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

[Eric Sunshine <sunshine@sunshineco.com>]

On Tue, Nov 30, 2021 at 3:47 PM Jeff King <peff@peff.net> wrote:
> On Tue, Nov 30, 2021 at 09:05:54AM -0500, Eric Sunshine wrote:
> > (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:
>
> 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/

Thanks for the reference. I'll take a stab at adding a blurb about
this to CodingGuidelines.

> > (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.

That's a good point about them being marked for translation. It also
reminds me that we made some reasonably significant changes to this
exact message in 2c27002a0a (worktree: improve message when creating a
new worktree, 2018-04-24), and we didn't hear any complaints, let
alone complaints about tool breakage.

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

Nice. This and the above make me feel much more comfortable with the
idea of changing git-worktree to send these sorts of messages to
stderr rather than stdout.

> > 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. :)

Thanks. I'll drop this RFC patch and resubmit with a patch which just
fixes git-worktree to be chatty on stderr instead of stdout.