Subject: 29.1.90; eww: error when eww-retrieve-command is set to 'sync

From: Phil Sainty <[email-masked]>
Date: Tue, 09 Jan 2024 15:54:55 +1300

Customize `eww-retrieve-command' to `sync' -- the customize label
is "Use `url-retrieve-synchronously'" -- or simply:

  (setq eww-retrieve-command 'sync)

Now any `eww' invocation fails with:

apply: Wrong type argument: stringp, nil

I see the error in my builds of 29 and 30, but not in 28.2.

My 30.0.50 build dated back to 2023-09-21, so I've just
compiled a fresh build of 30 and no longer see the *error*,
but it still doesn't work -- the page is never rendered.

Example in Emacs 29:

  (setq eww-retrieve-command 'sync)
  (eww "http://example.com")

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
   eww-render(nil "http://example.com/" "http://example.com/" nil 
#<buffer *eww*>)
   apply(eww-render nil "http://example.com/" ("http://example.com/" nil 
#<buffer *eww*>))
   eww-retrieve("http://example.com/" eww-render ("http://example.com/" 
nil #<buffer *eww*>))
   eww("http://example.com")

Or after loading the uncompiled eww.el:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
   set-buffer(nil)
   (save-current-buffer (set-buffer buffer) (plist-put eww-data :peer 
(plist-get status :peer)) (setq list-buffers-directory url) (setq 
url-current-lastloc (url-generic-parse-url url)))
   ...
   eww-render(nil "http://example.com/" "http://example.com/" nil 
#<buffer *eww*>)

That BUFFER arg to `set-buffer' looks like it's nil on account
of an additional duplicate argument passed to `eww-render':

   eww-render(nil "http://example.com/" "http://example.com/" nil 
#<buffer *eww*>)

should have been:

   eww-render(nil "http://example.com/" nil #<buffer *eww*>)

So I think the bug is the last line here:

  (defun eww-retrieve (url callback cbargs)
    (cond
     ((null eww-retrieve-command)
      (url-retrieve url #'eww-render cbargs))
     ((eq eww-retrieve-command 'sync)
      (let ((data-buffer (url-retrieve-synchronously url)))
        (with-current-buffer data-buffer
          (apply #'eww-render nil url cbargs))))

Where cbargs evidentially contains the URL already, so it
should presumably be:

  (apply #'eww-render nil cbargs)

I can confirm that this change fixes my example case (but I haven't
tried to find out if the situation is more complicated than that).

-Phil

In GNU Emacs 29.1.90 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
  version 1.16.0, Xaw scroll bars) of 2023-10-24 built on phil-lp
Repository revision: cc3e436c822343f72f3ede6b638e1b68cd434583
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 
11.0.12101004
System Description: Ubuntu 22.04.3 LTS

Configured using:
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