bug#21650: fix should be underneath MH-E

[Katsumi Yamaoka]

On Wed, 03 Feb 2016 19:58:46 -0800, Mike Kupfer wrote:
> Bill Wohler wrote:

>> Katsumi Yamaoka <yamaoka@jpl.org> wrote:
>>> My solution is below.  Tested briefly.  This patch moves the
>>> binding of shr-inhibit-images and shr-blocked-images to Gnus
>>> from mm.  So, MH-E has to do a similar thing.
>>
>> I disagree. This only works for shr and defeats encapsulation.

> I think what makes this a non-trivial problem is wanting more
> flexibility than just a binary yes-no decision, which is what
> mm-inline-text-html-with-images currently provides.  That's why
> gnus-blocked-images is a regexp (or a function that returns a regexp).

> Could mm-inline-text-html-with-images be generalized to be more like
> gnus-blocked-images?  (For example, nil means don't retrieve anything, t
> means retrieve everything, a string would be a regexp of what URLs will
> be retrieved.)  Then shr could use mm-inline-text-html-with-images
> instead of shr-blocked-images, and MH-E users would have a single knob
> that could control any of the different rendering back-ends.

Ok, I was too near-sighted yesterday.  Here is a second try:

Implement the new user options in mm:
`mm-html-inhibit-images' --- boolean
  Non-nil means inhibit displaying of images inline in the article body.
  The default is t.
`mm-html-blocked-images' --- regexp or nil
  Regexp matching image URLs to be blocked.  The default is "".

Make `mm-inline-text-html-with-images' an obsolete variable alias
for `mm-html-inhibit-images'.

How Gnus does when calling an mm function:

(defun gnus-function ()
  (let ((mm-html-inhibit-images gnus-inhibit-images)
        (mm-html-blocked-images (with-current-buffer gnus-summary-buffer
                                  (gnus-blocked-images))))
    (mm-function)))

MH-E doesn't have to do like this if there's no need to have
options like `mh-inhibit-images'.

That's all.  Is this the right approach?

In Gnus, shr and gnus-html are controlled by both inhibit-images
and blocked-images, and w3m is controlled by only inhibit-images.
MH-E doesn't use gnus-html.el, does it?  As for mm-shr, it would
have to be changed into:

--- mm-decode.el~       2016-01-04 22:05:27.255542500 +0000
+++ mm-decode.el        2016-02-04 06:05:08.419602200 +0000
@@ -1846,11 +1846,5 @@
                                      (buffer-string))))))
-       shr-inhibit-images shr-blocked-images charset char)
-    (if (and (boundp 'gnus-summary-buffer)
-            (bufferp gnus-summary-buffer)
-            (buffer-name gnus-summary-buffer))
-       (with-current-buffer gnus-summary-buffer
-         (setq shr-inhibit-images gnus-inhibit-images
-               shr-blocked-images (gnus-blocked-images)))
-      (setq shr-inhibit-images gnus-inhibit-images
-           shr-blocked-images (gnus-blocked-images)))
+       (shr-inhibit-images mm-html-inhibit-images)
+       (shr-blocked-images mm-html-blocked-images)
+       charset char)
     (unless handle