From c097cc4282d868d5a3722fc5512f628cac9277a8 Mon Sep 17 00:00:00 2001
From: Fanael Linithien <fanael4@gmail.com>
Date: Tue, 16 Dec 2014 14:20:55 +0100
Subject: [PATCH] Add a :defaults "macro" to the :files spec.

This allows users to add files to the default file list without
overwriting it. For instance:

(example :fetcher example :url "http://example.com/"
         :files (:defaults "an.example"))

This would fetch Emacs Lisp (except tests) and Texinfo files, just like
the defaults, but unlike the defaults, the file an.example would be
included too.

:defaults is only recognized when it's the first element of :files.

Fixes #2275.
---
 README.md        | 5 +++++
 package-build.el | 9 ++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index d9fe4f32..451c99e6 100644
--- a/README.md
+++ b/README.md
@@ -246,6 +246,11 @@ to the root of the package.* More complex options are available,
 submit an [Issue](https://github.com/milkypostman/melpa/issues) if the
 specified package requires more complex file specification.
 
+    If the the package merely requires some additional files, for example for
+bundling external dependencies, but is otherwise fine with the defaults, it's
+recommended to use `:defaults` as the very first element of this list, which
+causes the default value shown above to be prepended to the specified file list.
+
 [git]: http://git-scm.com/
 [github]: https://github.com/
 [bzr]: http://bazaar.canonical.com/en/
diff --git a/package-build.el b/package-build.el
index 4bcb03e2..a6778a69 100644
--- a/package-build.el
+++ b/package-build.el
@@ -848,7 +848,14 @@ for ALLOW-EMPTY to prevent this error."
 
 (defun pb/config-file-list (config)
   "Get the :files spec from CONFIG, or return `package-build-default-files-spec'."
-  (or (plist-get config :files) package-build-default-files-spec))
+  (let ((file-list (plist-get config :files)))
+    (cond
+     ((null file-list)
+      package-build-default-files-spec)
+     ((eq :default (car file-list))
+      (append package-build-default-files-spec (cdr file-list)))
+     (t
+      file-list))))
 
 (defun pb/expand-source-file-list (dir config)
   "Shorthand way to expand paths in DIR for source files listed in CONFIG."