bug#31793: 26.1; (error "Lisp nesting exceeds ‘max-lisp-eval-depth’")

[John Shahid]

Leo Liu <sdl.web@gmail.com> writes:

> On 2018-06-12 08:21 +0300, Eli Zaretskii wrote:
>> Ugh, macOS...  This means no xbacktrace and no other GDB
>> wizardry...
>
> Indeed.
>
>> Well, I think the most important thing is to produce a Lisp
>> backtrace from the error.
>
> Turns out 26.1 cannot load a version of python.el (by dave love) that I
> have in my site-lisp.
>
> 1. emacs -Q -l python.el
> 2. M-x python-mode
>
> ,----[ error ]
> | Variable binding depth exceeds max-specpdl-size
> | Error in post-command-hook (global-eldoc-mode-check-buffers): (error 
> "Variable binding depth exceeds max-specpdl-size")
> `----
>
> Gnus was just loading python-mode to fontify some code in an article.

double posting since I sent the email only to Leo.

VVVV original email VVVV

That seems to be a result of converting `global-eldoc-mode' to use
`define-globalized-minor-mode' in 2349f. The recursive call seems to be
a result of the following sequence of calls:

1. python-mode is enabled which adds an eldoc-mode-hook
2. eldoc-mode is turned on in the buffer triggering python's
eldoc-mode-hook
3. python-mode hook will start an inferior process which in turn trigger
,MODE-enable-in-buffers
4. ,MODE-enable-in-buffers will go over the list again trying to enable
eldoc-mode

The problem is in step 4. The eldoc-global-mode buffer list isn't reset
in step 2. Step 4 will try to enabe the mode for the same buffer and
start a sequence of calls at 2. I was able to fix this problem by
setting the buffer-list to nil inside ,MODE-enable-in-buffers. I
attached a patch below.

>From 9f6bb1c2d9cac8ccea129242d6977bc848b3f715 Mon Sep 17 00:00:00 2001
From: John Shahid <jvshahid@gmail.com>
Date: Sat, 23 Jun 2018 11:12:44 -0400
Subject: [PATCH] avoid turning on the global-minor-mode recursively

* lisp/emacs-lisp/easy-mmode.el (define-globalized-minor-mode): reset
  the buffer-list inside ,MODE-enable-in-buffers to avoid enabling the
  mode recursively
---
 lisp/emacs-lisp/easy-mmode.el | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lisp/emacs-lisp/easy-mmode.el b/lisp/emacs-lisp/easy-mmode.el
index a81b6fefb2..d363634236 100644
--- a/lisp/emacs-lisp/easy-mmode.el
+++ b/lisp/emacs-lisp/easy-mmode.el
@@ -457,7 +457,9 @@ define-globalized-minor-mode
 
        ;; The function that calls TURN-ON in each buffer.
        (defun ,MODE-enable-in-buffers ()
-        (dolist (buf ,MODE-buffers)
+         (let ((buffers ,MODE-buffers))
+           (setq ,MODE-buffers nil)
+           (dolist (buf buffers)
           (when (buffer-live-p buf)
             (with-current-buffer buf
                (unless ,MODE-set-explicitly
@@ -467,12 +469,11 @@ define-globalized-minor-mode
                         (,mode -1)
                         (funcall #',turn-on))
                     (funcall #',turn-on))))
-              (setq ,MODE-major-mode major-mode)))))
+                 (setq ,MODE-major-mode major-mode))))))
        (put ',MODE-enable-in-buffers 'definition-name ',global-mode)
 
        (defun ,MODE-check-buffers ()
         (,MODE-enable-in-buffers)
-        (setq ,MODE-buffers nil)
         (remove-hook 'post-command-hook ',MODE-check-buffers))
        (put ',MODE-check-buffers 'definition-name ',global-mode)
 
-- 
2.17.1