Add TAGS rule [ci skip]

defs/gmake.mk

@@ -269,6 +269,7 @@ HELP_EXTRA_TASKS = \
 	"  checkout-github:       checkout GitHub Pull Request [PR=1234]" \
 	"  pull-github:           rebase GitHub Pull Request to new worktree [PR=1234]" \
 	"  update-github:         merge master branch and push it to Pull Request [PR=1234]" \
+	"  tags:                  generate TAGS file" \
 	""
 
 # 1. squeeze spaces
@@ -505,3 +506,6 @@ matz: up
 	-e "s/^\(#define RUBY_ABI_VERSION\) .*/\1 0/" \
 	 $(files:%=$(srcdir)/%)
 	$(GIT) -C $(srcdir) commit -m "$(message)" $(files)
+
+tags:
+	$(MAKE) GIT="$(GIT)" -C "$(srcdir)" -f defs/tags.mk

defs/tags.mk

@@ -0,0 +1,18 @@
+# -*- mode: makefile-gmake; indent-tabs-mode: t -*-
+
+SRCS := $(shell $(GIT) ls-files \
+	*.[chy] *.def *.inc *.rb \
+	ccan/ coroutine/ include/ internal/ missing/ \
+	'enc/**/*.[ch]' 'win32/**/*.[ch]' \
+	)
+
+TAGS: $(SRCS)
+	@echo updating $@
+	@tmp=$$(mktemp); \
+	trap 'rm -f "$$tmp"' 0; \
+	{ \
+	  $(GIT) grep -h --no-line-number -o '^ *# *define  *RBIMPL_ATTR_[A-Z_]*(*' -- include | \
+	    sed 's/^ *# *define *//;/_H$$/d;y/(/+/' | sort -u && \
+	  echo 'NORETURN+'; \
+	} > "$$tmp" && \
+	ctags -e -I@"$$tmp" -h .def.inc --langmap=c:+.y.def.inc $(^)