kbuild: warn if FORCE is missing for if_changed(_dep,_rule) and filechk
if_changed, if_changed_dep, and if_changed_rule must have FORCE as a
prerequisite so the command line change is detected.
Documentation/kbuild/makefiles.rst clearly explains it:
Note: It is a typical mistake to forget the FORCE prerequisite.
However, not all people follow the document.
This mistake occurred again and again, so a compelling force is needed.
Show a warning if FORCE is missing in the prerequisite of if_changed
and friends. Same for filechk.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Nicolas Schier <n.schier@avm.de>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index c3c975a..cdec220 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -57,6 +57,7 @@
# - If the content differ the new file is used
# - If they are equal no change, and no timestamp update
define filechk
+ $(check-FORCE)
$(Q)set -e; \
mkdir -p $(dir $@); \
trap "rm -f $(dot-target).tmp" EXIT; \
@@ -130,7 +131,11 @@
# PHONY targets skipped in both cases.
newer-prereqs = $(filter-out $(PHONY),$?)
-if-changed-cond = $(newer-prereqs)$(cmd-check)
+# It is a typical mistake to forget the FORCE prerequisite. Check it here so
+# no more breakage will slip in.
+check-FORCE = $(if $(filter FORCE, $^),,$(warning FORCE prerequisite is missing))
+
+if-changed-cond = $(newer-prereqs)$(cmd-check)$(check-FORCE)
# Execute command if command has changed or prerequisite(s) are updated.
if_changed = $(if $(if-changed-cond), \
