= Upcoming breaking changes The Git project aims to ensure backwards compatibility to the best extent possible. Minor releases will not break backwards compatibility unless there is a very strong reason to do so, like for example a security vulnerability. Regardless of that, due to the age of the Git project, it is only natural to accumulate a backlog of backwards-incompatible changes that will eventually be required to keep the project aligned with a changing world. These changes fall into several categories: * Changes to long established defaults. * Concepts that have been replaced with a superior design. * Concepts, commands, configuration or options that have been lacking in major ways and that cannot be fixed and which will thus be removed without any replacement. Explicitly not included in this list are fixes to minor bugs that may cause a change in user-visible behavior. The Git project irregularly releases breaking versions that deliberately break backwards compatibility with older versions. This is done to ensure that Git remains relevant, safe and maintainable going forward. The release cadence of breaking versions is typically measured in multiple years. We had the following major breaking releases in the past: * Git 1.6.0, released in August 2008. * Git 2.0, released in May 2014. We use . release numbers these days, starting from Git 2.0. For future releases, our plan is to increment in the release number when we make the next breaking release. Before Git 2.0, the release numbers were 1.. with the intention to increment for "usual" breaking releases, reserving the jump to Git 2.0 for really large backward-compatibility breaking changes. The intent of this document is to track upcoming deprecations for future breaking releases. Furthermore, this document also tracks what will _not_ be deprecated. This is done such that the outcome of discussions document both when the discussion favors deprecation, but also when it rejects a deprecation. Items should have a clear summary of the reasons why we do or do not want to make the described change that can be easily understood without having to read the mailing list discussions. If there are alternatives to the changed feature, those alternatives should be pointed out to our users. All items should be accompanied by references to relevant mailing list threads where the deprecation was discussed. These references use message-IDs, which can visited via https://lore.kernel.org/git/$message_id/ to see the message and its surrounding discussion. Such a reference is there to make it easier for you to find how the project reached consensus on the described item back then. This is a living document as the environment surrounding the project changes over time. If circumstances change, an earlier decision to deprecate or change something may need to be revisited from time to time. So do not take items on this list to mean "it is settled, do not waste our time bringing it up again". == Git 3.0 The following subsections document upcoming breaking changes for Git 3.0. There is no planned release date for this breaking version yet. Proposed changes and removals only include items which are "ready" to be done. In other words, this is not supposed to be a wishlist of features that should be changed to or replaced in case the alternative was implemented already. === Changes * The default hash function for new repositories will be changed from "sha1" to "sha256". SHA-1 has been deprecated by NIST in 2011 and is nowadays recommended against in FIPS 140-2 and similar certifications. Furthermore, there are practical attacks on SHA-1 that weaken its cryptographic properties: + ** The SHAppening (2015). The first demonstration of a practical attack against SHA-1 with 2^57 operations. ** SHAttered (2017). Generation of two valid PDF files with 2^63 operations. ** Birthday-Near-Collision (2019). This attack allows for chosen prefix attacks with 2^68 operations. ** Shambles (2020). This attack allows for chosen prefix attacks with 2^63 operations. + While we have protections in place against known attacks, it is expected that more attacks against SHA-1 will be found by future research. Paired with the ever-growing capability of hardware, it is only a matter of time before SHA-1 will be considered broken completely. We want to be prepared and will thus change the default hash algorithm to "sha256" for newly initialized repositories. + An important requirement for this change is that the ecosystem is ready to support the "sha256" object format. This includes popular Git libraries, applications and forges. + There is no plan to deprecate the "sha1" object format at this point in time. + Cf. <2f5de416-04ba-c23d-1e0b-83bb655829a7@zombino.com>, <20170223155046.e7nxivfwqqoprsqj@LykOS.localdomain>, . === Removals * Support for grafting commits has long been superseded by git-replace(1). Grafts are inferior to replacement refs: + ** Grafts are a local-only mechanism and cannot be shared across repositories. ** Grafts can lead to hard-to-diagnose problems when transferring objects between repositories. + The grafting mechanism has been marked as outdated since e650d0643b (docs: mark info/grafts as outdated, 2014-03-05) and will be removed. + Cf. <20140304174806.GA11561@sigill.intra.peff.net>. == Superseded features that will not be deprecated Some features have gained newer replacements that aim to improve the design in certain ways. The fact that there is a replacement does not automatically mean that the old way of doing things will eventually be removed. This section tracks those features with newer alternatives. * The features git-checkout(1) offers are covered by the pair of commands git-restore(1) and git-switch(1). Because the use of git-checkout(1) is still widespread, and it is not expected that this will change anytime soon, all three commands will stay. + This decision may get revisited in case we ever figure out that there are almost no users of any of the commands anymore. + Cf. , , <112b6568912a6de6672bf5592c3a718e@manjaro.org>.