tree_entry_interesting: a pathspec only matches at directory boundary

Previously the code did a simple prefix match, which means that a
path in a directory "frotz/" would have matched with pathspec "f".

Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4010-diff-pathspec.sh

@@ -62,4 +62,12 @@ test_expect_success \
     'git diff-index --cached $tree -- file0/ >current &&
      compare_diff_raw current expected'
 
+test_expect_success 'diff-tree pathspec' '
+	tree2=$(git write-tree) &&
+	echo "$tree2" &&
+	git diff-tree -r --name-only $tree $tree2 -- pa path1/a >current &&
+	>expected &&
+	test_cmp expected current
+'
+
 test_done

tree-diff.c

@@ -118,10 +118,16 @@ static int tree_entry_interesting(struct tree_desc *desc, const char *base, int
 				continue;
 
 			/*
-			 * The base is a subdirectory of a path which
-			 * was specified, so all of them are interesting.
+			 * If the base is a subdirectory of a path which
+			 * was specified, all of them are interesting.
 			 */
-			return 2;
+			if (!matchlen ||
+			    base[matchlen] == '/' ||
+			    match[matchlen - 1] == '/')
+				return 2;
+
+			/* Just a random prefix match */
+			continue;
 		}
 
 		/* Does the base match? */