allow to pin packages to specific archive

core/core-configuration-layer.el

@@ -183,7 +183,8 @@ LAYER has to be installed for this method to work properly."
 (defvar configuration-layer--elpa-archives
   '(("melpa" . "melpa.org/packages/")
     ("org"   . "orgmode.org/elpa/")
-    ("gnu"   . "elpa.gnu.org/packages/"))
+    ("gnu"   . "elpa.gnu.org/packages/")
+    ("melpa-stable" . "stable.melpa.org/packages/"))
   "List of ELPA archives required by Spacemacs.")
 
 (defvar configuration-layer-exclude-all-layers nil
@@ -499,6 +500,7 @@ If TOGGLEP is nil then `:toggle' parameter is ignored."
   (let* ((name-sym (if (listp pkg) (car pkg) pkg))
          (name-str (symbol-name name-sym))
          (location (when (listp pkg) (plist-get (cdr pkg) :location)))
+         (archive (when (listp pkg) (plist-get (cdr pkg) :archive)))
          (min-version (when (listp pkg) (plist-get (cdr pkg) :min-version)))
          (step (when (listp pkg) (plist-get (cdr pkg) :step)))
          (excluded (when (listp pkg) (plist-get (cdr pkg) :excluded)))
@@ -518,6 +520,8 @@ If TOGGLEP is nil then `:toggle' parameter is ignored."
                        (configuration-layer/get-layer-local-dir
                         (oref layer :name))
                        name-str name-str)))))
+    (when archive
+      (configuration-layer/pin-package name-sym archive))
     (when location (oset obj :location location))
     (when min-version (oset obj :min-version (version-to-list min-version)))
     (when step (oset obj :step step))
@@ -1934,6 +1938,19 @@ FILE-TO-LOAD is an explicit file to load after the installation."
             (1+ configuration-layer-error-count))
     (setq configuration-layer-error-count 1)))
 
+(defun configuration-layer/pin-package (package archive)
+  "Pin PACKAGE to ARCHIVE.
+
+When PACKAGE is pinned to specific ARCHIVE, it is installed
+exactly from that ARCHIVE.
+
+ARCHIVE must be one of the following symbols: melpa, org, gnu,
+melpa-stable."
+  (let ((archive-name (symbol-name archive)))
+    (unless (assoc archive-name package-archives)
+    (error "Archive '%s' is not supported." archive))
+  (push (cons package archive-name) package-pinned-packages)))
+
 (provide 'core-configuration-layer)
 
 ;;; core-configuration-layer.el ends here

doc/LAYERS.org

@@ -328,6 +328,9 @@ as follows:
                              :fetcher github
                              :repo "some/repo"))
 
+    ;; A pinned package
+    (some-package :archive melpa-stable)
+
     ;; An excluded package
     (some-package :excluded t)
     ))
@@ -338,6 +341,8 @@ currently supports packages on ELPA compliant repositories, local packages and
 MELPA recipes (through the Quelpa package). See the [[https://github.com/milkypostman/melpa#recipe-format][MELPA documentation]] for more
 information about recipes.
 
+By using =:archive= attribute one can pin specific package to specific archive.
+
 Packages may be /excluded/ by setting the =:excluded= property to true. This
 will prevent the package from being installed even if it is used by another
 layer.