From: Kristoffer Haugsbakk <code@khaugsbakk.name>
Date: Tue, 16 Sep 2025 20:47:58 GMT
Subject: Re: [PATCH v5 0/8] you-still-use-that??: improve breaking changes troubleshooting
Message-ID: <e4fc3b83-15ca-4844-92c6-1f41169161ed@app.fastmail.com>
In-Reply-To: <xmqqy0qffrri.fsf@gitster.g>

On Mon, Sep 15, 2025, at 21:19, Junio C Hamano wrote:
> kristofferhaugsbakk@fastmail.com writes:
>
>> § Changes in v5
>>
>> Fix the leak that Peff found (with Peff’s suggestion).  Also fix (with
>> Peff’s help) a regression where you were able to get into an infinite
>> alias loop specifically when using deprecated builtin names.
>
> When merged to 'seen' and run with WITH_BREAKING_CHANGES=YesPlease,
> looping alias test would chage the behaviour, and the test needs to
> be prepared for it, I think.  Here is how t0014 fails
>
> expecting success of 0014.4 'looping aliases - deprecated builtins':
>         test_config alias.whatchanged pack-redundant &&
>         test_config alias.pack-redundant whatchanged &&
>         cat >expect <<-EOF &&
>         ${SQ}whatchanged${SQ} is aliased to ${SQ}pack-redundant${SQ}
>         ${SQ}pack-redundant${SQ} is aliased to ${SQ}whatchanged${SQ}
>         ${SQ}whatchanged${SQ} is aliased to ${SQ}pack-redundant${SQ}
>         fatal: alias loop detected: expansion of ${SQ}whatchanged${SQ}
> does not terminate:
>           whatchanged <==
>           pack-redundant ==>
>         EOF
>         test_must_fail git whatchanged -h 2>actual &&
>         test_cmp expect actual
>
> --- expect      2025-09-15 19:16:26.340366359 +0000
> +++ actual      2025-09-15 19:16:26.360366313 +0000
> @@ -1,6 +1 @@
> -'whatchanged' is aliased to 'pack-redundant'
> -'pack-redundant' is aliased to 'whatchanged'
> -'whatchanged' is aliased to 'pack-redundant'
> -fatal: alias loop detected: expansion of 'whatchanged' does not terminate:
> -  whatchanged <==
> -  pack-redundant ==>
> +fatal: cannot handle whatchanged as a builtin
> not ok 4 - looping aliases - deprecated builtins

Thanks.  This is (maybe you surmise or know already but) a
problem when on the branch itself as well.  I did some compiling
`WITH_BREAKING_CHANGES=YesPlease` and it seems that 07572f220a8
(whatchanged: remove when built with WITH_BREAKING_CHANGES, 2025-05-12)
made it a hard error to call `whatchanged` after its death:

    $ ./bin-wrappers/git whatchanged
    fatal: cannot handle whatchanged as a builtin

This seems fine, although I would have expected it to say something more
neutral like “command not found”.

What I don’t understand though is this:

    $ ./bin-wrappers/git -c alias.whatchanged=status whatchanged
    fatal: cannot handle whatchanged as a builtin

People have been saying that people can at least alias `whatchanged` to
`log <something>` and then it will work after the removal.  But now that
it has been removed (according to the commit message) its spirit lives
on and prevents reusing the name?

Am I missing something here?