[gdm] Make Xsession installation conditional, and off by default

[Jasper St. Pierre <jstpierre src gnome org>]

commit afca46ed9b268b5d19dfc645ddd7a06cca5ae08e
Author: Jasper St. Pierre <jstpierre mecheye net>
Date:   Mon Jun 1 07:55:56 2015 -0700

    Make Xsession installation conditional, and off by default
    
    Most distros use custom logic for their Xsession, so we can't really
    ship a default here. Doing so would break people running "make install"
    and expecting things to work.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=750220

 configure.ac     |    7 +++++++
 data/Makefile.am |   21 +++++++++++++++------
 2 files changed, 22 insertions(+), 6 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index b7e86f8..427f41a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -178,6 +178,12 @@ AC_SUBST(dmconfdir)
 dnl ---------------------------------------------------------------------------
 dnl - Configure arguments
 dnl ---------------------------------------------------------------------------
+AC_ARG_ENABLE(enable-gdm-xsession,
+              AS_HELP_STRING([--enable-gdm-xsession],
+                             [Enable installing the gdm Xsession file @<:@default=no@:>@]),,
+              enable_gdm_xsession=no)
+AM_CONDITIONAL(ENABLE_GDM_XSESSION, test x$enable_gdm_xsession = xyes)
+
 AC_ARG_ENABLE(split-authentication,
              AS_HELP_STRING([--enable-split-authentication],
                              [Enable multiple simultaneous PAM conversations during login 
@<:@default=yes@:>@]),,
@@ -1642,6 +1648,7 @@ echo \
         Build with RBAC:          ${msg_rbac_shutdown}
         Initial VT:               ${GDM_INITIAL_VT}
         Enable documentation:     ${enable_documentation}
+        Install GDM's Xsession:   ${enable_gdm_xsession}
 "
 
 if test x"${use_console_kit}" = x"yes"; then
diff --git a/data/Makefile.am b/data/Makefile.am
index 7d521bb..1bc8d7d 100644
--- a/data/Makefile.am
+++ b/data/Makefile.am
@@ -16,11 +16,6 @@ xauthdir = $(GDM_XAUTH_DIR)
 screenshotdir = $(GDM_SCREENSHOT_DIR)
 cachedir = $(localstatedir)/cache/gdm
 
-Xsession: $(srcdir)/Xsession.in
-       sed     -e 's,[ ]XSESSION_SHELL[@],$(XSESSION_SHELL),g' \
-               -e 's,[ ]libexecdir[@],$(libexecdir),g' \
-               <$(srcdir)/Xsession.in >Xsession
-
 Init: $(srcdir)/Init.in
        sed     -e 's,[ ]X_PATH[@],$(X_PATH),g' \
                <$(srcdir)/Init.in >Init
@@ -195,6 +190,18 @@ CLEANFILES += gdm.service
 
 endif
 
+Xsession_files =
+if ENABLE_GDM_XSESSION
+
+Xsession: $(srcdir)/Xsession.in
+       sed     -e 's,[ ]XSESSION_SHELL[@],$(XSESSION_SHELL),g' \
+               -e 's,[ ]libexecdir[@],$(libexecdir),g' \
+               <$(srcdir)/Xsession.in >Xsession
+Xsession_files += Xsession
+CLEANFILES += Xsession
+
+endif
+
 EXTRA_DIST += gdm.service.in
 
 uninstall-hook:
@@ -218,7 +225,7 @@ uninstall-hook:
        fi
 
 
-install-data-hook: gdm.conf-custom Xsession Init PostSession PreSession $(systemdsystemunit)
+install-data-hook: gdm.conf-custom $(Xsession_files) Init PostSession PreSession $(systemdsystemunit)
        if test '!' -d $(DESTDIR)$(gdmconfdir); then \
                $(mkinstalldirs) $(DESTDIR)$(gdmconfdir); \
                chmod 755 $(DESTDIR)$(gdmconfdir); \
@@ -228,7 +235,9 @@ install-data-hook: gdm.conf-custom Xsession Init PostSession PreSession $(system
                chmod 644 $(DESTDIR)$(GDM_CUSTOM_CONF); \
        fi
 
+if ENABLE_GDM_XSESSION
        $(INSTALL_SCRIPT) Xsession $(DESTDIR)$(gdmconfdir)/Xsession
+endif
 
        if test '!' -d $(DESTDIR)$(initdir); then \
                $(mkinstalldirs) $(DESTDIR)$(initdir); \