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| author | Junio C Hamano <gitster@pobox.com> | 2024-06-20 15:45:16 -0700 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2024-06-20 15:45:16 -0700 |
| commit | 166cdd8915a957f0fb5a2bbca3075489e8e3a754 (patch) | |
| tree | 49730dcf834b97d85813964c82f752dd498ac8fd | |
| parent | 83ac567781b53f7101c2a9b44462df447bbdc2c6 (diff) | |
| parent | 028bb23a61653dde0481671a2ac4a4e83ce061b8 (diff) | |
| download | git-166cdd8915a957f0fb5a2bbca3075489e8e3a754.tar.gz | |
Merge branch 'ps/document-breaking-changes'
The structure of the document that records longer-term project
decisions to deprecate/remove/update various behaviour has been
outlined.
* ps/document-breaking-changes:
BreakingChanges: document that we do not plan to deprecate git-checkout
BreakingChanges: document removal of grafting
BreakingChanges: document upcoming change from "sha1" to "sha256"
docs: introduce document to announce breaking changes
| -rw-r--r-- | Documentation/BreakingChanges.txt | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/Documentation/BreakingChanges.txt b/Documentation/BreakingChanges.txt new file mode 100644 index 0000000000..0532bfcf7f --- /dev/null +++ b/Documentation/BreakingChanges.txt @@ -0,0 +1,135 @@ += 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 <major>.<minor> release numbers these days, starting from Git 2.0. For +future releases, our plan is to increment <major> in the release number when we +make the next breaking release. Before Git 2.0, the release numbers were +1.<major>.<minor> with the intention to increment <major> 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>, +<CA+EOSBncr=4a4d8n9xS4FNehyebpmX8JiUwCsXD47EQDE+DiUQ@mail.gmail.com>. + +=== 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. <xmqqttjazwwa.fsf@gitster.g>, +<xmqqleeubork.fsf@gitster.g>, +<112b6568912a6de6672bf5592c3a718e@manjaro.org>. |