[PATCH 12/13] Makefile: teach scripts to include make variables

From: Jeff King <peff@peff.net>
Date: Feb 5, 2014, 18:05 UTC
Message-ID: <20140205180547.GL15218@sigill.intra.peff.net>
In-Reply-To: <20140205174823.GA15070@sigill.intra.peff.net>

The current scheme for getting build-time variables into a shell script is to munge the script with sed, and stick the munged variable into a special sentinel file so that "make" knows about the dependency.

Instead, we can combine both functions by generating a shell snippet with our value, and then "building" shell scripts by concatenating their snippets. "make" then handles the dependency automatically, and it's easy to generate tighter dependencies.

We demonstrate here by moving the "DIFF" substitution into its own snippet, which lets us rebuild only the single affected file when it changes.

Signed-off-by: Jeff King <peff@peff.net>
---
The astute reader will notice that:

  MAKE_DIFF='diff'
  $MAKE_DIFF ...

that we end up with is not _quite_ the same as replacing "$MAKE_DIFF" in the actual script text with "diff" at build-time. In particular, the way that whitespace and quotes are treated is different. I'm not sure what we would want to do here. Calling "eval" would work. Or we could have the snippet produce a function, rather than a variable, like:

  DIFF() {
      diff "$@"
  }

 Makefile        | 18 +++++++++++++++---
 git-sh-setup.sh |  2 +-
 script/mksh     |  4 ++++
 3 files changed, 20 insertions(+), 4 deletions(-)
 create mode 100644 script/mksh

diff --git a/Makefile b/Makefile
index 203171d..ad3100d 100644
--- a/Makefile
+++ b/Makefile
@@ -1598,6 +1598,11 @@ MAKE/%-string.h: MAKE/% script/mkcstring
 		$(subst -,_,$*) <$< >$@+ && \
 		mv $@+ $@
 
+MAKE/%.sh: MAKE/% script/mksh
+	$(QUIET_GEN)$(SHELL_PATH) script/mksh \
+		$(subst -,_,$*) <$< >$@+ && \
+		mv $@+ $@
+
 LIBS = $(GITLIBS) $(EXTLIBS)
 
 BASIC_CFLAGS += -DSHA1_HEADER=$(call sq,$(SHA1_HEADER)) \
@@ -1734,7 +1739,6 @@ common-cmds.h: $(wildcard Documentation/git-*.txt)
 
 $(eval $(call make-var,SCRIPT-DEFINES,script parameters,\
 	:$(SHELL_PATH)\
-	:$(DIFF)\
 	:$(GIT_VERSION)\
 	:$(localedir)\
 	:$(NO_CURL)\
@@ -1743,18 +1747,24 @@ $(eval $(call make-var,SCRIPT-DEFINES,script parameters,\
 	:$(gitwebdir)\
 	:$(PERL_PATH)\
 ))
+$(eval $(call make-var,DIFF,diff command,$(DIFF)))
 define cmd_munge_script
 $(RM) $@ $@+ && \
+{ \
+includes="$(filter MAKE/%.sh,$^)"; \
+if ! test -z "$$includes"; then \
+	cat $$includes; \
+fi && \
 sed -e '1s|#!.*/sh|#!$(call sqi,$(SHELL_PATH))|' \
     -e 's|@SHELL_PATH@|$(call sqi,$(SHELL_PATH))|' \
-    -e 's|@@DIFF@@|$(call sqi,$(DIFF))|' \
     -e 's|@@LOCALEDIR@@|$(call sqi,$(localedir))|g' \
     -e 's/@@NO_CURL@@/$(NO_CURL)/g' \
     -e 's/@@USE_GETTEXT_SCHEME@@/$(USE_GETTEXT_SCHEME)/g' \
     -e $(BROKEN_PATH_FIX) \
     -e 's|@@GITWEBDIR@@|$(call sqi,$(gitwebdir))|g' \
     -e 's|@@PERL@@|$(call sqi,$(PERL_PATH))|g' \
-    $@.sh >$@+
+    $@.sh; \
+} >$@+
 endef
 
 $(patsubst %.sh,%,$(SCRIPT_SH)) : % : %.sh MAKE/SCRIPT-DEFINES
@@ -1766,6 +1776,8 @@ $(SCRIPT_LIB) : % : %.sh MAKE/SCRIPT-DEFINES
 	$(QUIET_GEN)$(cmd_munge_script) && \
 	mv $@+ $@
 
+git-sh-setup: MAKE/DIFF.sh
+
 git.res: git.rc GIT-VERSION-FILE
 	$(QUIET_RC)$(RC) \
 	  $(join -DMAJOR= -DMINOR=, $(wordlist 1,2,$(subst -, ,$(subst ., ,$(GIT_VERSION))))) \
diff --git a/git-sh-setup.sh b/git-sh-setup.sh
index fffa3c7..627d289 100644
--- a/git-sh-setup.sh
+++ b/git-sh-setup.sh
@@ -285,7 +285,7 @@ clear_local_git_env() {
 # remove lines from $1 that are not in $2, leaving only common lines.
 create_virtual_base() {
 	sz0=$(wc -c <"$1")
-	@@DIFF@@ -u -La/"$1" -Lb/"$1" "$1" "$2" | git apply --no-add
+	$MAKE_DIFF -u -La/"$1" -Lb/"$1" "$1" "$2" | git apply --no-add
 	sz1=$(wc -c <"$1")
 
 	# If we do not have enough common material, it is not
diff --git a/script/mksh b/script/mksh
new file mode 100644
index 0000000..d41e77a
--- /dev/null
+++ b/script/mksh
@@ -0,0 +1,4 @@
+#!/bin/sh
+
+name=$1; shift
+printf "MAKE_%s='%s'\n" "$name" "$(sed "s/'/'\\''/g")"

-- 
1.8.5.2.500.g8060133