Re: Calling eldoc-message directly

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> In that package, I use a server process to get information about the current
> buffer.  I can use it to asynchronously retrieve documentation about
> identifiers, among other things.  This pattern seems pretty common (I think
> that's how tide, elpy, cider, and multiple other modes work).

Indeed async use is currently not supported.

Not sure how to best add support for sync-processing.
Ideally, we'd pass a "continuation" to the eldoc-documentation-function,
but that would break existing functions which wouldn't expect that extra arg.

We could pass that extra arg via a dynamically-scoped variable like
`eldoc-continuation-function`.

An alternative would be to allow eldoc-documentation-function to return
a function, which is then called with the continuation.

So you'd do something like

    (defun my-eldoc-documentation-function (orig-fun)
      (if (not (my-determine-if-we-should-be-in-charge))
          (funcall orig-fun)
        (lambda (k)
          (let ((p (start-process ...)))
            (set-process-sentinel p
              (lambda (_p status)
                (funcall k (my-get-doc-string))))))))
    [...]
      (add-function :around (local 'eldoc-documentation-function)
                    #'my-eldoc-documentation-function)


-- Stefan