Re: cl-defgeneric vs random funcall in project.el

[Dmitry Gutov <dgutov@yandex.ru>]

On 07/28/2015 02:31 PM, Stephen Leake wrote:

> But the default method uses 'project-search-path-function', which
> elisp-mode sets to `elisp-search-function'; elisp.el does not use
> cl-defmethod to override project-search-path.

It's largely because, currently, project-search-path is supposed to 
return the source directories inside the project, as well as outside. 
And if a project implementation has to provide its own implementation, 
it's much cleaner, I think, if it only has to deal with 
project-search-path-function, instead of being forced to 
cl-call-next-method.

Further, this part seems like it'd be impossible to implement: "A 
specialized implementation should use the value
`project-search-path-function', or, better yet, call and combine
the results from the functions that this value is set to by all
major modes used in the project".

However, now that we've reached the consensus that project-search-path 
doesn't need to include the directories inside the current project, an 
implementation will only need to override it if it actually knows 
search-path better than the major-mode.

> Why do we need both dispatching methods?

The alternative (which is more feasible now) is to use the context 
specializer, like:

(cl-defmethod project-search-path (_project &context (major-mode (eql 
emacs-lisp-mode))))

It's also undocumented yet, and the method dispatch priority between it 
and method implementation dispatching on the first argument is also 
unclear now.

And it'll need a separate declaration for each deriving mode (such as 
lisp-interaction-mode).

Opinions welcome.