Re: [Patch] Add project.el command to replace symbol at point throughout project

[Dmitry Gutov <dgutov@yandex.ru>]

On 16.01.2022 19:58, Juri Linkov wrote:
>>> This is needed to handle `read-regexp` in `occur-read-primary-args`
>>> that uses the symbol `regexp-history-last` by default.
>>
>> occur?
>>
>> read-regexp is called from query-replace-read-from.
>>
>> Binding read-regexp-defaults-function doesn't seem to work because its use
>> is for some reason predicated on (and defaults (symbolp defaults))
>> evaluating to non-nil.
>>
>> And 'read-regexp' is called with nil second argument.
> 
> The customizable user option 'read-regexp-defaults-function' was created
> for the following problem: by default, 'occur' uses the last history item
> as the default value, so 'read-regexp-defaults-function' could be
> customized to get a tag at point as the default value of 'occur'.
> 
> Exactly the same situation is with 'query-replace-read-from':
> by default, it uses the last history item, so changing the value of
> 'read-regexp-defaults-function' should also affect the query-replace
> like in the patch that I sent to Jon.

The patch works for project-query-replace-regexp but not for 
xref-find-references-and-replace, which still doesn't suggest the symbol 
at point as FROM (BTW, in the final version this function should 
probably use #'find-tag-default rather than 'find-tag-default-as-regexp).

>>> Before finishing this implementation, please answer one question.
>>> `query-replace-read-from` uses two minibuffer-reading functions:
>>>                   (if regexp-flag
>>>                       (read-regexp prompt sym-at-point 'minibuffer-history)
>>>                     (read-from-minibuffer
>>>                      prompt nil nil nil nil
>>>                      (query-replace-read-from-suggestions) t))
>>> Do you think the same default with the symbol at point
>>> should be used for the non-regexp case with read-from-minibuffer as well?
>>> If yes, then we need a different solution that works for both cases.
>>
>> It doesn't have to be the same. project-query-replace-regexp could bind
>> read-regexp-defaults-function, and xref-find-references-and-replace could
>> bind something else. But that variable still needs to be created.
> 
> xref-find-references-and-replace calls query-replace-read-args
> with a non-regexp flag, so I have no idea what new variable
> could be created for read-from-minibuffer.

I don't really have a preference as to how the implementation is 
organized, as long as it all works.

As far as I'm concerned, it might as well use 
read-regexp-defaults-function. But the implementation is made more 
complicated by the fact that read-regexp and read-from-minibuffer treat 
their PROMPT and DEFAULTS arguments differently.

E.g. the latter won't return DEFAULT-VALUE on empty input and won't 
format the prompt. If I use read-string instead, it uses the default 
value instead of empty input, but does not format the prompt still.

> It already uses
> 'query-replace-read-from-suggestions' where the top value
> could be the default.

That would affect all callers of query-replace-read-from, wouldn't it? 
I'm not sure, but a conservative approach (which we often take here) 
would be to try to avoid that.