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bug#59213: Emacs 29: Edebug fails to instrument a parameter whose name b
From: |
Alan Mackenzie |
Subject: |
bug#59213: Emacs 29: Edebug fails to instrument a parameter whose name begins with _ |
Date: |
Mon, 14 Nov 2022 10:28:29 +0000 |
Hello, Stefan.
On Sun, Nov 13, 2022 at 22:53:12 -0500, Stefan Monnier wrote:
> > In Emacs 29 (not started with -Q, but...),
> > I instrumented for edebug a function which looked like:
> > (defun c-trim-found-types (beg end _old-len) ....)
> > , the compilation being with lexical-binding: t.
> > During the edebug session, I attempted
> > e _old-len RET.
> The behavior depends on where you are in the *Backtrace* buffer, because
> each line in the backtrace can be in a different lexical scope.
> So please clarify on which line you were when you did the above.
I wasn't in the backtrace. I was stepping through the code in edebug.
More precisely, with this defun:
(defun add (a b _c)
(+ a b))
, instrument it for edebug. Call M-: (add 1 2 6).
The source code with active edebug now looks like:
(defun add (a b _c)
=>(+ a b))
.. e a now returns 1. e b returns 2. e _c gives the error message:
Error: Symbol's value as variable is void: _c
.. I repeat, this is a bug. It should have returned 6.
> > Instead of giving me the value of _old-len (which was 3) it gave the
> > error message
> > Error: Symbol's value as variable is void: _old-len
> > .. This is a bug.
> Could be. Or could be that you were trying to use `_old-len` in
> a lexical context where there is no such variable.
_c is in the same lexical context as a and b, surely?
> > Just because a function doesn't use a particular argument (here
> I think the leading underscore is purely incidental and you'd get the
> same behavior with `beg` and `end`.
No, beg and end returned their values. I admit I'm speculating about the
leading underscore, but I still say there's a bug, somewhere here.
> Stefan
--
Alan Mackenzie (Nuremberg, Germany).