release: Add convenience script for branch cutting

Adds a convenience script to do branch cut to simplify the amount of
commands run in order to do the physical action of cutting the branch.

Also updates documentation related to branch cutting

Signed-off-by: Eli Uriegas <eliuriegas@fb.com>

Pull Request resolved: https://github.com/pytorch/pytorch/pull/72219
Approved by: https://github.com/malfet, https://github.com/atalman

RELEASE.md

@@ -4,6 +4,8 @@
 
   - [General Overview](#general-overview)
   - [Cutting release branches](#cutting-release-branches)
+    - [`pytorch/pytorch`](#pytorchpytorch)
+    - [`pytorch/builder` / PyTorch domain libraries](#pytorchbuilder--pytorch-domain-libraries)
     - [Making release branch specific changes](#making-release-branch-specific-changes)
     - [Getting CI signal on release branches:](#getting-ci-signal-on-release-branches)
   - [Drafting RCs (Release Candidates)](#drafting-rcs-release-candidates)
@@ -31,26 +33,35 @@ Releasing a new version of PyTorch generally entails 3 major steps:
 
 ## Cutting release branches
 
+### `pytorch/pytorch`
+
 Release branches are typically cut from the branch [`viable/strict`](https://github.com/pytorch/pytorch/tree/viable/strict) as to ensure that tests are passing on the release branch.
 
-Release branches *should* be prefixed like so:
-```
-release/{MAJOR}.{MINOR}
+There's a convenience script to create release branches from current `viable/strict` (from root `pytorch/pytorch`):
+
+```bash
+DRY_RUN=disabled scripts/release/cut-release-branch.sh
 ```
 
-An example of this would look like:
-```
-release/1.8
+This script should create 2 branches:
+* `release/{MAJOR}.{MINOR}`
+* `orig/release/{MAJOR}.{MINOR}`
+
+### `pytorch/builder` / PyTorch domain libraries
+
+Convenience script can also be used domains as well as `pytorch/builder`
+
+> NOTE: RELEASE_VERSION only needs to be specified if version.txt is not available in root directory
+
+```bash
+DRY_RUN=disabled GIT_BRANCH_TO_CUT_FROM=main RELEASE_VERSION=1.11 scripts/release/cut-release-branch.sh
 ```
 
-Please make sure to create branch that pins divergent point of release branch from the main branch, i.e. `orig/release/{MAJOR}.{MINOR}`
 ### Making release branch specific changes
 
 These are examples of changes that should be made to release branches so that CI / tooling can function normally on
 them:
 
-* Update target determinator to use release branch:
-  * Example: https://github.com/pytorch/pytorch/pull/40712
 * Update backwards compatibility tests to use RC binaries instead of nightlies
   * Example: https://github.com/pytorch/pytorch/pull/40706
 * A release branches should also be created in [`pytorch/xla`](https://github.com/pytorch/xla) and [`pytorch/builder`](https://github.com/pytorch/builder) repos and pinned in `pytorch/pytorch`
@@ -63,6 +74,7 @@ These are examples of changes that should be made to the *default* branch after
   * Example: https://github.com/pytorch/pytorch/pull/65435
 
 ### Getting CI signal on release branches:
+
 Create a PR from `release/{MAJOR}.{MINOR}` to `orig/release/{MAJOR}.{MINOR}` in order to start CI testing for cherry-picks into release branch.
 
 Example:

scripts/release/cut-release-branch.sh

@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+
+: '
+So you are looking to cut a release branch? Well you came
+to the right script.
+
+This script can be used to cut any branch on any repository
+
+For `pytorch/pytorch` usage would be like:
+> DRY_RUN=disabled cut-release-branch.sh
+
+For `pytorch/builder` or domains usage would be like:
+> DRY_RUN=disabled GIT_BRANCH_TO_CUT_FROM=main RELEASE_VERSION=1.11 cut-release-branch.sh
+'
+
+set -eou pipefail
+
+GIT_TOP_DIR=$(git rev-parse --show-toplevel)
+GIT_REMOTE=${GIT_REMOTE:-origin}
+GIT_BRANCH_TO_CUT_FROM=${GIT_BRANCH_TO_CUT_FROM:-viable/strict}
+
+# should output something like 1.11
+RELEASE_VERSION=${RELEASE_VERSION:-$(cut -d'.' -f1-2 "${GIT_TOP_DIR}/version.txt")}
+
+DRY_RUN_FLAG="--dry-run"
+if [[ ${DRY_RUN:-enabled} == "disabled" ]]; then
+    DRY_RUN_FLAG=""
+fi
+
+
+(
+    set -x
+    git fetch --all
+    git checkout "${GIT_REMOTE}/${GIT_BRANCH_TO_CUT_FROM}"
+)
+
+for branch in "release/${RELEASE_VERSION}" "orig/release/${RELEASE_VERSION}"; do
+    if git rev-parse --verify "${branch}" >/dev/null 2>/dev/null; then
+        echo "+ Branch ${branch} already exists, skipping..."
+        continue
+    else
+        (
+            set -x
+            git checkout "${GIT_REMOTE}/${GIT_BRANCH_TO_CUT_FROM}"
+            git checkout -b "${branch}"
+            git push "${GIT_REMOTE}" "${branch}"
+        )
+    fi
+done