t4129: test that git apply warns for unexpected mode changes

There is no test covering what commit 01aff0a (apply: correctly reverse
patch's pre- and post-image mode bits, 2023-12-26) addressed. Prior to
that commit, git apply was erroneously unaware of a file's expected mode
while reverse-patching a file whose mode was not changing.

Add the missing test coverage to assure that git apply is aware of the
expected mode of a file being patched when the patch does not indicate
that the file's mode is changing. This is achieved by arranging a file
mode so that it doesn't agree with patch being applied, and checking git
apply's output for the warning it's supposed to raise in this situation.
Test in both reverse and normal (forward) directions.

Signed-off-by: Mark Mentovai <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: markmentovai

t/t4129-apply-samemode.sh

@@ -102,15 +102,23 @@ test_expect_success POSIXPERM 'do not use core.sharedRepository for working tree
 	)
 '
 
+test_file_mode_staged () {
+	git ls-files --stage -- "$2" >ls-files-output &&
+	test_grep "^$1 " ls-files-output
+}
+
+test_file_mode_HEAD () {
+	git ls-tree HEAD -- "$2" >ls-tree-output &&
+	test_grep "^$1 " ls-tree-output
+}
+
 test_expect_success 'git apply respects core.fileMode' '
 	test_config core.fileMode false &&
 	echo true >script.sh &&
 	git add --chmod=+x script.sh &&
-	git ls-files -s script.sh >ls-files-output &&
-	test_grep "^100755" ls-files-output &&
+	test_file_mode_staged 100755 script.sh &&
 	test_tick && git commit -m "Add script" &&
-	git ls-tree -r HEAD script.sh >ls-tree-output &&
-	test_grep "^100755" ls-tree-output &&
+	test_file_mode_HEAD 100755 script.sh &&
 
 	echo true >>script.sh &&
 	test_tick && git commit -m "Modify script" script.sh &&
@@ -126,7 +134,59 @@ test_expect_success 'git apply respects core.fileMode' '
 	test_grep ! "has type 100644, expected 100755" err &&
 
 	git apply --cached patch 2>err &&
-	test_grep ! "has type 100644, expected 100755" err
+	test_grep ! "has type 100644, expected 100755" err &&
+	git reset --hard
+'
+
+test_expect_success 'setup: git apply [--reverse] warns about incorrect file modes' '
+	test_config core.fileMode false &&
+
+	>mode_test &&
+	git add --chmod=-x mode_test &&
+	test_file_mode_staged 100644 mode_test &&
+	test_tick && git commit -m "add mode_test" &&
+	test_file_mode_HEAD 100644 mode_test &&
+	git tag mode_test_forward_initial &&
+
+	echo content >>mode_test &&
+	test_tick && git commit -m "append to mode_test" mode_test &&
+	test_file_mode_HEAD 100644 mode_test &&
+	git tag mode_test_reverse_initial &&
+
+	git format-patch -1 --stdout >patch &&
+	test_grep "^index .* 100644$" patch
+'
+
+test_expect_success 'git apply warns about incorrect file modes' '
+	test_config core.fileMode false &&
+	git reset --hard mode_test_forward_initial &&
+
+	git add --chmod=+x mode_test &&
+	test_file_mode_staged 100755 mode_test &&
+	test_tick && git commit -m "make mode_test executable" &&
+	test_file_mode_HEAD 100755 mode_test &&
+
+	git apply --index patch 2>err &&
+	test_grep "has type 100755, expected 100644" err &&
+	test_file_mode_staged 100755 mode_test &&
+	test_tick && git commit -m "redo: append to mode_test" &&
+	test_file_mode_HEAD 100755 mode_test
+'
+
+test_expect_success 'git apply --reverse warns about incorrect file modes' '
+	test_config core.fileMode false &&
+	git reset --hard mode_test_reverse_initial &&
+
+	git add --chmod=+x mode_test &&
+	test_file_mode_staged 100755 mode_test &&
+	test_tick && git commit -m "make mode_test executable" &&
+	test_file_mode_HEAD 100755 mode_test &&
+
+	git apply --index --reverse patch 2>err &&
+	test_grep "has type 100755, expected 100644" err &&
+	test_file_mode_staged 100755 mode_test &&
+	test_tick && git commit -m "undo: append to mode_test" &&
+	test_file_mode_HEAD 100755 mode_test
 '
 
 test_expect_success POSIXPERM 'patch mode for new file is canonicalized' '