diff: teach tree-diff a max-depth parameter

When you are doing a tree-diff, there are basically two options: do not
recurse into subtrees at all, or recurse indefinitely. While most
callers would want to always recurse and see full pathnames, some may
want the efficiency of looking only at a particular level of the tree.
This is currently easy to do for the top-level (just turn off
recursion), but you cannot say "show me what changed in subdir/, but do
not recurse".

This patch adds a max-depth parameter which is measured from the closest
pathspec match, so that you can do:

  git log --raw --max-depth=1 -- a/b/c

and see the raw output for a/b/c/, but not those of a/b/c/d/
(instead of the raw output you would see for a/b/c/d).

Co-authored-by: Toon Claes <toon@iotcl.com>
Signed-off-by: Toon Claes <toon@iotcl.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 116 insertions, 0 deletions

diff --git a/t/t4072-diff-max-depth.sh b/t/t4072-diff-max-depth.sh
new file mode 100755
index 0000000000..0fbf1321f7
--- /dev/null
+++ b/t/t4072-diff-max-depth.sh
@@ -0,0 +1,116 @@
+#!/bin/sh
+
+test_description='check that diff --max-depth will limit recursion'
+. ./test-lib.sh
+
+make_dir() {
+	mkdir -p "$1" &&
+	echo "$2" >"$1/file"
+}
+
+make_files() {
+	echo "$1" >file &&
+	make_dir one "$1" &&
+	make_dir one/two "$1" &&
+	make_dir one/two/three "$1"
+}
+
+test_expect_success 'setup' '
+	git commit --allow-empty -m empty &&
+	git tag empty &&
+	make_files added &&
+	git add . &&
+	git commit -m added &&
+	make_files modified &&
+	git add . &&
+	git commit -m modified &&
+	make_files index &&
+	git add . &&
+	make_files worktree
+'
+
+test_expect_success '--max-depth is disallowed with wildcard pathspecs' '
+	test_must_fail git diff-tree --max-depth=0 HEAD^ HEAD -- "f*"
+'
+
+check_one() {
+	type=$1; shift
+	args=$1; shift
+	path=$1; shift
+	depth=$1; shift
+	test_expect_${expect:-success} "diff-$type $args, path=$path, depth=$depth" "
+		for i in $*; do echo \$i; done >expect &&
+		git diff-$type --max-depth=$depth --name-only $args -- $path >actual &&
+		test_cmp expect actual
+	"
+}
+
+# For tree comparisons, we expect to see subtrees at the boundary
+# get their own entry.
+check_trees() {
+	check_one tree "$*" '' 0 file one
+	check_one tree "$*" '' 1 file one/file one/two
+	check_one tree "$*" '' 2 file one/file one/two/file one/two/three
+	check_one tree "$*" '' 3 file one/file one/two/file one/two/three/file
+	check_one tree "$*" '' -1 file one/file one/two/file one/two/three/file
+	check_one tree "$*" one 0 one
+	check_one tree "$*" one 1 one/file one/two
+	check_one tree "$*" one 2 one/file one/two/file one/two/three
+	check_one tree "$*" one 3 one/file one/two/file one/two/three/file
+	check_one tree "$*" one/two 0 one/two
+	check_one tree "$*" one/two 1 one/two/file one/two/three
+	check_one tree "$*" one/two 2 one/two/file one/two/three/file
+	check_one tree "$*" one/two 2 one/two/file one/two/three/file
+	check_one tree "$*" one/two/three 0 one/two/three
+	check_one tree "$*" one/two/three 1 one/two/three/file
+}
+
+# But for index comparisons, we do not store subtrees at all, so we do not
+# expect them.
+check_index() {
+	check_one "$@" '' 0 file
+	check_one "$@" '' 1 file one/file
+	check_one "$@" '' 2 file one/file one/two/file
+	check_one "$@" '' 3 file one/file one/two/file one/two/three/file
+	check_one "$@" one 0
+	check_one "$@" one 1 one/file
+	check_one "$@" one 2 one/file one/two/file
+	check_one "$@" one 3 one/file one/two/file one/two/three/file
+	check_one "$@" one/two 0
+	check_one "$@" one/two 1 one/two/file
+	check_one "$@" one/two 2 one/two/file one/two/three/file
+	check_one "$@" one/two/three 0
+	check_one "$@" one/two/three 1 one/two/three/file
+
+	# Value '-1' for '--max-depth is the same as recursion without limit,
+	# and thus should always succeed.
+	local expect=
+	check_one "$@" '' -1 file one/file one/two/file one/two/three/file
+}
+
+# Check as a modification...
+check_trees HEAD^ HEAD
+# ...and as an addition...
+check_trees empty HEAD
+# ...and as a deletion.
+check_trees HEAD empty
+
+# We currently only implement max-depth for trees.
+expect=failure
+# Check index against a tree
+check_index index "--cached HEAD"
+# and index against the worktree
+check_index files ""
+expect=
+
+test_expect_success 'find shortest path within embedded pathspecs' '
+	cat >expect <<-\EOF &&
+	one/file
+	one/two/file
+	one/two/three/file
+	EOF
+	git diff-tree --max-depth=2 --name-only HEAD^ HEAD -- one one/two >actual &&
+	test_cmp expect actual
+'
+
+test_done