Create a Feature Branch Approval Policy

Defines a policy for how new feature branches should be requested and
approved. We defer the management of feature branches to other future
policies.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Anton Arapov <anton@openssl.org>
(Merged from #62)

policies/feature-branch-approval-policy.md

@@ -0,0 +1,55 @@
+# Feature Branch Approval Policy
+
+The [Time-based Release Policy] defines a regular twice-a-year schedule for new
+OpenSSL versions. In the case of large features that cannot reasonably be
+implemented and reviewed within a single PR there is a risk that only an
+incomplete or incorrect implementation of the feature will be merged to the
+master branch by the time a feature freeze occurs for the next release.
+
+To avoid this problem feature branches can be used. A feature branch is simply
+a branch in the main git repository that can be used as a target branch for
+PRs related to a single new feature.
+
+A feature branch will be created based on the current state of master at the
+time of its creation. If a feature branch exists for a protracted period of time
+then it will need to be rebased on a regular basis. This process should be
+performed by a committer on an as-needed basis and can be done without further
+review.
+
+The creation of a new feature branch implies some overhead for the project to
+manage that feature branch (such as for example periodic rebases, and to review
+PRs targeting it). Such a feature branch would typically only be created where
+it has been agreed that the feature is desirable; exists on the [Project Board];
+is of sufficiently high priority; and there are expected to be resources
+available to work on the feature development and to review it. For this reason
+the creation of new feature branches is controlled via an approval process.
+
+Submitting a request for a new feature branch should be done by creating an
+issue in the [openssl/project] repository. Such a request can be created by
+anyone. The request should specify:
+
+- The name of the feature branch requested in the form of `feature/<name>`
+- A link to an issue describing the requested feature that will be developed on
+  the branch
+- An estimate of when the work on the feature is expected to be complete
+- Whether there are any known resources being made available to work on the
+  feature
+
+The approval of a new feature branch is ultimately performed by the OMC. The OMC
+may delegate the authority to make such approvals on its behalf to another body
+at the discretion of the OMC.
+
+Once approved by the OMC a feature branch may be created. All PRs relevant to
+that feature should target that branch and go through the normal code review
+process.
+
+Once the feature is complete and all relevant PRs have been merged to the branch,
+a PR should be created containing all the commits from the branch. All of the
+commits should already have been reviewed before they were pushed to the
+feature branch. However this PR review stage enables a final check to confirm
+the complete feature is sane. Once this PR is merged, the feature branch should
+then be deleted from the repository.
+
+[Time-based Release Policy]: https://github.com/openssl/general-policies/blob/master/policies/release-policy.md
+[Project Board]: https://github.com/orgs/openssl/projects/2/views/28
+[openssl/project]: https://github.com/openssl/project