[PATCH] checkpatch: warn about possible missing gitignore coverage in selftests

[Cihan Karadag <cihan.cihan@gmail.com>]

Per selftests documentation [1], every generated test binary must be
added to gitignore to prevent leaving untracked files in the kernel
tree.

This is an easy mistake to make when adding a new test. In fact, a
search of selftests history turns up dozens of standalone follow-up
patches with titles like "add missing gitignore for <binary>", each
needed only because the original patch adding a new test
didn't also update gitignore.

Add a SELFTESTS_GITIGNORE check that warns about gitignore coverage
whenever a patch adds a new file under tools/testing/selftests/, the
same way FILE_PATH_CHANGES warns about MAINTAINERS on any added,
moved, or deleted file.

The warning fires once per patch via a $reported_selftests_gitignore
guard, even when a patch adds several new files under
tools/testing/selftests/ at once, mirroring
$reported_maintainer_file's per patch dedup for FILE_PATH_CHANGES.

Link: https://docs.kernel.org/dev-tools/kselftest.html#contributing-new-tests-details [1]

Signed-off-by: Cihan Karadag <cihan.cihan@gmail.com>
---
 Documentation/dev-tools/checkpatch.rst |  7 +++++++
 scripts/checkpatch.pl                  | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/Documentation/dev-tools/checkpatch.rst b/Documentation/dev-tools/checkpatch.rst
index 6139a08c34cd8..9201d1cda0d44 100644
--- a/Documentation/dev-tools/checkpatch.rst
+++ b/Documentation/dev-tools/checkpatch.rst
@@ -1293,6 +1293,13 @@ Others
   **PRINTF_0XDECIMAL**
     Prefixing 0x with decimal output is defective and should be corrected.
 
+  **SELFTESTS_GITIGNORE**
+    Warn that, if the new file(s) added under tools/testing/selftests/
+    generate any test objects, those objects need to be added to
+    .gitignore.
+
+    See: https://www.kernel.org/doc/html/latest/dev-tools/kselftest.html
+
   **SPDX_LICENSE_TAG**
     The source file is missing or has an improper SPDX identifier tag.
     The Linux kernel requires the precise SPDX identifier in all source files,
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 2b7a42bbdd94f..a4ead4677e3c6 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -2701,6 +2701,7 @@ sub process {
 	my $commit_log_long_line = 0;
 	my $commit_log_has_diff = 0;
 	my $reported_maintainer_file = 0;
+	my $reported_selftests_gitignore = 0;
 	my $non_utf8_charset = 0;
 
 	my $last_git_commit_id_linenr = -1;
@@ -3492,6 +3493,15 @@ sub process {
 			     "added, moved or deleted file(s), does MAINTAINERS need updating?\n" . $herecurr);
 		}
 
+# Check for new files added under kselftests
+		if (!$reported_selftests_gitignore && !$in_commit_log &&
+		    ($line =~ /^new file mode\s*\d+\s*$/) &&
+		    ($realfile =~ m@^tools/testing/selftests/@)) {
+			$reported_selftests_gitignore = 1;
+			WARN("SELFTESTS_GITIGNORE",
+			     "Added file(s) under tools/testing/selftests/, if they generate any test objects make sure they are added to .gitignore. See: Documentation/dev-tools/kselftest.rst\n");
+		}
+
 # Check for adding new DT bindings not in schema format
 		if (!$in_commit_log &&
 		    ($line =~ /^new file mode\s*\d+\s*$/) &&
-- 
2.54.0