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From:   Junio C Hamano <gitster@pobox.com>
To:     Han-Wen Nienhuys <hanwenn@gmail.com>
Cc:     Han-Wen Nienhuys via GitGitGadget <gitgitgadget@gmail.com>,
        git@vger.kernel.org
Subject: Re: [PATCH v6 0/5] Reftable support git-core
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Date:   Wed, 19 Feb 2020 12:09:00 -0800
In-Reply-To: <CAOw_e7YPzLb-zR+NVCR=-cNJg_43Q0E758RBJubqDdgYR=tNww@mail.gmail.com>
        (Han-Wen Nienhuys's message of "Wed, 19 Feb 2020 20:14:35 +0100")
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Han-Wen Nienhuys <hanwenn@gmail.com> writes:

> On Wed, Feb 19, 2020 at 7:10 PM Junio C Hamano <gitster@pobox.com> wrote:
>> It is OK (and indeed you're right that you cannot avoid it) to ship
>> a reasonably new snapshot as a fallback in such a case, but it still
>> is far more preferrable to avoid linking with the fallback snapshot
>> copy when a working one is available on the system, especially for a
>> widely used and established library like zlib, because we have one
>> less thing to keep up-to-date with the security patches made to the
>> upstream.
>
> what is the procedure for doing this? Do I need to write autoconf
> macros (oh no!) ?

We treat the Makefile macros listed at the top of the file as
authoritative set of knobs, so 

    # Define ZLIB_LACKS_UNCOMPRESS2 if your zlib is so old to lack the
    # function uncompress2().

with conditional compilation/linkage based on the macro would be
minimally sufficient.  Setting it automatically in ./configure is
nice-to-have but is optional.