git-gui: replace GIT-GUI-VARS with GIT-GUI-BUILD-OPTIONS

The GIT-GUI-VARS file is used to track whether any of our build options
has changed. Unfortunately, the format of that file does not allow us to
propagate those build options to other scripts. But as we are about to
introduce support for the Meson build system, we will extract a couple
of scripts to deduplicate core build logic across Makefiles and Meson.
With this refactoring, it will become necessary to make build options
more widely accessible.

Replace GIT-GUI-VARS with a new GIT-GUI-BUILD-OPTIONS file that is being
populated from a template. This file can easily be sourced from build
scripts in subsequent steps.

Signed-off-by: Patrick Steinhardt <ps@pks.im>

.gitignore

@@ -2,7 +2,7 @@
 config.mak
 Git Gui.app*
 git-gui.tcl
+GIT-GUI-BUILD-OPTIONS
 GIT-VERSION-FILE
-GIT-GUI-VARS
 git-gui
 lib/tclIndex

GIT-GUI-BUILD-OPTIONS.in

@@ -0,0 +1,6 @@
+GITGUI_GITEXECDIR=@GITGUI_GITEXECDIR@
+GITGUI_LIBDIR=@GITGUI_LIBDIR@
+GITGUI_RELATIVE=@GITGUI_RELATIVE@
+SHELL_PATH=@SHELL_PATH@
+TCLTK_PATH=@TCLTK_PATH@
+TCL_PATH=@TCL_PATH@

Makefile

@@ -158,7 +158,7 @@ endif
 ifdef GITGUI_MACOSXAPP
 GITGUI_MAIN := git-gui.tcl
 
-git-gui: GIT-VERSION-FILE GIT-GUI-VARS
+git-gui: GIT-VERSION-FILE GIT-GUI-BUILD-OPTIONS
 	$(QUIET_GEN)rm -f $@ $@+ && \
 	echo '#!$(SHELL_PATH_SQ)' >$@+ && \
 	echo 'if test "z$$*" = zversion ||' >>$@+ && \
@@ -173,7 +173,7 @@ git-gui: GIT-VERSION-FILE GIT-GUI-VARS
 	chmod +x $@+ && \
 	mv $@+ $@
 
-Git\ Gui.app: GIT-VERSION-FILE GIT-GUI-VARS \
+Git\ Gui.app: GIT-VERSION-FILE GIT-GUI-BUILD-OPTIONS \
 		macosx/Info.plist \
 		macosx/git-gui.icns \
 		macosx/AppMain.tcl \
@@ -202,7 +202,7 @@ git-gui: windows/git-gui.sh
 	cp $< $@
 endif
 
-$(GITGUI_MAIN): git-gui.sh GIT-VERSION-FILE GIT-GUI-VARS
+$(GITGUI_MAIN): git-gui.sh GIT-VERSION-FILE GIT-GUI-BUILD-OPTIONS
 	$(QUIET_GEN)rm -f $@ $@+ && \
 	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 		-e 's|@@SHELL_PATH@@|$(SHELL_PATH_SQ)|' \
@@ -238,7 +238,7 @@ update-po:: $(PO_TEMPLATE)
 $(ALL_MSGFILES): %.msg : %.po
 	$(QUIET_MSGFMT0)$(MSGFMT) --statistics --tcl -l $(basename $(notdir $<)) -d $(dir $@) $< $(QUIET_MSGFMT1)
 
-lib/tclIndex: $(ALL_LIBFILES) GIT-GUI-VARS
+lib/tclIndex: $(ALL_LIBFILES) GIT-GUI-BUILD-OPTIONS
 	$(QUIET_INDEX)if echo \
 	  $(foreach p,$(PRELOAD_FILES),source $p\;) \
 	  auto_mkindex lib $(patsubst lib/%,%,$(sort $(ALL_LIBFILES))) \
@@ -252,21 +252,17 @@ lib/tclIndex: $(ALL_LIBFILES) GIT-GUI-VARS
 	 echo >>$@ ; \
 	fi
 
-TRACK_VARS = \
-	$(subst ','\'',SHELL_PATH='$(SHELL_PATH_SQ)') \
-	$(subst ','\'',TCL_PATH='$(TCL_PATH_SQ)') \
-	$(subst ','\'',TCLTK_PATH='$(TCLTK_PATH_SQ)') \
-	$(subst ','\'',gitexecdir='$(gitexecdir_SQ)') \
-	$(subst ','\'',gg_libdir='$(libdir_SQ)') \
-	GITGUI_MACOSXAPP=$(GITGUI_MACOSXAPP) \
-#end TRACK_VARS
-
-GIT-GUI-VARS: FORCE
-	@VARS='$(TRACK_VARS)'; \
-	if test x"$$VARS" != x"`cat $@ 2>/dev/null`" ; then \
-		echo >&2 "    * new locations or Tcl/Tk interpreter"; \
-		echo >$@ "$$VARS"; \
-	fi
+GIT-GUI-BUILD-OPTIONS: FORCE
+	@sed \
+		-e 's|@GITGUI_GITEXECDIR@|$(gitexecdir_SQ)|' \
+		-e 's|@GITGUI_LIBDIR@|$(libdir_SQ)|' \
+		-e 's|@GITGUI_RELATIVE@|$(GITGUI_RELATIVE)|' \
+		-e 's|@SHELL_PATH@|$(SHELL_PATH_SQ)|' \
+		-e 's|@TCLTK_PATH@|$(TCLTK_PATH_SQ)|' \
+		-e 's|@TCL_PATH@|$(TCL_PATH_SQ)|' \
+		$@.in >$@+
+	@if grep -q '^[A-Z][A-Z_]*=@.*@$$' $@+; then echo "Unsubstituted build options in $@" >&2 && exit 1; fi
+	@if cmp $@+ $@ >/dev/null 2>&1; then $(RM) $@+; else mv $@+ $@; fi
 
 ifdef GITGUI_MACOSXAPP
 all:: git-gui Git\ Gui.app
@@ -322,7 +318,7 @@ dist-version:
 
 clean::
 	$(RM_RF) $(GITGUI_MAIN) lib/tclIndex po/*.msg $(PO_TEMPLATE)
-	$(RM_RF) GIT-VERSION-FILE GIT-GUI-VARS
+	$(RM_RF) GIT-VERSION-FILE GIT-GUI-BUILD-OPTIONS
 ifdef GITGUI_MACOSXAPP
 	$(RM_RF) 'Git Gui.app'* git-gui
 endif