Don't try to use our custom packages unless pinned

They do not have src set, so if we pull them in without having a pin
they fail to build.

Noticed with org, so add a test for that. Probably not the only one
affected, though.

Fixes #4

checks.nix

@@ -75,4 +75,7 @@ in {
   };
   interactive = doomTest "minimal" { config = [ "default" ]; } { };
   interactive-without-loader = doomTest "minimal" { config = [ "default" ]; } { profileName = ""; };
+
+  # Various tests of module combinations.
+  unpinned-org = doomTest "external-org" { app = [ [ "rss" "+org" ] ]; } { };
 }

default.nix

@@ -176,9 +176,10 @@ let
               origEPkg == esuper.elpaPackages.${name} or null
               || origEPkg == esuper.nongnuPackages.${name} or null);
             epkg =
-              customPackages.${name}
-                or (if !hasOrigEPkg || (p ? pin && isElpa)
-              then
+              if hasOrigEPkg && (pin != null -> !(isElpa || customPackages ? ${name}))
+              then origEPkg
+              else customPackages.${name}
+                or (
                 assert lib.assertMsg
                   (isElpa || (p ? recipe && pin != null) || extraUrls ? ${name})
                   "${name}: not in epkgs, not elpa, no recipe or not pinned";
@@ -224,8 +225,7 @@ let
                   # TODO: refactor out the recursive call to makePackage.
                   # (Currently needed for dependencies on packages not in epkgs or doom.)
                   packageRequires = map (name: eself.${name} or (makePackage name {})) reqlist;
-                }
-                else origEPkg);
+                });
             url =
               if (p.recipe.host or "") == "github" && p ? recipe.repo
               then "https://github.com/${p.recipe.repo}"

tests.el

@@ -23,6 +23,13 @@
   ;; The minimal test is a noop.
   )
 
+(defun test-external-org ()
+  "Test org can be loaded and it's not built-in."
+  (require 'org)
+  (let ((path (find-library-name "org")))
+    (unless (string-search "/site-lisp/" path)
+      (error "org-mode probably built-in: %s" path))))
+
 (defun test-doom ()
   (let* ((out (getenv "out"))
          (test (intern-soft (format "test-%s" (getenv "testName"))))