tree-walk.c: don't match submodule entries for 'submod/anything'

Submodules should be handled the same as regular directories with
respect to the presence of a trailing slash, i.e. commands like:

  git diff rev1 rev2 -- $path
  git rev-list HEAD -- $path

should produce the same output whether $path is 'submod' or 'submod/'.
This has been fixed in commit 74b4f7f277 (tree-walk.c: ignore trailing
slash on submodule in tree_entry_interesting(), 2014-01-23).

Unfortunately, that commit had the unintended side effect to handle
'submod/anything' the same as 'submod' and 'submod/' as well, e.g.:

  $ git log --oneline --name-only -- sha1collisiondetection/whatever
  4125f78222 sha1dc: update from upstream
  sha1collisiondetection
  07a20f569b Makefile: fix unaligned loads in sha1dc with UBSan
  sha1collisiondetection
  23e37f8e9d sha1dc: update from upstream
  sha1collisiondetection
  86cfd61e6b sha1dc: optionally use sha1collisiondetection as a submodule
  sha1collisiondetection

Fix this by rejecting submodules as partial pathnames when their
trailing slash is followed by anything.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4010-diff-pathspec.sh

@@ -125,7 +125,9 @@ test_expect_success 'setup submodules' '
 test_expect_success 'diff-tree ignores trailing slash on submodule path' '
 	git diff --name-only HEAD^ HEAD submod >expect &&
 	git diff --name-only HEAD^ HEAD submod/ >actual &&
-	test_cmp expect actual
+	test_cmp expect actual &&
+	git diff --name-only HEAD^ HEAD -- submod/whatever >actual &&
+	test_must_be_empty actual
 '
 
 test_expect_success 'diff multiple wildcard pathspecs' '

tree-walk.c

@@ -851,7 +851,14 @@ static int match_entry(const struct pathspec_item *item,
 	if (matchlen > pathlen) {
 		if (match[pathlen] != '/')
 			return 0;
-		if (!S_ISDIR(entry->mode) && !S_ISGITLINK(entry->mode))
+		/*
+		 * Reject non-directories as partial pathnames, except
+		 * when match is a submodule with a trailing slash and
+		 * nothing else (to handle 'submod/' and 'submod'
+		 * uniformly).
+		 */
+		if (!S_ISDIR(entry->mode) &&
+		    (!S_ISGITLINK(entry->mode) || matchlen > pathlen + 1))
 			return 0;
 	}