Re: pcase map binding form expansion failure on Emacs 27 only

[Kevin Vigouroux via "Emacs development discussions." <emacs-devel@gnu.org>]

Adam Porter <adam@alphapapa.net> writes:

> I am not using the version of map.el included with Emacs 27.2.  As I
> wrote in the original message.

>> What does the compiler really generate?

> It generates an incorrect macro expansion, which causes the eager macro
> expansion/void-variable errors which precipitated this thread.

However, in my test, the macro expansion returns a good result. Why?

It seems to me that I proceeded as indicated by first loading ‘map v3.1’
and then compiling the code.

#+begin_quote
;ELC\0\0
;;; Compiled
;;; in Emacs version 27.2
;;; with all optimizations.

;;; This file uses dynamic docstrings, first added in Emacs 19.29.

;;; This file does not contain utf-8 non-ASCII characters,
;;; and so can be loaded in Emacs versions earlier than 23.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


(defvar plist (list :max-height 3 :max-width 2))
(byte-code "\300\301\302\303!\"\207" [message "EXPANSION TEST: %S" macroexpand-all (pcase-let* (((map :max-width) plist)) max-width)] 4)
#+end_quote

The message displayed in the echo area is:

#+begin_quote
EXPANSION TEST: (let* ((x3 (map-elt plist :max-width))) (let ((max-width x3)) max-width))
#+end_quote

> I'm not sure you understand the problem I'm describing.  Please see my
> original message.

>> Looking at things again, I'm not sure that imposing a given version for
>> a package is a good thing.

> I don't know what you mean by "imposing a given version for a package."
> The "Package-Requires" header instructs package.el to ensure that
> certain dependencies are installed at certain minimum versions.  This is
> a standard practice in Emacs packages.

Maybe I’m not right.
-- 
Best regards,
Kevin Vigouroux