From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pb-smtp2.pobox.com (pb-smtp2.pobox.com [64.147.108.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E9C7B26AC1 for ; Sun, 22 Sep 2024 17:51:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=64.147.108.71 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727027517; cv=none; b=WGiemixIgYYE6p7+ENyt77tZYPlImQ4tItd4abYmJq5B7My/IMorPUVHjAgc4IBHt/GT/O6eIqFPiitdUeoQ0wmMLRMPHE83fm9qf4NqJSKzkP+8utrPvL595ewc84/y7i7e/C7I/ZqPJqJ6HghQsd4BZy7rXAJE43S38VKxDkU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727027517; c=relaxed/simple; bh=HXi0Ponnilci+VPeoGHeH2Uu5YglEI4EJKPOERosHJA=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=k0PjawBi7dKX44XXXtLMdUkv1qppgE5tVlOvFOKuJJ5Q2zhOVPuLHf+/2esQ4RjBmC2N1sfaDBxMMprlg7X0nyNZyB16+TP0ZlNi4Q73S+NwPWJQmni8WEHWhQhmTlBkmv+6VG3KFJhUSuibcZn0ZMs59l7ydRkXpcZoaC1ej+A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=pobox.com; spf=pass smtp.mailfrom=pobox.com; dkim=pass (1024-bit key) header.d=pobox.com header.i=@pobox.com header.b=v/hS815R; arc=none smtp.client-ip=64.147.108.71 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=pobox.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pobox.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=pobox.com header.i=@pobox.com header.b="v/hS815R" Received: from pb-smtp2.pobox.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id B47433DF61; Sun, 22 Sep 2024 13:51:54 -0400 (EDT) (envelope-from gitster@pobox.com) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed; d=pobox.com; h=from:to:cc :subject:in-reply-to:references:date:message-id:mime-version :content-type; s=sasl; bh=HXi0Ponnilci+VPeoGHeH2Uu5YglEI4EJKPOER osHJA=; b=v/hS815Rf8XUkzuF/SiBwNK6LqFZ1TyIp9O1M1/xQ+nscZwZsEPtCX yJc+Nz8HFPmSVSwuDmxDAFSH0Yg/3D4lmGIgLe6i/Vy2QQ/CVq9Rgi6fNitB999n Hcd0MJG+cTqQcFO9PQnTFenvd7re3BMTDzuizial+70VR3fy5hP6g= Received: from pb-smtp2.nyi.icgroup.com (unknown [127.0.0.1]) by pb-smtp2.pobox.com (Postfix) with ESMTP id AC9DB3DF60; Sun, 22 Sep 2024 13:51:54 -0400 (EDT) (envelope-from gitster@pobox.com) Received: from pobox.com (unknown [34.125.108.217]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by pb-smtp2.pobox.com (Postfix) with ESMTPSA id 0F5A13DF5F; Sun, 22 Sep 2024 13:51:53 -0400 (EDT) (envelope-from gitster@pobox.com) From: Junio C Hamano To: git@vger.kernel.org Cc: Patrick Steinhardt , Derrick Stolee , Jonathan Nieder , Emily Shaffer Subject: Re: [PATCH] BreakingChanges: early adopter option In-Reply-To: (Junio C. Hamano's message of "Fri, 20 Sep 2024 14:33:52 -0700") References: Date: Sun, 22 Sep 2024 10:51:52 -0700 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: git@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain X-Pobox-Relay-ID: 5A71CDE6-790B-11EF-8CE5-9B0F950A682E-77302942!pb-smtp2.pobox.com Junio C Hamano writes: > Junio C Hamano writes: > >> Discussing the desire to make breaking changes, declaring that >> breaking changes are made at a certain version boundary, and >> recording these decisions in this document, are necessary but not >> sufficient. We need to make sure that we can implement, test, and >> deploy such impactful changes. >> >> Formalize the mechanism based on the `feature.*` configuration >> variable to allow early adopters to opt into the breaking change in >> a version of Git before the planned version for the breaking change. >> ... > ... to see what it involves > to allow early adopters to experience Git 3.0 features/removals > before it actually happens. Sorry for a long monologue on this important topic, while everybody is away. Hopefully we'll see more comments when they get back once the week starts ;-) > Switching behaviour at runtime with feature.git3 should work well, > and we can also add tests that checks the new behaviour by doing > "test_config feature.git3 true". > ... > If we are willing to burden early adopters a bit more, we could make > it a build-time option. With "make GIT_BUILD_FOR_GIT3=YesPlease", > binaries will be built for all the then-current Git 3.0 features and > documentation under development. It certainly is a simpler-to-build > option that is easier for us, but I am not sure if that is acceptable > by those who volunteer to test the upcoming big version. > > One thing to note is that depending on the nature of a change, once > you start using a feature only available in a newer version of Git > in your repository, the resulting repository may not be understood > by an older version of Git... While I still am with the position that we can do this either at runtime or at build time, with the trade-off being that it is more costly for developers to do it at runtime and more cumbersome for early adopters to do it at build time, I realize that the last point above is unrelated. If one or some of the features behind either feature.git3 runtime option or GIT_BUILD_FOR_GIT3 build-time option makes a repository inaccessible to versions of Git without these features, we have the extension.* mechanism to make sure nothing breaks, and testing that such a Git3 feature is properly protected by the extension.* mechanism is part of the early adopter testing. How much more costly to do at runtime is still subject to further analysis, I think. I know that it means we need to build and install the docs twice to support "git -c feature.git3=on help", for example, but I am not sure what the best way to use CI would be (write tests that check features with different behaviour by explicitly running them with "git -c feature.git3=on"? Run the same set of tests in a separate job that has "[feature] git3" in its $HOME/.gitconfig?).