GNU bug report logs - #76748
31.0.50; `unload-feature' unbinds NEW-ALIAS and BASE-VARIABLE of variable alias

Previous Next

Full log

View this message in rfc822 format

From: Jens Schmidt <jschmidt4gnu <at> vodafonemail.de>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 76748 <at> debbugs.gnu.org
Subject: bug#76748: 31.0.50; `unload-feature' unbinds NEW-ALIAS and BASE-VARIABLE of variable alias
Date: Fri, 14 Mar 2025 23:14:05 +0100

[Message part 1 (text/plain, inline)]

On 2025-03-12  23:53, Stefan Monnier wrote:

> You could also choose to keep that function "internal"
> and not document it in the manual/NEWS (like we did for
> `internal-make-var-non-special`), mostly justified in case its
> semantics is delicate/messy/ugly.

I decided to do exactly that - if anybody else except `unload-feature'
is ever going to need that function, she/he can do the documentation.
Will add some tests, anyway, when the rest of this has been decided
upon.

Adding the function `internal-delete-indirect-variable' and calling it
from loadhist.el was easy enough (too easy?), please see the attached
patch for a first draft.  I decided that the right way to unbind an
alias, as far as `unload-feature' is concerned, is to make it a regular
variable and unbind that.

More questions:

1. I have a bad feeling about butting in between 1st class citizens
   makunbound and fmakunbound in data.c, but couldn't find a better
   other place for that function.

2. Before or after switching the variable from an alias to a plain one
   in `internal-delete-indirect-variable', do I somehow need to clean or
   zero ...val->alias before overwriting it as ...val->value with
   "Fset (symbol, Qunbound);"?

3. defvaralias attaches the new alias to the load history as symbol.
   One could also attach it as (Fcons (Qalias, new_alias)) and provide a
   new cl method loadhist-unload-element for that case instead of handling
   aliases together with regular symbols.

Finally, `defvaralias' and `define-obsolete-variable-alias' have a
number of other side-effects, which I have not covered in function
`internal-delete-indirect-variable'.  Please let me know if I should
care about any of these:

4. defvaralias potentially calls

     notify_variable_watchers (new_alias, base_variable, Qdefvaralias, Qnil);

5. defvaralias declares both new alias and base symbol as special.

6. defvaralias sets

     XSYMBOL (new_alias)->u.s.trapped_write =
       XSYMBOL (base_variable)->u.s.trapped_write;

7. defvaralias puts the alias docstring into the variable-documentation
   property.

8. define-obsolete-variable-alias copies properties `saved-value',
   `saved-variable-comment'  from the obsolete to the non-obsolete
   symbol.

9. define-obsolete-variable-alias sets property `byte-obsolete-variable'
   on the obsolete symbol.

Thanks.

[0001-Correctly-unload-variable-aliases.patch (text/x-patch, attachment)]

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.