git-gui: Guess our share/git-gui/lib path at runtime if possible

Johannes Sixt asked me to try to avoid embedding the runtime location
of git-gui's library directory in the executable script.  Not embedding
it helps the MinGW to be relocatable to another directory should a user
wish to install the programs in a directory other than the location the
packager wanted them to be installed into.

Most of this is a hack.  We try to determine if the path of our master
git-gui script will be able to locate the lib by ../share/git-gui/lib.
This should be true if $(gitexecdir) and $(libdir) have the same prefix.
If they do then we defer the assignment of $(libdir) until runtime, and
we get it from $argv0 rather than embedding it into the script itself.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Makefile

@@ -22,7 +22,7 @@ ifndef gitexecdir
 endif
 
 ifndef sharedir
-	sharedir := $(dir $(gitexecdir))/share
+	sharedir := $(dir $(gitexecdir))share
 endif
 
 ifndef INSTALL
@@ -53,12 +53,19 @@ TCLTK_PATH_SQ = $(subst ','\'',$(TCLTK_PATH))
 libdir   ?= $(sharedir)/git-gui/lib
 libdir_SQ = $(subst ','\'',$(libdir))
 
+exedir    = $(dir $(gitexecdir))share/git-gui/lib
+exedir_SQ = $(subst ','\'',$(exedir))
+
 $(patsubst %.sh,%,$(SCRIPT_SH)) : % : %.sh
 	$(QUIET_GEN)rm -f $@ $@+ && \
+	if test '$(exedir_SQ)' = '$(libdir_SQ)'; then \
+		GITGUI_RELATIVE=1; \
+	fi && \
 	sed -e '1s|#!.*/sh|#!$(SHELL_PATH_SQ)|' \
 		-e 's|^exec wish "$$0"|exec $(subst |,'\|',$(TCLTK_PATH_SQ)) "$$0"|' \
 		-e 's/@@GITGUI_VERSION@@/$(GITGUI_VERSION)/g' \
-		-e 's|@@GITGUI_LIBDIR@@|$(libdir_SQ)|' \
+		-e 's|@@GITGUI_RELATIVE@@|'$$GITGUI_RELATIVE'|' \
+		-e $$GITGUI_RELATIVE's|@@GITGUI_LIBDIR@@|$(libdir_SQ)|' \
 		$@.sh >$@+ && \
 	chmod +x $@+ && \
 	mv $@+ $@
@@ -88,6 +95,7 @@ TRACK_VARS = \
 	$(subst ','\'',SHELL_PATH='$(SHELL_PATH_SQ)') \
 	$(subst ','\'',TCL_PATH='$(TCL_PATH_SQ)') \
 	$(subst ','\'',TCLTK_PATH='$(TCLTK_PATH_SQ)') \
+	$(subst ','\'',gitexecdir='$(gitexecdir_SQ)') \
 	$(subst ','\'',libdir='$(libdir_SQ)') \
 #end TRACK_VARS
 

git-gui.sh

@@ -25,7 +25,11 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA}
 ## configure our library
 
 set oguilib {@@GITGUI_LIBDIR@@}
-if {[string match @@GITGUI_*@@ $oguilib]} {
+set oguirel {@@GITGUI_RELATIVE@@}
+if {$oguirel eq {1}} {
+	set oguilib [file dirname [file dirname [file normalize $argv0]]]
+	set oguilib [file join $oguilib share git-gui lib]
+} elseif {[string match @@* $oguirel]} {
 	set oguilib [file join [file dirname [file normalize $argv0]] lib]
 }
 set idx [file join $oguilib tclIndex]
@@ -55,7 +59,7 @@ if {$idx ne {}} {
 } else {
 	set auto_path [concat [list $oguilib] $auto_path]
 }
-unset -nocomplain fd idx
+unset -nocomplain oguilib oguirel idx fd
 
 if {![catch {set _verbose $env(GITGUI_VERBOSE)}]} {
 	unset _verbose