bug#69270: 29.1; transient.el: Using `transient-define-prefix' with a lambda command results in warning

[Eli Zaretskii <eliz@gnu.org>]

> From: Fadi Moukayed <smfadi@gmail.com>
> Date: Mon, 19 Feb 2024 11:45:25 +0100
> 
> Mentioned on the #emacs channel (libera).
> 
> As per https://www.gnu.org/software/emacs/manual/html_mono/transient.html#Suffix-Specifications
> – it is mentioned that "COMMAND can also be a lambda expression."
> 
> However, evaluating the form (even on an Emacs instance started with "emacs -Q")
> 
>   (transient-define-prefix my-test-transient () ["Heading" ("a"
> "choice a" (lambda () (interactive)))])
> 
> Results in the following warning being printed on the *Messages* buffer:
> 
>   Warning: (lambda nil \...) quoted with ' rather than with #'
> 
> Attempting to hashquote the lambda as in:
> 
>   (transient-define-prefix my-test-transient () ["Heading" ("a"
> "choice a" (lambda () (interactive)))])
> 
> ... as suggested by some on #emacs results in an error when evaluating.
> 
> At this point, I am not sure if this is an error in documentation of
> transient.el, or an error in the macro definition of the
> `transient-define-prefix' macro itself, or if the warning is
> superfluous and whether it should be ignored. As I'm unsure whether
> this is a bug or not, I'm erring on the side of safety and reporting
> it to bring it to attention.

Jonas, could you please look into this?

Thanks.