[bug#45102] [PATCH 3/4] guix: 'guile' executable ignores GUILE_LOAD_PATH during startup.

["Ludovic Courtès" <ludo@gnu.org>]

When starting the 'guix' command, this ensures Guile modules are
immediately found instead of being search for in other directories.
This reduces the number of 'stat' calls during startup when
GUILE_LOAD_PATH is set to (almost) that of "env -i $(type -P guix)".

* gnu/packages/aux-files/guile-launcher.c (load_path)
(load_compiled_path): New variables.
(inner_main): Restore GUILE_LOAD_PATH and GUILE_LOAD_COMPILED_PATH and
set %load-path and %load-compiled-path accordingly.
(main): Save GUILE_LOAD_PATH and GUILE_LOAD_COMPILED_PATH and unset them.
---
 gnu/packages/aux-files/guile-launcher.c | 46 +++++++++++++++++++++++--
 1 file changed, 44 insertions(+), 2 deletions(-)

diff --git a/gnu/packages/aux-files/guile-launcher.c b/gnu/packages/aux-files/guile-launcher.c
index 886ede2846..1dd5d77e66 100644
--- a/gnu/packages/aux-files/guile-launcher.c
+++ b/gnu/packages/aux-files/guile-launcher.c
@@ -1,5 +1,5 @@
 /* GNU Guix --- Functional package management for GNU
-   Copyright 1996-1997,2000-2001,2006,2008,2011,2013,2018
+   Copyright 1996-1997,2000-2001,2006,2008,2011,2013,2018,2020
       Free Software Foundation, Inc.
    Copyright (C) 2020 Ludovic Courtès <ludo@gnu.org>
 
@@ -19,14 +19,47 @@
    along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* This file implements a variant of the 'guile' executable that does not
-   complain about locale issues.  */
+   complain about locale issues and arranges to reduce startup time by
+   ignoring GUILE_LOAD_PATH and GUILE_LOAD_COMPILED_PATH until it has
+   booted.  */
 
+#include <stdlib.h>
+#include <string.h>
 #include <locale.h>
 #include <libguile.h>
 
+/* Saved values of GUILE_LOAD_PATH and GUILE_LOAD_COMPILED_PATH.  */
+static const char *load_path, *load_compiled_path;
+
 static void
 inner_main (void *unused, int argc, char **argv)
 {
+  if (load_path != NULL)
+    {
+      setenv ("GUILE_LOAD_PATH", load_path, 1);
+      SCM load_path_var =
+	scm_c_public_lookup ("guile", "%load-path");
+      SCM addition =
+	scm_parse_path (scm_from_locale_string (load_path), SCM_EOL);
+      scm_variable_set_x (load_path_var,
+			  scm_append
+			  (scm_list_2 (scm_variable_ref (load_path_var),
+				       addition)));
+    }
+
+  if (load_compiled_path != NULL)
+    {
+      setenv ("GUILE_LOAD_COMPILED_PATH", load_compiled_path, 1);
+      SCM load_compiled_path_var =
+	scm_c_public_lookup ("guile", "%load-compiled-path");
+      SCM addition =
+	scm_parse_path (scm_from_locale_string (load_compiled_path), SCM_EOL);
+      scm_variable_set_x (load_compiled_path_var,
+			  scm_append
+			  (scm_list_2 (scm_variable_ref (load_compiled_path_var),
+				       addition)));
+    }
+
   scm_shell (argc, argv);
 }
 
@@ -40,6 +73,15 @@ main (int argc, char **argv)
        which is always preferable over the C locale.  */
     setlocale (LC_ALL, "en_US.utf8");
 
+  const char *str;
+  str = getenv ("GUILE_LOAD_PATH");
+  load_path = str != NULL ? strdup (str) : NULL;
+  str = getenv ("GUILE_LOAD_COMPILED_PATH");
+  load_compiled_path = str ? strdup (str) : NULL;
+
+  unsetenv ("GUILE_LOAD_PATH");
+  unsetenv ("GUILE_LOAD_COMPILED_PATH");
+
   scm_install_gmp_memory_functions = 1;
   scm_boot_guile (argc, argv, inner_main, 0);
   return 0; /* never reached */
-- 
2.29.2