[PATCH v3 22/23] Makefile: define $(LIB_H) in terms of $(FIND_SOURCE_FILES)

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Combine the definitions of $(FIND_SOURCE_FILES) and $(LIB_H) to speed
up the Makefile, as these are the two main expensive $(shell) commands
that we execute unconditionally.

When see what was in $(FOUND_SOURCE_FILES) that wasn't in $(LIB_H) via
the ad-hoc test of:

    $(error $(filter-out $(LIB_H),$(filter %.h,$(ALL_SOURCE_FILES))))
    $(error $(filter-out $(ALL_SOURCE_FILES),$(filter %.h,$(LIB_H))))

We'll get, respectively:

    Makefile:850: *** t/helper/test-tool.h.  Stop.
    Makefile:850: *** .  Stop.

I.e. we only had a discrepancy when it came to
t/helper/test-tool.h. In terms of correctness this was broken before,
but now works:

    $ make t/helper/test-tool.hco
        HDR t/helper/test-tool.h

This speeds things up a lot:

    $ git -c hyperfine.hook.setup= hyperfine -L rev HEAD~1,HEAD~0 -s 'make -j8 all NO_TCLTK=Y' 'make NO_TCLTK=Y' --war
    mup 10 -M 10
    Benchmark 1: make NO_TCLTK=Y' in 'HEAD~1
      Time (mean ± σ):      99.5 ms ±   0.5 ms    [User: 83.4 ms, System: 20.7 ms]
      Range (min … max):    98.8 ms … 100.2 ms    10 runs

    Benchmark 2: make NO_TCLTK=Y' in 'HEAD~0
      Time (mean ± σ):      69.4 ms ±   0.5 ms    [User: 58.8 ms, System: 14.2 ms]
      Range (min … max):    68.9 ms …  70.3 ms    10 runs

    Summary
      'make NO_TCLTK=Y' in 'HEAD~0' ran
        1.43 ± 0.01 times faster than 'make NO_TCLTK=Y' in 'HEAD~1'

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Makefile | 54 ++++++++++++++++++++++++++----------------------------
 1 file changed, 26 insertions(+), 28 deletions(-)

diff --git a/Makefile b/Makefile
index bae20eb1b40..1041efb6e5e 100644
--- a/Makefile
+++ b/Makefile
@@ -821,12 +821,33 @@ GENERATED_H += hook-list.h
 .PHONY: generated-hdrs
 generated-hdrs: $(GENERATED_H)
 
-LIB_H := $(sort $(patsubst ./%,%,$(shell git ls-files '*.h' ':!t/' ':!Documentation/' 2>/dev/null || \
+## Exhaustive lists of our source files, either dynamically generated,
+## or hardcoded.
+SOURCES_CMD = ( \
+	git ls-files \
+		'*.[hcS]' \
+		'*.sh' \
+		':!*[tp][0-9][0-9][0-9][0-9]*' \
+		':!contrib' \
+		2>/dev/null || \
 	$(FIND) . \
-	-name .git -prune -o \
-	-name t -prune -o \
-	-name Documentation -prune -o \
-	-name '*.h' -print)))
+		\( -name .git -type d -prune \) \
+		-o \( -name '[tp][0-9][0-9][0-9][0-9]*' -prune \) \
+		-o \( -name contrib -type d -prune \) \
+		-o \( -name build -type d -prune \) \
+		-o \( -name 'trash*' -type d -prune \) \
+		-o \( -name '*.[hcS]' -type f -print \) \
+		-o \( -name '*.sh' -type f -print \) \
+		| sed -e 's|^\./||' \
+	)
+FOUND_SOURCE_FILES := $(shell $(SOURCES_CMD))
+
+FOUND_C_SOURCES = $(filter %.c,$(FOUND_SOURCE_FILES))
+FOUND_H_SOURCES = $(filter %.h,$(FOUND_SOURCE_FILES))
+
+COCCI_SOURCES = $(filter-out $(THIRD_PARTY_SOURCES),$(FOUND_C_SOURCES))
+
+LIB_H = $(FOUND_H_SOURCES)
 
 LIB_OBJS += abspath.o
 LIB_OBJS += add-interactive.o
@@ -2661,26 +2682,6 @@ perl/build/man/man3/Git.3pm: perl/Git.pm
 	$(call mkdir_p_parent_template)
 	$(QUIET_GEN)pod2man $< $@
 
-FIND_SOURCE_FILES = ( \
-	git ls-files \
-		'*.[hcS]' \
-		'*.sh' \
-		':!*[tp][0-9][0-9][0-9][0-9]*' \
-		':!contrib' \
-		2>/dev/null || \
-	$(FIND) . \
-		\( -name .git -type d -prune \) \
-		-o \( -name '[tp][0-9][0-9][0-9][0-9]*' -prune \) \
-		-o \( -name contrib -type d -prune \) \
-		-o \( -name build -type d -prune \) \
-		-o \( -name 'trash*' -type d -prune \) \
-		-o \( -name '*.[hcS]' -type f -print \) \
-		-o \( -name '*.sh' -type f -print \) \
-		| sed -e 's|^\./||' \
-	)
-
-FOUND_SOURCE_FILES = $(shell $(FIND_SOURCE_FILES))
-
 $(ETAGS_TARGET): $(FOUND_SOURCE_FILES)
 	$(QUIET_GEN)$(RM) $@+ && \
 	echo $(FOUND_SOURCE_FILES) | xargs etags -a -o $@+ && \
@@ -2860,9 +2861,6 @@ check: $(GENERATED_H)
 		exit 1; \
 	fi
 
-FOUND_C_SOURCES = $(filter %.c,$(FOUND_SOURCE_FILES))
-COCCI_SOURCES = $(filter-out $(THIRD_PARTY_SOURCES),$(FOUND_C_SOURCES))
-
 %.cocci.patch: %.cocci $(COCCI_SOURCES)
 	$(QUIET_SPATCH) \
 	if test $(SPATCH_BATCH_SIZE) = 0; then \
-- 
2.34.0.795.g1e9501ab396