[PATCH 04/19] Disallow the empty string as an attribute name

[Michael Haggerty <mhagger@alum.mit.edu>]

Previously, it was possible to have a line like "file.txt =foo" in a
.gitattribute file, after which an invocation like "git check-attr ''
-- file.txt" would succeed.  This patch disallows both constructs.

Please note that any existing .gitattributes file that tries to set an
empty attribute will now trigger the error message "error: : not a
valid attribute name" whereas previously the nonsense was allowed
through.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
---

Currently it is possible to use the empty string as an attribute name.
For example, a .gitattributes file can have a line

    file.txt =foo

and git-check-attr can be invoked as

    git check-attr '' -- file.txt

Indeed, the above command invocation would report that attribute ''
has value 'foo' (though the output looks weird).

I believe this behavior to be a bug, so this patch prohibits the empty
string as an attribute name.  Any attempt to use the empty string as
an attribute name will now trigger the error message "error: : not a
valid attribute name"

Please note that it is conceivable that there are existing
repositories with .gitattributes files that set empty attributes.  If
so, any attempt to read *any* attributes from a file in an affected
directory will fail with the above error message.

 attr.c                |    2 +-
 t/t0003-attributes.sh |    6 ++++++
 2 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/attr.c b/attr.c
index 4a1244f..b1d1d6d 100644
--- a/attr.c
+++ b/attr.c
@@ -53,7 +53,7 @@ static int invalid_attr_name(const char *name, int namelen)
 	 * Attribute name cannot begin with '-' and must consist of
 	 * characters from [-A-Za-z0-9_.].
 	 */
-	if (*name == '-')
+	if (namelen <= 0 || *name == '-')
 		return -1;
 	while (namelen--) {
 		char ch = *name++;
diff --git a/t/t0003-attributes.sh b/t/t0003-attributes.sh
index ebbc755..8c76b79 100755
--- a/t/t0003-attributes.sh
+++ b/t/t0003-attributes.sh
@@ -42,6 +42,12 @@ test_expect_success 'setup' '
 
 '
 
+test_expect_success 'command line checks' '
+
+	test_must_fail git check-attr "" -- f
+
+'
+
 test_expect_success 'attribute test' '
 
 	attr_check f f &&
-- 
1.7.6.8.gd2879