[RFC PATCH v2] docs: document upcoming breaking changes

Over time, Git has grown quite a lot. With this evolution, many ideas that were sensible at the time they were introduced are not anymore and are thus considered to be deprecated. And while some deprecations may be noted in manpages, most of them are actually deprecated in the "hive mind" of the Git community, only.

Introduce a new document that lists upcoming breaking changes, but also deprecations which we are not willing to go through with, to address this issue. This document serves multiple purposes:

  - It is a way to facilitate discussion around proposed deprecations.

  - It allows users to learn about deprecations and speak up in case
    they have good reasons why a certain feature should not be
    deprecated.

  - It states intent and documents where the Git project wants to go,
    both in the case where we want to deprecate, but also in the case
    where we don't want to deprecate a specific feature.

The document is _not_ intended to cast every single discussion into stone. It is supposed to be a living document that may change over time when there are good reasons for it to change.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---

I have tried to accommodate for all feedback to v1. Most notably:

  - I have introduced a new section that documents concepts that are
    _not_ to be deprecated. The intent is to capture discussions around
    proposed deprecations where we ultimately decide that we do not
    (yet) want to deprecate it.

  - I have added some more proposed deprecations. As before, all of this
    is up for discussion and I do not want to force any of the proposed
    deprecations onto anybody.

  - I have dropped the "$GITDIR/hooks" deprecation item for now. It is
    premature to have it at this point in time given that the
    config-based approach isn't even close to landing.

Patrick

Range-diff against v1:
1:  a78d68ecc2 ! 1:  2ef53ff98b docs: document upcoming breaking changes
    @@ Commit message
         noted in manpages, most of them are actually deprecated in the "hive
         mind" of the Git community, only.
     
    -    Introduce a new document that lists upcoming breaking changes to address
    +    Introduce a new document that lists upcoming breaking changes, but also
    +    deprecations which we are not willing to go through with, to address
         this issue. This document serves multiple purposes:
     
           - It is a way to facilitate discussion around proposed deprecations.
    @@ Commit message
             they have good reasons why a certain feature should not be
             deprecated.
     
    -      - It states intent and documents where the Git project wants to go.
    +      - It states intent and documents where the Git project wants to go,
    +        both in the case where we want to deprecate, but also in the case
    +        where we don't want to deprecate a specific feature.
     
         The document is _not_ intended to cast every single discussion into
         stone. It is supposed to be a living document that may change over time
    @@ Documentation/UpcomingBreakingChanges.md (new)
     @@
     +# 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.
    ++
    ++The Git project will thus irregularly release major 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 major versions is typically measured in multiple years.
    ++
     +The intent of this document is to track upcoming deprecations for the next major
    -+Git release. It is supposed to be a living document where proposed changes and
    ++Git release. Furthermore, this document also tracks what will _not_ be
    ++deprecated. This is done such that the outcome of discussions documente both
    ++when the discussion favors deprecation, but also when it rejects a deprecation.
    ++
    ++It is supposed to be a living document where proposed changes and
     +deprecations are up for discussion.
     +
     +## Git 3.0
    @@ Documentation/UpcomingBreakingChanges.md (new)
     +
     +### Removals
     +
    -+ - git-config(1) has learned to use subcommands that replace implicit actions
    -+   (e.g. `git config foo.bar baz`) as well as the action flags (e.g. `git config
    -+   --unset-all`). The actions will be removed in favor of subcommands.
    -+   Prerequisite for this change is that the new subcommands have been out for at
    -+   least for two years to give script authors time to migrate.
    -+
    -+   Cf. <ZjiL7vu5kCVwpsLd@tanuki>.
    -+
     + - git-http-push(1) can be used to push objects to a remote repository via
     +   HTTP/DAV. Support for write support via WebDAV is not in widespread use
     +   nowadays anymore and will be removed together with the command.
    @@ Documentation/UpcomingBreakingChanges.md (new)
     +   shorthands for URLs for git-fetch(1), git-pull(1) and git-push(1). This
     +   concept has long been replaced by remotes and will thus be removed.
     +
    -+ - git-annotate(1) is an alias for git-blame(1) with the `-c` flag. It will
    -+   be removed in favor of git-blame(1).
    -+
     + - "gitweb" and git-instaweb(1) can be used to browse Git repositories via an
     +   HTTP server. These scripts have been unmaintained for a significant amount of
     +   time and will be removed.
    @@ Documentation/UpcomingBreakingChanges.md (new)
     +   very slow, hard to use and has many gotchas. It will thus be removed in favor
     +   of [git-filter-repo](https://github.com/newren/git-filter-repo).
     +
    -+ - githooks(5) can be installed by placing them into `$GIT_DIR/hooks/`. This has
    -+   been a source of multiple remote code execution vulnerabilities. The feature
    -+   will be removed in favor of `core.hooksDirectory` and the new config-based
    -+   hooks.
    ++ - The "dashed form", i.e. support for calling `git-<command>` instead of
    ++   `git <command>` in scripts, has been deprecated for a long time and will be
    ++   removed.
    ++
    ++ - The command to import patches from Quilt seems to be used rarely, if
    ++   ever, and will be removed.
    ++
    ++ - Support for importing repositories from GNU Arch will be removed because
    ++   it would not appear to have any users.
    ++
    ++ - Support for interacting with CVS repositories (via `cvsimport`,
    ++   `cvsexportcommit` and `cvsserver`) is of dubious use by now, judging by
    ++   the number of times these commands have been mentioned recently. The
    ++   code has been essentially unmaintained, too, and will be removed.
    ++
    ++ - Support for grafting commits has long been superseded by git-replace(1).
    ++   Grafts are inferior to replacement refs as the mechanism can lead to
    ++   hard-to-diagnose problems when transferring objects between repositories.
    ++   They have been outdated since e650d0643b (docs: mark info/grafts as outdated,
    ++   2014-03-05) and will be removed.
    ++
    ++## 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 superseded features.
    ++
    ++ - git-annotate(1) is an alias for git-blame(1) with the `-c` flag. As
    ++   the maintenance burden of carrying both of these commands is negligible, both
    ++   commands will stay.
    ++
    ++ - git-restore(1) and git-switch(1) have been introduced as a replacement for
    ++   git-checkout(1). As git-checkout(1) is quite established, and as the benefit
    ++   of switching to git-restore(1) and git-switch(1) is contended, all three
    ++   commands will stay.
    ++
    ++ - git-config(1) has learned to use subcommands that replace implicit actions
    ++   (e.g. `git config foo.bar baz`) as well as the action flags (e.g. `git config
    ++   --unset-all`). The action flags will not be removed in the next major Git
    ++   release as there likely exist a lot of scripts out there that use the old
    ++   syntax.
    ++
    ++   Cf. <ZjiL7vu5kCVwpsLd@tanuki>.

 Documentation/UpcomingBreakingChanges.md | 119 +++++++++++++++++++++++
 1 file changed, 119 insertions(+)
 create mode 100644 Documentation/UpcomingBreakingChanges.md