bug#73722: 30.0.91; error calling eshell/clear with no argument

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 15 Oct 2024 14:31:21 -0700
> Cc: christopher@librehacker.com, 73722@debbugs.gnu.org
> From: Jim Porter <jporterbugs@gmail.com>
> 
> On 10/15/2024 11:04 AM, Eli Zaretskii wrote:
> >> Eli, does this look ok for the release branch? It fixes a regression
> >> from Emacs 29 and adds a pair of regression tests to prevent future
> >> breakage. (If and when this merges, I'll see about a more-thorough fix
> >> for the master branch too.)
> > 
> > If the problem is with empty body of progn, why does the fix have to
> > be so much less self-evident?  Can you fix it by protecting against
> > empty body of progn instead, so that the fix is less likely to cause
> > unintended consequences?
> 
> That's just the loudest part of the bug. Even though I've already fixed 
> that part on Emacs 31, things still don't work correctly there. If you 
> run the "clear" command in Eshell it clears the screen, but then prints 
> two new prompts on the same line together. However, this behavior is 
> pretty close to what "clear" did in Emacs 29: it prints two prompts (but 
> there's a newline between them).
> 
> If I fix the empty 'progn' case, I guess that would fix the regression 
> (aside from the missing newline, which I'm not sure how to fix). 
> However, "clear" still wouldn't work correctly.
> 
> What do you think would be better for Emacs 30? Fix "clear" so it works 
> properly, or just fix the new regression? (In the latter case, I can fix 
> it with a one-liner.)

At this late stage, I prefer the latter, yes.