For example, set a flag when user inserts a space character after a
non-space character. If he subsequently inserts a non space character,
insert a single space into the buffer.

Did you try it out in an emacs buffer? Really, give it a shot. The current
behavior is so counterintuitive as to make it useless.

On Tue, 8 Dec 2020, 19:25 Eli Zaretskii, <eliz@gnu.org> wrote:

> > From: David Klein <dklein0@gmail.com>
> > Date: Tue, 8 Dec 2020 19:13:33 +0200
> > Cc: 45116@debbugs.gnu.org
> >
> > If I typed in the text
> >
> > "The quick brown
> >
> > jumped
> >
> > over
> > "
> >
> > and then went up to the end of the first line and type the characters
> > '[space]' 'H' 'e' 'l' 'l' 'o'
> >
> > I get
> >
> > "The quick brownHello"
> >
> > instead of
> >
> > "The quick brown Hello"
> >
> > i.e. zero spaces instead of one. Only excess whitespace should be removed
> > and the first space isn't excess.
>
> What logic would you suggest to implement to decide that this space is
> it not excess?
>