bug#30101: 25.3; defcustom does not clear old :options when reevaluated

[Mauro Aranda <maurooaranda@gmail.com>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> * doc/lispref/customize.texi (Defining Customization Variables):
>                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> The name in parentheses should be the name of the node, not of the
> section.

Right, sorry.

>> +Re-evaluating a @code{defcustom} form of an already defined user
>> +option does not clear the reasonable values added by previous
>> +evaluations, or by calls to @code{custom-add-frequent-value}.  This
>> +way, Lisp programs can add reasonable values for user options not yet
>> +defined.
>
> This doesn't emphasize the fact that you are talking about
> reevaluation after changing the option's values.  Without that, this
> text doesn't drive the point home.

Then perhaps it makes sense to split the paragraph, and talk about that
when describing the :options keyword?  I did that in this new patch.

> Also, I'd suggest to drop the "reasonable" part, as it gets in the way
> of understanding the important parts by distracting the reader to
> think about what "reasonable" means in this context.

Fair enough.  Dropped it.

>> --- a/lisp/custom.el
>> +++ b/lisp/custom.el
>> @@ -578,9 +578,14 @@ custom-add-dependencies
>>  (defun custom-add-option (symbol option)
>>    "To the variable SYMBOL add OPTION.
>>
>> +Custom then presents OPTION to the user as a suggested member
>> +for the value of SYMBOL.
>> +
>>  If SYMBOL's custom type is a hook, OPTION should be a hook member.
>> -If SYMBOL's custom type is an alist, OPTION specifies a symbol
>> -to offer to the user as a possible key in the alist.
>> +If SYMBOL's custom type is an alist, OPTION specifies a possible key
>> +in the alist.
>> +Similarly, if SYMBOL's custom type is a plist, OPTION specifies
>> +a possible name in the plist.
>>  For other custom types, this has no effect."
>
> I don't think I understand what this tries to accomplish, or how it is
> relevant to the issue discussed here.

The docstring didn't mention what was the effect if SYMBOL was a plist,
so I thought I'd take the chance of improving the docstring for the
function that also affects the suggested values.  But maybe that can be
left for another patch, so I dropped it in this new one.

Thanks for reviewing, I hope this patch is better.

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From 14c226017b0e868cf68aef8f4d3b9a1e8cd94ab7 Mon Sep 17 00:00:00 2001
From: Mauro Aranda <maurooaranda@gmail.com>
Date: Sat, 29 Aug 2020 13:07:32 -0300
Subject: [PATCH] Improve documentation for custom :options

* doc/lispref/customize.texi (Variable Definitions):
Mention that re-evaluating a defcustom form doesn't reset custom
options.  (Bug#30101)
---
 doc/lispref/customize.texi | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/doc/lispref/customize.texi b/doc/lispref/customize.texi
index 2a72276bc5..fcfc0d297e 100644
--- a/doc/lispref/customize.texi
+++ b/doc/lispref/customize.texi
@@ -358,6 +358,10 @@ Variable Definitions
 @code{hook}, @code{plist} and @code{alist}.  See the definition of the
 individual types for a description of how to use @code{:options}.
 
+Re-evaluating a @code{defcustom} form with a different :options value
+does not clear the values added by previous evaluations, or by
+calls to @code{custom-add-frequent-value} (see below).
+
 @item :set @var{setfunction}
 @kindex set@r{, @code{defcustom} keyword}
 Specify @var{setfunction} as the way to change the value of this
@@ -485,6 +489,10 @@ Variable Definitions
 
 The precise effect of adding a value depends on the customization type
 of @var{symbol}.
+
+Since evaluating a @code{defcustom} form does not clear values added
+previously, Lisp programs can use this function to add values for user
+options not yet defined.
 @end defun
 
 Internally, @code{defcustom} uses the symbol property
-- 
2.28.0