build: Support VPATH builds.

This allows using 'mcron' before it is installed without hardcoding the
local build environment in the executable.

* build-aux/pre-inst-env.in: New script.
* configure.ac (AC_CONFIG_FILES): Create it.
(AC_CONFIG_HEADER): Add 'config.h'.
(moduledir): New variable.
(PACKAGE_LOAD_PATH): new C preprocessor macro.
* mcron.c: Include "config.h".
(main): Don't overwrite Guile load paths.
(inner_main): Prepend Mcron modules load paths.
* Makefile.am (.scm.go, doc/mcron.1): Use 'pre-inst-env'.
(mcron_CFLAGS): Remove GUILE_LOAD_PATH macro.
(noinst_SCRIPTS): New variable.
* .gitignore: Update.

.gitignore

@@ -25,6 +25,8 @@ aclocal.m4
 autom4te.cache
 compile
 config.cache
+config.h
+config.h.in
 config.log
 config.scm
 config.status
@@ -33,4 +35,6 @@ core.scm
 depcomp
 install-sh
 missing
+pre-inst-env
+stamp-h1
 texinfo.tex

Makefile.am

@@ -18,7 +18,7 @@
 
 bin_PROGRAMS = mcron
 mcron_SOURCES = mcron.c
-mcron_CFLAGS = @GUILE_CFLAGS@ -DGUILE_LOAD_PATH=\"$(datadir):./scm:...\"
+mcron_CFLAGS = @GUILE_CFLAGS@
 mcron_DEPENDENCIES = $(GOBJECTS) # Build Guile modules before linking.
 mcron_LDADD = @GUILE_LIBS@
 
@@ -65,13 +65,14 @@ dist_mcronmodule_DATA = 		\
 	$(AM_V_GUILEC)$(MKDIR_P) `dirname "$@"` ;			\
 	unset GUILE_LOAD_COMPILED_PATH ;				\
 	LC_ALL=C							\
-	$(GUILD) compile						\
+	$(top_builddir)/pre-inst-env $(GUILD) compile			\
 	  --load-path="$(top_builddir)/scm"				\
 	  --load-path="$(top_srcdir)/scm"				\
 	  --warn=format --warn=unbound-variable --warn=arity-mismatch	\
 	  --target="$(host)" --output="$@" "$<"
 
 SUFFIXES = .go
+noinst_SCRIPTS = pre-inst-env
 
 dist-hook: gen-ChangeLog
 
@@ -128,7 +129,7 @@ dist_man_MANS = doc/mcron.1
 # elemental man page.  Will only work once the mcron program is installed.
 doc/mcron.1: mcron.c
 	-$(AM_V_HELP2MAN)$(MKDIR_P) `dirname "$@"` ; 			\
-	$(HELP2MAN)							\
+	$(top_builddir)/pre-inst-env $(HELP2MAN)			\
 	  -n 'a program to run tasks at regular (or not) intervals'	\
 	  ./mcron > $@
 

build-aux/pre-inst-env.in

@@ -0,0 +1,35 @@
+#!/bin/sh
+
+# Copyright © 2015, 2016 Mathieu Lirzin <mthl@gnu.org>
+#
+# This file is part of GNU Mcron.
+#
+# GNU Mcron is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# GNU Mcron is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GNU Mcron.  If not, see <http://www.gnu.org/licenses/>.
+
+abs_top_srcdir="`cd "@abs_top_srcdir@" > /dev/null; pwd`"
+abs_top_builddir="`cd "@abs_top_builddir@" > /dev/null; pwd`"
+
+GUILE_LOAD_COMPILED_PATH="$abs_top_builddir/scm${GUILE_LOAD_COMPILED_PATH:+:}$GUILE_LOAD_COMPILED_PATH"
+GUILE_LOAD_PATH="$abs_top_builddir/scm:$abs_top_srcdir/scm${GUILE_LOAD_PATH:+:}:$GUILE_LOAD_PATH"
+export GUILE_LOAD_COMPILED_PATH GUILE_LOAD_PATH
+
+PATH="$abs_top_builddir:$PATH"
+export PATH
+
+# Define $MCRON_UNINSTALLED to prevent 'mcron' from prepending @moduledir@ to
+# the Guile load paths.
+MCRON_UNINSTALLED=1
+export MCRON_UNINSTALLED
+
+exec "$@"

configure.ac

@@ -23,13 +23,15 @@
 
 AC_PREREQ(2.61)
 AC_INIT([GNU Mcron], [1.0.8], [bug-mcron@gnu.org])
+AC_CONFIG_HEADER([config.h])
 AC_CONFIG_AUX_DIR([build-aux])
 AM_INIT_AUTOMAKE([subdir-objects])
 AM_SILENT_RULES([yes])		# enables silent rules by default
 
-mcronmoduledir="${datarootdir}/guile/site/2.0/mcron"
-AC_SUBST([mcronmoduledir])
-
+moduledir="${datarootdir}/guile/site/2.0"
+AC_SUBST([mcronmoduledir], ["${moduledir}/mcron"])
+AC_DEFINE_UNQUOTED([PACKAGE_LOAD_PATH], ["${moduledir}"],
+  [Define to the guile modules location of this package.])
 AC_MSG_CHECKING([whether debugging is requested])
 AC_ARG_ENABLE(debug,
               AC_HELP_STRING([--enable-debug],
@@ -181,6 +183,8 @@ AC_SUBST(CONFIG_TMP_DIR)
 real_program_prefix=`echo $program_prefix | sed s/NONE//`
 AC_SUBST(real_program_prefix)
 
+AC_CONFIG_FILES([pre-inst-env:build-aux/pre-inst-env.in],
+  [chmod +x pre-inst-env])
 AC_CONFIG_FILES([doc/config.texi
                  Makefile
                  scm/mcron/config.scm])

mcron.c

@@ -22,6 +22,7 @@
    is needed because the crontab personality requires SUID which is not
    permitted for executable scripts.  */
 
+#include "config.h"
 #include <libguile.h>
 #include <signal.h>
 #include <stdlib.h>
@@ -35,7 +36,6 @@ static SCM set_cron_signals (void);
 int
 main (int argc, char **argv)
 {
-  setenv ("GUILE_LOAD_PATH", GUILE_LOAD_PATH, 1);
   scm_boot_guile (argc, argv, inner_main, 0);
 
   return EXIT_SUCCESS;
@@ -45,6 +45,14 @@ main (int argc, char **argv)
 static void
 inner_main (void *closure, int argc, char **argv)
 {
+  /* Set Guile load paths to ensure that Mcron modules will be found.  */
+  if (getenv ("MCRON_UNINSTALLED") == NULL)
+    {
+      scm_c_eval_string ("(set! %load-path (cons \""
+                         PACKAGE_LOAD_PATH "\" %load-path))");
+      scm_c_eval_string ("(set! %load-compiled-path (cons \""
+                         PACKAGE_LOAD_PATH "\" %load-compiled-path))");
+    }
   scm_set_current_module (scm_c_resolve_module ("mcron main"));
   /* Register set_cron_signals to be called from Guile.  */
   scm_c_define_gsubr ("c-set-cron-signals", 0, 0, 0, set_cron_signals);