Subject: 26.0.50; Error using Edebug on code that uses cl-defmethod

From: Gemini Lasswell <[email-masked]>
Date: Fri, 21 Oct 2016 08:15:02 -0700

Edebug gets confused after instrumenting multiple methods with the same
name created by cl-defgeneric and cl-defmethod. To reproduce, save the
following bit of code (which is an excerpt from cl-generic-tests.el)
to bug.el:

(require 'cl-generic)

(fmakunbound 'foo)
(cl-defgeneric foo (x y))
(cl-defgeneric (setf foo) (v y z) "My generic doc.")
(cl-defmethod (setf foo) (v (y t) z) (list v y z))
(cl-defmethod (setf foo) (v (_y (eql 4)) z) (list v "four!" z))

(defun foo-bug ()
  (message "%s" (setf (foo 'a 'b) 'v)))

(foo-bug)

Steps to reproduce:
1. emacs -Q
2. C-x C-f bug.el RET
3. M-x edebug-all-defs RET
4. M-x eval-buffer RET
5. g

Result: edebug--display: Args out of range: [44 51 61 62], 4

The trouble seems to be that Edebug is attaching its per-definition data
for both methods to the same symbol, setf@foo. I found that
changing the relevant line in cl-defmethod's Edebug spec from this:

             [&or name ("setf" :name setf name)]

to this:

             [&or symbolp ("setf" symbolp)]

makes the problem go away by creating new anonymous symbols for the
methods. Although if you want to try this out interactively, you'll need
to set edebug-form-data to nil for the buffer, because otherwise Edebug
will remember the previous name you gave the definition and reuse it.

While I was looking at the Edebug spec for cl-defmethod, I also noticed
that it uses list to match the argument list. Edebug is going to treat
list as a predicate, and list is going to return a non-nil value for
whatever is in that match position. I don't know of any real problem
that could cause, but using listp would be more correct.

In GNU Emacs 26.0.50.4 (x86_64-apple-darwin15.6.0, NS appkit-1404.47 Version 10.11.6 (Build 15G1004))
 of 2016-10-20 built on rainbow.local
Repository revision: 9e1e257ea8605354d15b4bd93e0af6188aae40db
Windowing system distributor 'Apple', version 10.3.1404
Recent messages:
Mark set
Replaced 8 occurrences
Quit
nil
Edebug: setf@foo [2 times]
Edebug: foo-bug
Go...
edebug--display: Args out of range: [44 51 61 62], 4
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