diff-index: enable recursive pathspec matching in unpack_trees

The pathspec structure has a few bits of data to drive various operation
modes after we unified the pathspec matching logic in various codepaths.
For example, max_depth field is there so that "git grep" can limit the
output for files found in limited depth of tree traversal. Also in order
to show just the surface level differences in "git diff-tree", recursive
field stops us from descending into deeper level of the tree structure
when it is set to false, and this also affects pathspec matching when
we have wildcards in the pathspec.

The diff-index has always wanted the recursive behaviour, and wanted to
match pathspecs without any depth limit. But we forgot to do so when we
updated tree_entry_interesting() logic to unify the pathspec matching
logic.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -469,6 +469,8 @@ static int diff_cache(struct rev_info *revs,
 	opts.src_index = &the_index;
 	opts.dst_index = NULL;
 	opts.pathspec = &revs->diffopt.pathspec;
+	opts.pathspec->recursive = 1;
+	opts.pathspec->max_depth = -1;
 
 	init_tree_desc(&t, tree->buffer, tree->size);
 	return unpack_trees(1, &t, &opts);

t/t4010-diff-pathspec.sh

@@ -47,6 +47,14 @@ test_expect_success \
     'git diff-index --cached $tree -- path1/ >current &&
      compare_diff_raw current expected'
 
+cat >expected <<\EOF
+:100644 100644 766498d93a4b06057a8e49d23f4068f1170ff38f 0a41e115ab61be0328a19b29f18cdcb49338d516 M	path1/file1
+EOF
+test_expect_success \
+    '"*file1" should show path1/file1' \
+    'git diff-index --cached $tree -- "*file1" >current &&
+     compare_diff_raw current expected'
+
 cat >expected <<\EOF
 :100644 100644 766498d93a4b06057a8e49d23f4068f1170ff38f 0a41e115ab61be0328a19b29f18cdcb49338d516 M	file0
 EOF