core: fix spacelpa support

* new variable configuration-layer-stable-elpa-archive
* add missing sub-directory "packages"
* update .lock file with above changes and bump to archive version 0.400

.lock

@@ -1,16 +1,17 @@
 ;; -*- mode: emacs-lisp -*-
 
 (setq configuration-layer-stable-elpa-name "spacelpa")
-(setq configuration-layer-stable-elpa-version "0.300")
+(setq configuration-layer-stable-elpa-version "0.400")
+(setq configuration-layer-stable-elpa-archive (concat configuration-layer-stable-elpa-directory
+                                     "spacelpa-"
+                                     configuration-layer-stable-elpa-version))
 (setq configuration-layer-elpa-subdirectory "develop")
 
 (setq configuration-layer-elpa-archives
   `(("melpa"    . "melpa.org/packages/")
     ("org"      . "orgmode.org/elpa/")
     ("gnu"      . "elpa.gnu.org/packages/")
-    ("spacelpa" . ,(concat configuration-layer-stable-elpa-directory
-                           "spacelpa-"
-                           configuration-layer-stable-elpa-version))))
+    ("spacelpa" . ,(concat configuration-layer-stable-elpa-archive "/packages/"))))
 
 (setq package-archive-priorities
       '(("spacelpa" . 8)

core/core-configuration-layer.el

@@ -53,7 +53,7 @@
   "Absolute path to the lock file.")
 
 (defvar configuration-layer-stable-elpa-version spacemacs-version
-  "Version of ELPA stable repository. This value is aimed to be overwritten by
+  "Version of ELPA stable repository. This value is aimed to be defined in
 the .lock file at the root of the repository.")
 
 (defvar configuration-layer-stable-elpa-name "spacelpa"
@@ -68,6 +68,10 @@ the lock file.")
    (concat spacemacs-cache-directory "stable-elpa/" emacs-version "/"))
   "Remote location of the tarball for the ELPA stable directory")
 
+(defconst configuration-layer-stable-elpa-archive nil
+  "Absolute path to stable ELPA directory. This value is aimed to be defined in
+the .lock file at the root of the repository.")
+
 (defconst configuration-layer--stable-elpa-tarball-directory
   "https://github.com/syl20bnr/spacelpa/archive/"
   "Remote location of the tarball for the ELPA stable directory")
@@ -2589,8 +2593,7 @@ repository."
 
 (defun configuration-layer//stable-elpa-directory ()
   "Return the local absolute path of the ELPA stable repository."
-  (cdr (assoc configuration-layer-stable-elpa-name
-              configuration-layer-elpa-archives)))
+  configuration-layer-stable-elpa-archive)
 
 (defun configuration-layer//stable-elpa-tarball-local-file ()
   "Return the local absolute path for the file of the downloaded tarball of