configuration: Have environment variables override configuration.

Because the configuration file is systematically written when
RetroArch terminates, persisting any previous default/configured
value, setting the LIBRETRO_DIRECTORY, LIBRETRO_ASSETS_DIRECTORY, etc.
environment variables would not have an effect unless the
retroarch.cfg configuration file was cleared.

This seems to go against the common expectation that environment
variables are set by users to *override* the default behavior or
configuration of an application.

* configuration.c (config_load_file) <libretro_directory>
<libretro_assets_directory, libretro_autoconfig_directory>
<libretro_video_filter_directory, libretro_video_shader_directory> :
New variables. Use the values of the LIBRETRO_DIRECTORY,
LIBRETRO_ASSETS_DIRECTORY,
LIBRETRO_AUTOCONFIG_DIRECTORY, LIBRETRO_VIDEO_FILTER_DIRECTORY
and LIBRETRO_VIDEO_SHADER_DIRECTORY environment variables
instead of their corresponding configured values, when set.
* docs/retroarch.6: Document the environment variables honored and
their behavior.

configuration.c

@@ -3573,6 +3573,11 @@ static bool config_load_file(global_t *global,
 {
    unsigned i;
    char tmp_str[PATH_MAX_LENGTH];
+   char* libretro_directory                        = NULL;
+   char* libretro_assets_directory                 = NULL;
+   char* libretro_autoconfig_directory             = NULL;
+   char* libretro_video_filter_directory           = NULL;
+   char* libretro_video_shader_directory           = NULL;
    static bool first_load                          = true;
    bool without_overrides                          = false;
    unsigned msg_color                              = 0;
@@ -3848,19 +3853,27 @@ static bool config_load_file(global_t *global,
          strlcpy(path_settings[i].ptr, tmp_str, PATH_MAX_LENGTH);
    }
 
-#if !IOS
-   if (config_get_path(conf, "libretro_directory", tmp_str, sizeof(tmp_str)))
-      configuration_set_string(settings,
-            settings->paths.directory_libretro, tmp_str);
-#endif
-
 #ifdef RARCH_CONSOLE
    if (conf)
       video_driver_load_settings(global, conf);
 #endif
 
    /* Post-settings load */
 
+   libretro_directory = getenv("LIBRETRO_DIRECTORY");
+   if (libretro_directory) {
+      configuration_set_string(settings,
+            settings->paths.directory_libretro, libretro_directory);
+      configuration_set_string(settings,
+            settings->paths.path_libretro_info, libretro_directory);
+   }
+
+   libretro_autoconfig_directory = getenv("LIBRETRO_AUTOCONFIG_DIRECTORY");
+   if (libretro_autoconfig_directory)
+       configuration_set_string(settings,
+				settings->paths.directory_autoconfig,
+				libretro_autoconfig_directory);
+
    if (     (rarch_flags & RARCH_FLAGS_HAS_SET_USERNAME)
          && (override_username))
    {
@@ -4032,15 +4045,27 @@ static bool config_load_file(global_t *global,
       *settings->paths.path_menu_wallpaper = '\0';
    if (string_is_equal(settings->paths.path_rgui_theme_preset, "default"))
       *settings->paths.path_rgui_theme_preset = '\0';
-   if (string_is_equal(settings->paths.directory_video_shader, "default"))
+   libretro_video_shader_directory = getenv("LIBRETRO_VIDEO_SHADER_DIRECTORY");
+   if (libretro_video_shader_directory) { /* override configuration value */
+      configuration_set_string(settings, settings->paths.directory_video_shader,
+			       libretro_video_shader_directory);
+   } else if (string_is_equal(settings->paths.directory_video_shader, "default"))
       *settings->paths.directory_video_shader = '\0';
-   if (string_is_equal(settings->paths.directory_video_filter, "default"))
+   libretro_video_filter_directory = getenv("LIBRETRO_VIDEO_FILTER_DIRECTORY");
+   if (libretro_video_filter_directory) { /* override configuration value */
+       configuration_set_string(settings, settings->paths.directory_video_filter,
+				libretro_video_filter_directory);
+   } else if (string_is_equal(settings->paths.directory_video_filter, "default"))
       *settings->paths.directory_video_filter = '\0';
    if (string_is_equal(settings->paths.directory_audio_filter, "default"))
       *settings->paths.directory_audio_filter = '\0';
    if (string_is_equal(settings->paths.directory_core_assets, "default"))
       *settings->paths.directory_core_assets = '\0';
-   if (string_is_equal(settings->paths.directory_assets, "default"))
+   libretro_assets_directory = getenv("LIBRETRO_ASSETS_DIRECTORY");
+   if (libretro_assets_directory) { /* override configuration value */
+      configuration_set_string(settings,
+           settings->paths.directory_assets, libretro_assets_directory);
+   } else if (string_is_equal(settings->paths.directory_assets, "default"))
       *settings->paths.directory_assets = '\0';
 #ifdef _3DS
    if (string_is_equal(settings->paths.directory_bottom_assets, "default"))

docs/retroarch.6

@@ -1,6 +1,6 @@
 .\" retroarch.6:
 
-.TH  "RETROARCH" "6" "November 1, 2011" "RETROARCH" "System Manager's Manual: retroarch"
+.TH  "RETROARCH" "6" "September 28, 2024" "RETROARCH" "System Manager's Manual: retroarch"
 
 .SH NAME
 
@@ -239,3 +239,36 @@ Disables all kinds of content patching.
 .TP
 \fB-D, --detach\fR
 Detach from the current console. This is currently only relevant for Microsoft Windows.
+
+.SH ENVIRONMENT
+\fBretroarch\fR honors the following environment variables:
+
+.TP
+\fBLIBRETRO_DIRECTORY\fR
+Specify the directory where RetroArch looks for core and info files,
+overriding the value of the "libretro_directory" configuration file
+option.
+
+.TP
+\fBLIBRETRO_ASSETS_DIRECTORY\fR
+Specify the directory where RetroArch looks for assets, overriding
+the value of the "assets_directory" configuration file
+option.
+
+.TP
+\fBLIBRETRO_AUTOCONFIG_DIRECTORY\fR
+Specify the directory where RetroArch looks for controller
+auto-configuration files, overriding the value of the
+"joypad_autoconfig_dir" configuration file option.
+
+.TP
+\fBLIBRETRO_VIDEO_FILTER_DIRECTORY\fR
+Specify the directory where RetroArch looks for video filters,
+overriding the value of the "video_filter_dir" configuration file
+option.
+
+.TP
+\fBLIBRETRO_VIDEO_SHADER_DIRECTORY\fR
+Specify the directory where RetroArch looks for video shaders,
+overriding the value of the "video_shader_dir" configuration file
+option.