Re: [RFC PATCH] vreportf: ensure sensible ordering of normal and error output

[Jeff King <peff@peff.net>]

On Tue, Nov 30, 2021 at 09:05:54AM -0500, Eric Sunshine wrote:

> >   - shouldn't status messages like this go to stderr anyway? I know some
> >     people follow the "unless it is an error, it should not to go
> >     stderr" philosophy. But I think in general our approach in Git is
> >     more "if it is the main output of the program, it goes to stdout; if
> >     it is chatter or progress for the user, it goes to stderr".
> 
> I considered this as well and agree that it would be a nicer localized
> fix, but...
> 
> (1) I don't think the practice is documented anywhere, so people --
> including me when I wrote builtin/worktree.c -- might not know about
> it. Indeed, we don't seem to be entirely consistent about doing it
> this way. Randomly picking submodule-helper.c, for instance, I see
> status-like messages going to stdout:
> 
>     printf(_("Entering '%s'\n"), displaypath);
>     printf(_("Synchronizing submodule url for '%s'\n"), ...);
> 
>     if (...)
>         format = _("Cleared directory '%s'\n");
>     else
>         format = _("Could not remove submodule work tree '%s'\n");
>     printf(format, displaypath);

Yeah, we've definitely not been consistent here. There's no silver
bullet for this aside from vigilance during review, but probably laying
out guidelines could help.

Here's a past discussion (that actually goes the other way: somebody
complaining that stderr should be on stdout!) where I laid out my mental
model:

  https://lore.kernel.org/git/20110907215716.GJ13364@sigill.intra.peff.net/

> (2) With git-worktree being four or five years old, for
> backward-compatibility concerns, I worry that "that ship has sailed",
> where 'that' is the freedom to relocate those status-like messages
> from stdout to stderr. I don't want to break tooling which exists
> around git-worktree.

IMHO it would be OK to change these. They are, after all, marked for
translation, so they're not reliably machine-readable anyway. It's
possible that some script could not be parsing them, but just trying to
redirect them. Or even keying on content in stderr as a sign of an error
(as tcl likes to do). But I don't think that's a guarantee we want to be
bound by.

See 68b939b2f0 (clone: send diagnostic messages to stderr, 2013-09-18)
for a similar case in the past.

> I'd be happy to be wrong on the second point -- indeed, git-worktree
> is still marked "experimental" in the man-page, but that may not mean
> anything this late in the game -- and submit a patch which places
> git-worktree's status-like messages on stderr instead of stdout.
> Thoughts?

I'm in favor. :)

-Peff