Re: [PATCH 1/1] Makefile: use `git ls-files` to list header files, if possible

[Jeff King <peff@peff.net>]

On Fri, Mar 01, 2019 at 04:54:15PM -0500, Jeff King wrote:

> The one thing we do lose, though, is make's parallelization. It would
> probably be possible to actually shove this into a sub-make which
> defined the hdr-check rules, but I don't know how complicated that would
> become.

This seems to work, though it's kind of horrid.

It costs at least one extra process to run "make hdr-check", and
probably more for things like $(GIT_VERSION) that the Makefile include
likely triggers. But when you're not running hdr-check (which is the
norm), it's zero-cost.

-Peff

diff --git a/Makefile b/Makefile
index c5240942f2..ab6ecf450e 100644
--- a/Makefile
+++ b/Makefile
@@ -2735,16 +2735,8 @@ $(SP_OBJ): %.sp: %.c GIT-CFLAGS FORCE
 .PHONY: sparse $(SP_OBJ)
 sparse: $(SP_OBJ)
 
-GEN_HDRS := command-list.h unicode-width.h
-EXCEPT_HDRS := $(GEN_HDRS) compat% xdiff%
-CHK_HDRS = $(filter-out $(EXCEPT_HDRS),$(patsubst ./%,%,$(LIB_H)))
-HCO = $(patsubst %.h,%.hco,$(CHK_HDRS))
-
-$(HCO): %.hco: %.h FORCE
-	$(QUIET_HDR)$(CC) -include git-compat-util.h -I. -o /dev/null -c -xc $<
-
-.PHONY: hdr-check $(HCO)
-hdr-check: $(HCO)
+hdr-check:
+	$(MAKE) -f hdr-check.mak hdr-check
 
 .PHONY: style
 style:
diff --git a/hdr-check.mak b/hdr-check.mak
new file mode 100644
index 0000000000..b8924afa90
--- /dev/null
+++ b/hdr-check.mak
@@ -0,0 +1,12 @@
+include Makefile
+
+GEN_HDRS := command-list.h unicode-width.h
+EXCEPT_HDRS := $(GEN_HDRS) compat% xdiff%
+CHK_HDRS = $(filter-out $(EXCEPT_HDRS),$(patsubst ./%,%,$(LIB_H)))
+HCO = $(patsubst %.h,%.hco,$(CHK_HDRS))
+
+$(HCO): %.hco: %.h FORCE
+	$(QUIET_HDR)$(CC) -include git-compat-util.h -I. -o /dev/null -c -xc $<
+
+.PHONY: hdr-check $(HCO)
+hdr-check: $(HCO)