bug#69120: Spurious "function is not known to be defined" if defined in `use-package` body

[Konstantin Kharlamov]

On Wed, 2024-02-14 at 17:23 +0200, Eli Zaretskii wrote:
> > From: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> > Date: Wed, 14 Feb 2024 14:16:09 +0300
> > 
> > I have many functions that are only useful inside a specific mode.
> > So I
> > group them with `use-package`, by defining them inside `:init` or
> > `:config` section, depending on the use.
> > 
> > It turns out, byte-compiler does not consider such functions to be
> > defined and prints a warning about it.
> > 
> > # Steps to reproduce (in terms of terminal commands)
> > 
> >     λ cat test.el
> >     ;;; -*- lexical-binding: t -*-
> >     (use-package prog-mode
> >       :init
> >       (defun hello()
> >         (print "hello"))
> >       (hello))
> >     λ emacs -batch -f batch-byte-compile test.el
> > 
> >     In end of data:
> >     test.el:6:4: Warning: the function ‘hello’ is not known to be
> > defined.
> > 
> > ## Expected
> > 
> > File gets compiled with no warnings
> > 
> > ## Actual
> > 
> > There's a warning
> > 
> >     test.el:6:4: Warning: the function ‘hello’ is not known to be
> > defined.
> 
> What do you get if you macro-expand your code?

Wrapping the above code to a `(macroexpand …)` gives a:

   "hello"
   nil