[RFC PATCH] Makefile: create externcheck target

[Denton Liu <liu.denton@gmail.com>]

In b199d7147a (*.[ch]: remove extern from function declarations using
sed, 2019-04-29), we used sed to remove extern from function
definitions. In order to help find and remove future instances of this,
teach Makefile the `externcheck` target which runs the sed script
included in that commit on all applicable source files.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
---

Notes:
    I run this target periodically to ensure that no new instances of extern
    function definitions are introduced. Is this something that we want to
    consider adding for real?

 Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index 5311b1d2c4..791faa24cf 100644
--- a/Makefile
+++ b/Makefile
@@ -2885,6 +2885,9 @@ COCCI_SOURCES = $(filter-out $(THIRD_PARTY_SOURCES),$(FOUND_C_SOURCES))
 	fi
 coccicheck: $(addsuffix .patch,$(filter-out %.pending.cocci,$(wildcard contrib/coccinelle/*.cocci)))
 
+externcheck: $(filter-out $(THIRD_PARTY_SOURCES),$(filter %.c %.h,$(shell $(FIND_SOURCE_FILES))))
+	sed -i 's/^\(\s*\)extern \([^(]*([^*]\)/\1\2/' $^
+
 # See contrib/coccinelle/README
 coccicheck-pending: $(addsuffix .patch,$(wildcard contrib/coccinelle/*.pending.cocci))
 
-- 
2.29.0.rc0.261.g7178c9af9c