Re: carriage-return no longer works quite right in shell-mode

[Stefan Monnier <monnier@iro.umontreal.ca>]

> I recently updated Emacs from the CVS trunk and one of the programs
> I run inside a shell-mode buffer has stopped formatting its
> output correctly.

How old was your previous Emacs?

> It uses carriage return characters to re-write the same line over and
> over, and leaves the cursor at the beginning of the line.  Here's a
> simplified example that no longer works in Emacs:

> #include <stdio.h>
> main() {
>   int i;
>   for (i = 0; i < 10; i++) {
>     printf("  count: %d\r", i);
>     fflush(stdout);
>     sleep(1);
>   }
>   printf("\n");
> }

> Instead of re-writing the same part of the buffer over and over, I see:
>     count: 0  count: 1  count: 2
> in the buffer - the carriage return isn't returning the carriage like
> it used to.

Hmm... I see that indeed.

> I notice that apt-get does still work - that leaves the cursor at the
> end of the line, which I guess is the important difference.

Yes.  Funnily enough, in Emacs-22 the two behave identically because
when your program sends "count: N\r", Emacs passes the "count: N" to the
`shell' package, but keeps the \r for later because it needs to first
see if the following char is a \n or not in order to know whether to
drop the \r or not.  I.e. the details of decoding DOS-style EOLs caused
Emacs to turn one form into the other.

So it indeed, looks like a problem introduced by the unicode merge: for
some reason, the unicode code just sends the \r eagerly before it can
tell whether the next char is a \n.
I'll keep it in my todo list, but it may take me a little while to get
back to it, so if someone wants to do it before, he's welcome,


        Stefan