[PATCH 3/3] emacs: Work around gnus-inhibit-images bug in mm-shr

[Austin Clements <amdragon@MIT.EDU>]

Emacs 24's mm-shr HTML email renderer fails to load gnus-art before
referencing gnus-inhibit-images, resulting in a void-variable error
when notmuch attempts to render an HTML email with inline images.
This works around this bug by providing a definition for
gnus-inhibit-images.

This fixes the "Rendering HTML mail with images" test for Emacs 24.
---
 emacs/notmuch-lib.el |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/emacs/notmuch-lib.el b/emacs/notmuch-lib.el
index 20d990d..c74035c 100644
--- a/emacs/notmuch-lib.el
+++ b/emacs/notmuch-lib.el
@@ -254,6 +254,30 @@ the given type."
   (or (plist-get part :content)
       (notmuch-get-bodypart-internal (notmuch-id-to-query (plist-get msg :id)) nth process-crypto)))
 
+;; Workaround: The call to `mm-display-part' below triggers a bug in
+;; Emacs 24 if it attempts to use the shr renderer to display an HTML
+;; part with images in it (demonstrated in 24.1 and 24.2 on Debian and
+;; Fedora 17, though unreproducable in other configurations).
+;; `mm-shr' references the variable `gnus-inhibit-images' without
+;; first loading gnus-art, which defines it, resulting in a
+;; void-variable error.  Unfortunately, gnus-art and its dependencies
+;; are very large and often not needed, making it undesirable to
+;; simply load gnus-art here.  Instead, we directly define the
+;; variable here.  We use defcustom instead of defvar so that it
+;; interacts properly with user customizations of the variable (if the
+;; custom value has already been loaded, only defcustom will make it
+;; visible).  There is a danger of overriding the documentation string
+;; if gnus-art is already loaded, so we don't do anything if the
+;; variable is already defined.  If the user attempts to customize the
+;; variable, we instruct custom to load gnus-art before displaying the
+;; widget, which will override this definition with the proper
+;; documentation string, groups, etc.
+(if (and (>= emacs-major-version 24)
+         (not (boundp 'gnus-inhibit-images)))
+    (defcustom gnus-inhibit-images nil
+      "Documentation will be available after loading gnus-art."
+      :load "gnus-art"))
+
 (defun notmuch-mm-display-part-inline (msg part nth content-type process-crypto)
   "Use the mm-decode/mm-view functions to display a part in the
 current buffer, if possible."
-- 
1.7.10