RE: misleading message printed when worktree add fails

[<rsbecker@nexbridge.com>]

On November 28, 2021 12:01 PM, Eric Sunshine wrote:
> On Sun, Nov 28, 2021 at 11:47 AM Baruch Burstein <bmburstein@gmail.com>
> wrote:
> > > When I perform these actions, I see a "fatal error" message which
> > > clearly indicates failure, not success:
> > >
> > >     % git worktree add ../foo bar
> > >     Preparing worktree (checking out 'bar')
> > >     fatal: 'bar' is already checked out at '.../wherever'
> >
> > I see them in the other order:
> >
> >     fatal: 'master' is already checked out at 'C:/Users/bmbur/temp'
> >     Preparing worktree (checking out 'master')
> >
> > which I understood as "there was an error, but we managed to recover
> > somehow and set up the worktree anyway"
> 
> Okay, that's happening because the "Preparing" message is sent to stdout,
> whereas the "fatal" error is sent to stderr, and the streams are being flushed
> on Windows in a different order than what we typically see on Unix
> platforms even though the "Preparing" message is actually output first by the
> code.
> 
> A general fix (not specific to git-worktree) might be to have die() (or maybe
> vreportf()?) flush stdout before reporting the error message on stderr. That
> should make output order more predictable, such that general status
> messages appear before error messages.

This is probably a good idea. There is no guarantee even in Unix regarding stream buffer flushing. If there is a reason to sequence output between stdout and stderr, then fflush is important.

-Randall