tests: try git apply from subdir of toplevel

Make sure git apply can apply patches with paths relative to the
toplevel of a work tree, a subdirectory, or within the repository
metadata directory.

Relative paths are broken for most commands when run from a
subdirectory of $GIT_DIR, "git apply" being no exception.  The other
tests are meant to keep the demonstration of that company.

Based on a test by Duy.

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

t/t4111-apply-subdir.sh

@@ -0,0 +1,141 @@
+#!/bin/sh
+
+test_description='patching from inconvenient places'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	cat >patch <<-\EOF &&
+	diff file.orig file
+	--- a/file.orig
+	+++ b/file
+	@@ -1 +1,2 @@
+	 1
+	+2
+	EOF
+	patch="$(pwd)/patch" &&
+
+	echo 1 >preimage &&
+	printf "%s\n" 1 2 >postimage &&
+	echo 3 >other &&
+
+	test_tick &&
+	git commit --allow-empty -m basis
+'
+
+test_expect_success 'setup: subdir' '
+	reset_subdir() {
+		git reset &&
+		mkdir -p sub/dir/b &&
+		mkdir -p objects &&
+		cp "$1" file &&
+		cp "$1" objects/file &&
+		cp "$1" sub/dir/file &&
+		cp "$1" sub/dir/b/file &&
+		git add file sub/dir/file sub/dir/b/file objects/file &&
+		cp "$2" file &&
+		cp "$2" sub/dir/file &&
+		cp "$2" sub/dir/b/file &&
+		cp "$2" objects/file
+	}
+'
+
+test_expect_success 'apply from subdir of toplevel' '
+	cp postimage expected &&
+	reset_subdir other preimage &&
+	(
+		cd sub/dir &&
+		git apply "$patch"
+	) &&
+	test_cmp expected sub/dir/file
+'
+
+test_expect_success 'apply --cached from subdir of toplevel' '
+	cp postimage expected &&
+	cp other expected.working &&
+	reset_subdir preimage other &&
+	(
+		cd sub/dir &&
+		git apply --cached "$patch"
+	) &&
+	git show :sub/dir/file >actual &&
+	test_cmp expected actual &&
+	test_cmp expected.working sub/dir/file
+'
+
+test_expect_success 'apply --index from subdir of toplevel' '
+	cp postimage expected &&
+	reset_subdir preimage other &&
+	(
+		cd sub/dir &&
+		test_must_fail git apply --index "$patch"
+	) &&
+	reset_subdir other preimage &&
+	(
+		cd sub/dir &&
+		test_must_fail git apply --index "$patch"
+	) &&
+	reset_subdir preimage preimage &&
+	(
+		cd sub/dir &&
+		git apply --index "$patch"
+	) &&
+	git show :sub/dir/file >actual &&
+	test_cmp expected actual &&
+	test_cmp expected sub/dir/file
+'
+
+test_expect_success 'apply from .git dir' '
+	cp postimage expected &&
+	cp preimage .git/file &&
+	cp preimage .git/objects/file
+	(
+		cd .git &&
+		git apply "$patch"
+	) &&
+	test_cmp expected .git/file
+'
+
+test_expect_failure 'apply from subdir of .git dir' '
+	cp postimage expected &&
+	cp preimage .git/file &&
+	cp preimage .git/objects/file
+	(
+		cd .git/objects &&
+		git apply "$patch"
+	) &&
+	test_cmp expected .git/objects/file
+'
+
+test_expect_success 'apply --cached from .git dir' '
+	cp postimage expected &&
+	cp other expected.working &&
+	cp other .git/file &&
+	reset_subdir preimage other &&
+	(
+		cd .git &&
+		git apply --cached "$patch"
+	) &&
+	git show :file >actual &&
+	test_cmp expected actual &&
+	test_cmp expected.working file &&
+	test_cmp expected.working .git/file
+'
+
+test_expect_success 'apply --cached from subdir of .git dir' '
+	cp postimage expected &&
+	cp preimage expected.subdir &&
+	cp other .git/file &&
+	cp other .git/objects/file &&
+	reset_subdir preimage other &&
+	(
+		cd .git/objects &&
+		git apply --cached "$patch"
+	) &&
+	git show :file >actual &&
+	git show :objects/file >actual.subdir &&
+	test_cmp expected actual &&
+	test_cmp expected.subdir actual.subdir
+'
+
+test_done