Re: [PATCH v2.5 2/2] tag: prevent nested tags

From: Denton Liu <liu.denton@gmail.com>
Date: Apr 3, 2019, 21:33 UTC
Message-ID: <20190403213318.GA14137@dev-l>
In-Reply-To: <xmqqzhp7sfw4.fsf@gitster-ct.c.googlers.com>

On Wed, Apr 03, 2019 at 04:32:27PM +0900, Junio C Hamano wrote:

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> Denton Liu <liu.denton@gmail.com> writes:
> 
> > This is the first use of the '%n$<fmt>' style of printf format in the
> > *.[ch] files in our codebase, but it's supported by POSIX[1] and there
> > are existing uses for it in po/*.po files, so hopefully it won't cause
> 
> The latter is a stronger indication that this should be OK than the
> former ;-)  Thanks for digging and noting.

Thank Ævar, I shamelessly stole this message from one of his patches that didn't get included in[1].

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> 
> > diff --git a/Documentation/config/advice.txt b/Documentation/config/advice.txt
> > index 88620429ea..ec4f6ae658 100644
> > --- a/Documentation/config/advice.txt
> > +++ b/Documentation/config/advice.txt
> > @@ -90,4 +90,6 @@ advice.*::
> >  	waitingForEditor::
> >  		Print a message to the terminal whenever Git is waiting for
> >  		editor input from the user.
> > +	nestedTag::
> > +		Advice shown if a user attempts to recursively tag a tag object.
> >  --
> 
> In addition to 'advice', we may have to add a configuration to help
> projects that wants to tag tag objects regularly so that they do not
> have to keep typing "--allow-nested-tag".  But that can wait until a
> participant of such a project comes forward and makes a case for
> their workflow.
> 
> > +chain of custody by signing someone else's signed tag. However, in
> > +practice, this is typically a mistake so we prevent it from happening by
> > +default unless specifically requested.
> 
> I am not sure if this is so bad, actually.  Why do we need to treat
> it as a mistake?  When a command that wants a commit is fed a tag
> (either a tag that directly refers to a commit, or a tag that tags
> another tag that refers to a commit), the command knows how to peel
> so it's not like the user is forced to say "git log T^{commit}".

This patch came about because Robert Dailey expressed confusion after accidentally creating a tag-to-a-tag a while back by mistake when he actually meant to amend a tag.

In the discussion upthread, Peff noted that he has never seen a tag-to-a-tag in the wild before. I think the conclusion was that for the majority of users, doing this is an error. That is what this patch is guarding against.

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> 
> And if something that *MUST* take a commit refuses to (or more
> likely, forges to) peel a tag down to a commit and yields an error,
> I think that is what needs fixing, not the command that creates a
> tag.
> 
> So, I am fairly negative on this change---unless it is made much
> more clear in the doc and/or in the proposed log message what
> practical downside there are to the end users if we do not stop this
> "mistake", that is.

I can update the log message to include more detail.

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> 
> > +Automatically erroring on nested tags was introduced in Git version
> > +2.22.0.
> 
> And please do not write something like this.  A feature gets in a
> release when it is ready, and we may not ship this in 2.22.

Ævar suggested that we include this because git tag gets used by a lot of scripts so in case one ever starts failing, a maintainer can more easily track down the reason why.

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> 
> "git tag --help" the user is running may or may not have the
> paragraph about "nested tag", depending on the existence of the
> feature in the version of Git the user is running, so there is no
> need to say something like that.
> 
> And no, I do not buy arguments like "random web servers serve
> different versions of documentation without identifying which
> version of Git they describe".
>

Thanks for the comments,

Denton

[1]: https://public-inbox.org/git/20181026192734.9609-8-avarab@gmail.com/