Actually allow TAG_FIXUP branches in fast-import

Michael Haggerty <mhagger@alum.mit.edu> noticed while debugging a
Git backend for cvs2svn that fast-import was barfing when he tried
to use "TAG_FIXUP" as a branch name for temporary work needed to
cleanup the tree prior to creating an annotated tag object.

The reason we were rejecting the branch name was check_ref_format()
returns -2 when there are less than 2 '/' characters in the input
name.  TAG_FIXUP has 0 '/' characters, but is technically just as
valid of a ref as HEAD and MERGE_HEAD, so we really should permit it
(and any other similar looking name) during import.

New test cases have been added to make sure we still detect very
wrong branch names (e.g. containing [ or starting with .) and yet
still permit reasonable names (e.g. TAG_FIXUP).

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

fast-import.c

@@ -524,8 +524,12 @@ static struct branch *new_branch(const char *name)
 
 	if (b)
 		die("Invalid attempt to create duplicate branch: %s", name);
-	if (check_ref_format(name))
+	switch (check_ref_format(name)) {
+	case  0: break; /* its valid */
+	case -2: break; /* valid, but too few '/', allow anyway */
+	default:
 		die("Branch name doesn't conform to GIT standards: %s", name);
+	}
 
 	b = pool_calloc(1, sizeof(struct branch));
 	b->name = pool_strdup(name);

t/t9300-fast-import.sh

@@ -170,6 +170,53 @@ test_expect_failure \
     'git-fast-import <input'
 rm -f .git/objects/pack_* .git/objects/index_*
 
+cat >input <<INPUT_END
+commit .badbranchname
+committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+data <<COMMIT
+corrupt
+COMMIT
+
+from refs/heads/master
+
+INPUT_END
+test_expect_failure \
+    'B: fail on invalid branch name ".badbranchname"' \
+    'git-fast-import <input'
+rm -f .git/objects/pack_* .git/objects/index_*
+
+cat >input <<INPUT_END
+commit bad[branch]name
+committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+data <<COMMIT
+corrupt
+COMMIT
+
+from refs/heads/master
+
+INPUT_END
+test_expect_failure \
+    'B: fail on invalid branch name "bad[branch]name"' \
+    'git-fast-import <input'
+rm -f .git/objects/pack_* .git/objects/index_*
+
+cat >input <<INPUT_END
+commit TEMP_TAG
+committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+data <<COMMIT
+tag base
+COMMIT
+
+from refs/heads/master
+
+INPUT_END
+test_expect_success \
+    'B: accept branch name "TEMP_TAG"' \
+    'git-fast-import <input &&
+	 test -f .git/TEMP_TAG &&
+	 test `git rev-parse master` = `git rev-parse TEMP_TAG^`'
+rm -f .git/TEMP_TAG
+
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