Async-wait: selecting deleted buffer

[dieggsy]

The documentation for async-start says:

Note: Even when FINISH-FUNC is present, a future is still
returned except that it yields no value (since the value is
passed to FINISH-FUNC).  Call ‘async-get’ on such a future always
returns nil.  It can still be useful, however, as an argument to
‘async-ready’ or ‘async-wait’.

But I'm finding some errors when this is the case. As minimal examples:

(async-wait 
  (async-start 
    (lambda () (message "hello")) 
    'ignore))

and

(async-wait 
  (async-start 
    (lambda () (message "hello")) 
    (lambda (result) (message "this %s" result))))

Both return the error selecting deleted buffer.

[thierryvolpiatto]

Sorry for late reply.
Seems like the docstring of async-start is wrong or at least confusing.
async-wait is not really meant to be use alone, AFAIU it is an internal function which should be renamed with internal prefix i.e async--wait.
What you want to use here, I guess is async-get, which is meant to be used on a FUTURE (the result of an async-start call) called with a nil callback, e.g

(async-get 
 (async-start 
  (lambda () (message "hello") )
  nil))

And perhaps there is a bug here when it returns error "selecting deleted buffer" with a call like this:

(async-get 
 (async-start 
  (lambda () (message "hello") )
  'ignore))

@jwiegley WDYT

[thierryvolpiatto]

And I am wrong about async-wait which should not be internal as I said above, it is useful to as its name say to wait the FUTURE is ready to send its result:

(let ((proc (async-start 
             (lambda () (message "hello")))))
  (async-wait proc)
  (async-get proc))

[thierryvolpiatto]

@jwiegley can you clarify about async-wait usage ? Perhaps an example in the test file ?