Support environment variables to override USER & SYSTEM resource paths

Even though individual USER/SYSTEM paths could be set using environment variables,
it wasn't possible to override the USER or SYSTEM paths.

This meant the result of `bpy.utils.resource_path('USER')` &
`bpy.utils.resource_path('SYSTEM')` could still be used by scripts,
making the Blender session potentially the default USER directory
(even when `BLENDER_USER_CONFIG`, `BLENDER_USER_SCRIPTS` &
`BLENDER_USER_DATAFILES` all point elsewhere).

Resolve by adding environment variables:

- BLENDER_USER_RESOURCES
- BLENDER_SYSTEM_RESOURCES

These will be used for `bpy.utils.resource_path('USER')` &
`bpy.utils.resource_path('SYSTEM')`, as well as a basis for user &
system directories, unless those environment variables are
set (`BLENDER_USER_*` or `BLENDER_SYSTEM_*`).

Resolves issue raised by T101389.

Example usage & output:

{P3225}

Reviewed By: brecht

Ref D16111

1 files changed, 22 insertions, 14 deletions

diff --git a/source/blender/blenkernel/intern/appdir.c b/source/blender/blenkernel/intern/appdir.c
index e3c42c8bb78..7c409f1095b 100644
--- a/source/blender/blenkernel/intern/appdir.c
+++ b/source/blender/blenkernel/intern/appdir.c
@@ -460,18 +460,22 @@ static bool get_path_user_ex(char *targetpath,
                              const bool check_is_dir)
 {
   char user_path[FILE_MAX];
-  const char *user_base_path;
 
-  /* for portable install, user path is always local */
-  if (BKE_appdir_app_is_portable_install()) {
-    return get_path_local_ex(
-        targetpath, targetpath_len, folder_name, subfolder_name, version, check_is_dir);
+  if (test_env_path(user_path, "BLENDER_USER_RESOURCES", check_is_dir)) {
+    /* Pass. */
   }
-  user_path[0] = '\0';
+  else {
+    /* for portable install, user path is always local */
+    if (BKE_appdir_app_is_portable_install()) {
+      return get_path_local_ex(
+          targetpath, targetpath_len, folder_name, subfolder_name, version, check_is_dir);
+    }
+    user_path[0] = '\0';
 
-  user_base_path = GHOST_getUserDir(version, blender_version_decimal(version));
-  if (user_base_path) {
-    BLI_strncpy(user_path, user_base_path, FILE_MAX);
+    const char *user_base_path = GHOST_getUserDir(version, blender_version_decimal(version));
+    if (user_base_path) {
+      BLI_strncpy(user_path, user_base_path, FILE_MAX);
+    }
   }
 
   if (!user_path[0]) {
@@ -518,7 +522,6 @@ static bool get_path_system_ex(char *targetpath,
                                const bool check_is_dir)
 {
   char system_path[FILE_MAX];
-  const char *system_base_path;
   char relfolder[FILE_MAX];
 
   if (folder_name) { /* `subfolder_name` may be NULL. */
@@ -528,10 +531,15 @@ static bool get_path_system_ex(char *targetpath,
     relfolder[0] = '\0';
   }
 
-  system_path[0] = '\0';
-  system_base_path = GHOST_getSystemDir(version, blender_version_decimal(version));
-  if (system_base_path) {
-    BLI_strncpy(system_path, system_base_path, FILE_MAX);
+  if (test_env_path(system_path, "BLENDER_SYSTEM_RESOURCES", check_is_dir)) {
+    /* Pass. */
+  }
+  else {
+    system_path[0] = '\0';
+    const char *system_base_path = GHOST_getSystemDir(version, blender_version_decimal(version));
+    if (system_base_path) {
+      BLI_strncpy(system_path, system_base_path, FILE_MAX);
+    }
   }
 
   if (!system_path[0]) {