch refs/heads/refs/heads/qualified two
+'
+
+test_expect_success 'delete branch via @{-1}' '
+	git branch previous-del &&
+
+	git checkout previous-del &&
+	git checkout master &&
+
+	git branch -D @{-1} &&
+	expect_deleted previous-del
+'
+
+test_expect_success 'delete branch via local @{upstream}' '
+	git branch local-del &&
+	git branch --set-upstream-to=local-del &&
+
+	git branch -D @{upstream} &&
+	expect_deleted local-del
+'
+
+test_expect_success 'delete branch via remote @{upstream}' '
+	git update-ref refs/remotes/origin/remote-del two &&
+	git branch --set-upstream-to=origin/remote-del &&
+
+	git branch -r -D @{upstream} &&
+	expect_deleted origin/remote-del
+'
+
+# Note that we create two oddly named local branches here. We want to make
+# sure that we do not accidentally delete either of them, even if
+# shorten_unambiguous_ref() tweaks the name to avoid ambiguity.
+test_expect_success 'delete @{upstream} expansion matches -r option' '
+	git update-ref refs/remotes/origin/remote-del two &&
+	git branch --set-upstream-to=origin/remote-del &&
+	git update-ref refs/heads/origin/remote-del two &&
+	git update-ref refs/heads/remotes/origin/remote-del two &&
+
+	test_must_fail git branch -D @{upstream} &&
+	expect_branch refs/heads/origin/remote-del two &&
+	expect_branch refs/heads/remotes/origin/remote-del two
+'
+
+test_expect_success 'disallow deleting remote branch via @{-1}' '
+	git update-ref refs/remotes/origin/previous one &&
+
+	git checkout -b origin/previous two &&
+	git checkout master &&
+
+	test_must_fail git branch -r -D @{-1} &&
+	expect_branch refs/remotes/origin/previous one &&
+	expect_branch refs/heads/origin/previous two
+'
+
+# The thing we are testing here is that "@" is the real branch refs/heads/@,
+# and not refs/heads/HEAD. These tests should not imply that refs/heads/@ is a
+# sane thing, but it _is_ technically allowed for now. If we disallow it, these
+# can be switched to test_must_fail.
+test_expect_success 'create branch named "@"' '
+	git branch -f @ one &&
+	expect_branch refs/heads/@ one
+'
+
+test_expect_success 'delete branch named "@"' '
+	git update-ref refs/heads/@ two &&
+	git branch -D @ &&
+	expect_deleted refs/heads/@
+'
+
+test_expect_success 'checkout does not treat remote @{upstream} as a branch' '
+	git update-ref refs/remotes/origin/checkout one &&
+	git branch --set-upstream-to=origin/checkout &&
+	git update-ref refs/heads/origin/checkout two &&
+	git update-ref refs/heads/remotes/origin/checkout two &&
+
+	git checkout @{upstream} &&
+	expect_branch HEAD one
+'
+
+test_done