bug#68570: 29.1; recompile might not re-use project-compile's buffer

[Dmitry Gutov <dmitry@gutov.dev>]

On 27/01/2024 19:53, Juri Linkov wrote:
>>> It's very useful to always create a unique buffer for every compilation:
>>> this allows keeping error messages from previous compilations.
>>
>> Hmm, but I suppose it can be a personal preference whether a "recompile"
>> should create a new buffer or not.
>>
>> Because it's also reasonable to expect that 'M-x compile' creates a new
>> buffer (e.g. project-prefixed and unique), but 'recompile', or
>> 'revert-buffer' - keep that buffer around and reuse it. When one wants to
>> keep the old contents, they could 'M-x compile' (or 'M-x project-compile')
>> instead.
>>
>> This might be my preference anyway, because OT1H old compilations are often
>> (but not always) handy to have around, OT2H I don't like to have too many
>> buffers, and the above distinction between 'compile' and 'recompile' would
>> be a tool to make that choice.
> 
> A new option could be added indeed.  But currently 'g' after 'compile'
> uses 'compilation-buffer-name-function' that can be configured
> to generate a new buffer.  So it's expected that 'g' after
> 'project-compile' should do the same and use
> 'project-compilation-buffer-name-function', especially
> when it's configured to generate a new buffer.

Again, I'm not sure if it's expected: even if I do like the idea of 
unique per-project compilation buffers, seeing 'g' reuse the existing 
buffer feels pretty natural.

> IOW, I think these two 'compile' and 'project-compile'
> should be in sync in regard to what 'recompile' does.

When I'm saying is that when 'recompile' reuses the current buffer it 
already follows the result of project-compilation-buffer-name-function 
(when it was invoked from project-compile, of course).

>>> I propose even to add such an option to the choice list in
>>> project-compilation-buffer-name-function, e.g.:
>>> (defcustom project-compilation-buffer-name-function nil
>>>     :type '(choice (const :tag "Default" nil)
>>>                    (const :tag "Prefixed with project name"
>>>                           project-prefixed-buffer-name)
>>>                    (const :tag "Prefixed and unique with project name"
>>>                           project-prefixed-unique-buffer-name)
>>>                    (function :tag "Custom function")))
>>
>> Sounds good.
> 
> There is also a proposal to add the same option
> to 'compilation-buffer-name-function' in bug#68697.

Sounds good to me. We could also ask the reporter there what they think 
'g' should do in such buffers (create a new one or reuse current).

>>> The previous patch would be needed as well since currently
>>> there is no way to allow unique project compilation buffers.
>>
>> The one in 0a07603ae8d?
> 
> Actually I meant https://debbugs.gnu.org/68570#23

We could make a new option in compile.el which would determine whether 
to do this in general: when non-nil, 'compilation-start' would save the 
current dynamic value of 'compilation-buffer-name-function', and 
'recompile' would call it again.

Otherwise the distinction remains that when 'recompile' is invoked 
inside a compilation buffer, the same buffer is used; and when it's 
invoked from some other buffer, a new compilation buffer can be created.