negative-refspec: fix segfault on : refspec

The logic added to check for negative pathspec match by c0192df630
(refspec: add support for negative refspecs, 2020-09-30) looks at
refspec->src assuming it is never NULL, however when
remote.origin.push is set to ":", then refspec->src is NULL,
causing a segfault within strcmp.

Tell git to handle matching refspec by adding the needle to the
set of positively matched refspecs, since matching ":" refspecs
match anything as src.

Add test for matching refspec pushes fetch-negative-refspec
both individually and in combination with a negative refspec.

Signed-off-by: Nipunn Koorapati <nipunn@dropbox.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -755,8 +755,12 @@ static int query_matches_negative_refspec(struct refspec *rs, struct refspec_ite
 
 			if (match_name_with_pattern(key, needle, value, &expn_name))
 				string_list_append_nodup(&reversed, expn_name);
-		} else {
-			if (!strcmp(needle, refspec->src))
+		} else if (refspec->matching) {
+			/* For the special matching refspec, any query should match */
+			string_list_append(&reversed, needle);
+		} else if (!refspec->src) {
+			BUG("refspec->src should not be null here");
+		} else if (!strcmp(needle, refspec->src)) {
 			string_list_append(&reversed, refspec->src);
 		}
 	}

t/t5582-fetch-negative-refspec.sh

@@ -186,4 +186,55 @@ test_expect_success "fetch --prune with negative refspec" '
 	)
 '
 
+test_expect_success "push with matching : and negative refspec" '
+	# Manually handle cleanup, since test_config is not
+	# prepared to take arbitrary options like --add
+	test_when_finished "test_unconfig -C two remote.one.push" &&
+
+	# For convenience, we use "master" to refer to the name of
+	# the branch created by default in the following.
+	#
+	# Repositories two and one have branches other than "master"
+	# but they have no overlap---"master" is the only one that
+	# is shared between them.  And the master branch at two is
+	# behind the master branch at one by one commit.
+	git -C two config --add remote.one.push : &&
+
+	# A matching push tries to update master, fails due to non-ff
+	test_must_fail git -C two push one &&
+
+	# "master" may actually not be "master"---find it out.
+	current=$(git symbolic-ref HEAD) &&
+
+	# If master is in negative refspec, then the command will not attempt
+	# to push and succeed.
+	git -C two config --add remote.one.push "^$current" &&
+
+	# With "master" excluded, this push is a no-op.  Nothing gets
+	# pushed and it succeeds.
+	git -C two push -v one
+'
+
+test_expect_success "push with matching +: and negative refspec" '
+	test_when_finished "test_unconfig -C two remote.one.push" &&
+
+	# The same set-up as above, whose side-effect was a no-op.
+	git -C two config --add remote.one.push +: &&
+
+	# The push refuses to update the "master" branch that is checked
+	# out in the "one" repository, even when it is forced with +:
+	test_must_fail git -C two push one &&
+
+	# "master" may actually not be "master"---find it out.
+	current=$(git symbolic-ref HEAD) &&
+
+	# If master is in negative refspec, then the command will not attempt
+	# to push and succeed
+	git -C two config --add remote.one.push "^$current" &&
+
+	# With "master" excluded, this push is a no-op.  Nothing gets
+	# pushed and it succeeds.
+	git -C two push -v one
+'
+
 test_done