[PATCH v3 2/2] kbuild: make W=1 warn files that are tracked but ignored by git

[Masahiro Yamada <masahiroy@kernel.org>]

The top .gitignore comments about how to detect files breaking
.gitignore rules, but people rarely care about it.

Add a new W=1 warning to detect files that are tracked but ignored by
git. If git is not installed or the source tree is not tracked by git
at all, this script does not print anything.

Running it on v6.2-rc1 detected the following:

  $ make W=1 misc-check
  Documentation/devicetree/bindings/.yamllint: warning: ignored by one of the .gitignore files
  drivers/clk/.kunitconfig: warning: ignored by one of the .gitignore files
  drivers/gpu/drm/tests/.kunitconfig: warning: ignored by one of the .gitignore files
  drivers/hid/.kunitconfig: warning: ignored by one of the .gitignore files
  fs/ext4/.kunitconfig: warning: ignored by one of the .gitignore files
  fs/fat/.kunitconfig: warning: ignored by one of the .gitignore files
  kernel/kcsan/.kunitconfig: warning: ignored by one of the .gitignore files
  lib/kunit/.kunitconfig: warning: ignored by one of the .gitignore files
  mm/kfence/.kunitconfig: warning: ignored by one of the .gitignore files
  tools/testing/selftests/arm64/tags/.gitignore: warning: ignored by one of the .gitignore files
  tools/testing/selftests/arm64/tags/Makefile: warning: ignored by one of the .gitignore files
  tools/testing/selftests/arm64/tags/run_tags_test.sh: warning: ignored by one of the .gitignore files
  tools/testing/selftests/arm64/tags/tags_test.c: warning: ignored by one of the .gitignore files

These are ignored by the '.*' or 'tags' in the top .gitignore, but
there is no rule to negate it.

You might be tempted to do 'git add -f' but I want to have the real
issue fixed (by fixing a .gitignore, or by renaming files, etc.).

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
---

Changes in v3:
  - change working directory to srctree (Nicolas)

Changes in v2:
  - Add $(srctree)/ to make it work with O=

 Makefile           |  6 ++++++
 scripts/misc-check | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100755 scripts/misc-check

diff --git a/Makefile b/Makefile
index acce5ec514f6..c0d7c75d8f14 100644
--- a/Makefile
+++ b/Makefile
@@ -1848,6 +1848,12 @@ rust-analyzer:
 # Misc
 # ---------------------------------------------------------------------------
 
+PHONY += misc-check
+misc-check:
+	$(Q)$(srctree)/scripts/misc-check
+
+all: misc-check
+
 PHONY += scripts_gdb
 scripts_gdb: prepare0
 	$(Q)$(MAKE) $(build)=scripts/gdb
diff --git a/scripts/misc-check b/scripts/misc-check
new file mode 100755
index 000000000000..d40d5484e0c5
--- /dev/null
+++ b/scripts/misc-check
@@ -0,0 +1,19 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+set -e
+
+# Detect files that are tracked but ignored by git. This is checked only when
+# ${KBUILD_EXTRA_WARN} contains 1, git is installed, and the source tree is
+# tracked by git.
+check_tracked_ignored_files () {
+	case "${KBUILD_EXTRA_WARN}" in
+	*1*) ;;
+	*) return;;
+	esac
+
+	git -C ${srctree:-.} ls-files -i -c --exclude-per-directory=.gitignore 2>/dev/null |
+		sed 's/$/: warning: ignored by one of the .gitignore files/' >&2
+}
+
+check_tracked_ignored_files
-- 
2.34.1