Add a GitHub Actions workflow for preparing a libcnb.rs release

.github/workflows/prepare-release.yml

@@ -0,0 +1,99 @@
+name: Prepare release
+
+on:
+  workflow_dispatch:
+    inputs:
+      bump:
+        description: "Which component of the version to increment"
+        required: true
+        default: "patch"
+        type: choice
+        options:
+          - major
+          - minor
+          - patch
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  prepare-release:
+    name: Prepare Release
+    runs-on: pub-hk-ubuntu-22.04-small
+    steps:
+      - name: Get token for GH application (Linguist)
+        uses: heroku/use-app-token-action@main
+        id: generate-token
+        with:
+          app_id: ${{ vars.LINGUIST_GH_APP_ID }}
+          private_key: ${{ secrets.LINGUIST_GH_PRIVATE_KEY }}
+
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          # We always want the version bump/changelog and resultant PR to target main, not the branch of the workflow_dispatch.
+          ref: main
+          # Using the GH application token here will configure the local git config for this repo with credentials
+          # that can be used to make signed commits that are attributed to the GH application user
+          token: ${{ steps.generate-token.outputs.app_token }}
+
+      - name: Update Rust toolchain
+        run: rustup update
+
+      - name: Rust Cache
+        uses: Swatinem/[email protected]
+
+      - name: Install cargo-edit
+        run: cargo install cargo-edit
+
+      - name: Record old crate version
+        id: old-version
+        run: echo "version=$(yq '.workspace.package.version' Cargo.toml)" >> "${GITHUB_OUTPUT}"
+
+      - name: Bump crate versions
+        # We use `--package libcnb` here to prevent the example and test buildpack crates from
+        # having their versions bumped too. Since the libcnb package's version is set via the
+        # root Cargo.toml's `workspace.package.version` field, all other publishable crates will
+        # still have their versions bumped, even though they are not explicitly listed here.
+        run: cargo set-version --package libcnb --bump '${{ inputs.bump }}'
+
+      - name: Record new crate version
+        id: new-version
+        run: echo "version=$(yq '.workspace.package.version' Cargo.toml)" >> "${GITHUB_OUTPUT}"
+
+      - name: Update changelog
+        run: |
+          OLD_VERSION='${{ steps.old-version.outputs.version }}'
+          NEW_VERSION='${{ steps.new-version.outputs.version }}'
+          DATE_TODAY="$(date --utc --iso-8601)"
+          UNRELEASED_URL="https://github.com/${{ github.repository }}/compare/v${NEW_VERSION}...HEAD"
+          NEW_VERSION_URL="https://github.com/${{ github.repository }}/compare/v${OLD_VERSION}...v${NEW_VERSION}"
+
+          sed --in-place --regexp-extended \
+            --expression "s~(^## \[Unreleased\])$~\1\n\n\n## [${NEW_VERSION}] - ${DATE_TODAY}~" \
+            --expression "s~(^\[unreleased\]:) .*$~\1 ${UNRELEASED_URL}\n[${NEW_VERSION}]: ${NEW_VERSION_URL}~" \
+            CHANGELOG.md
+
+      - name: Upgrade in-range dependency versions
+        run: cargo upgrade
+
+      - name: Create pull request
+        id: pr
+        uses: peter-evans/[email protected]
+        with:
+          token: ${{ steps.generate-token.outputs.app_token }}
+          title: Prepare release v${{ steps.new-version.outputs.version }}
+          body: |
+            Changes:
+            https://github.com/${{ github.repository }}/compare/v${{ steps.old-version.outputs.version }}...main
+          commit-message: Prepare release v${{ steps.new-version.outputs.version }}
+          branch: prepare-release
+          delete-branch: true
+          committer: ${{ vars.LINGUIST_GH_APP_USERNAME }} <${{ vars.LINGUIST_GH_APP_EMAIL }}>
+          author: ${{ vars.LINGUIST_GH_APP_USERNAME }} <${{ vars.LINGUIST_GH_APP_EMAIL }}>
+
+      - name: Configure pull request
+        if: steps.pr.outputs.pull-request-operation == 'created'
+        run: gh pr merge --auto --squash "${{ steps.pr.outputs.pull-request-number }}"
+        env:
+          GH_TOKEN: ${{ steps.generate-token.outputs.app_token }}

RELEASING.md

@@ -5,21 +5,11 @@ easier to gauge cross-crate compatibility.
 
 ## Prepare Release
 
-1. Create a new branch for the upcoming release
-2. Update [Cargo.toml](./Cargo.toml) in the root of the repository:
-   1. In the `workspace.package` table, update `version` to the new version
-   2. In the `workspace.dependencies` table, update the `version` of each of the repository-local dependencies to the new version
-3. Update [CHANGELOG.md](./CHANGELOG.md)
-   1. Move all content under `## [Unreleased]` to a new section that follows this pattern: `## [VERSION] - YYYY-MM-DD`
-   2. If appropriate, add a high-level summary of changes at the beginning of the new section
-   3. Update the version compare links at the bottom of the file to both add the new version, and update the "unreleased" link's "from" version.
-4. Install the latest version of [cargo-edit](https://github.com/killercup/cargo-edit): `cargo install cargo-edit`
-5. Bump in-range dependency versions using: `cargo upgrade`
-6. Commit the changes, push them and open a PR targeting `main`
+1. Trigger the [Prepare release](https://github.com/heroku/libcnb.rs/actions/workflows/prepare-release.yml) GitHub Actions workflow with a suitable `{patch,minor,major}` version bump.
 
 ## Release
 
-1. After peer-review, merge the release preparation PR
+1. Once the release preparation PR has been opened, review it (including ensuring the changelog is accurate) and then merge.
 2. On your local machine, run `git switch main && git pull` to ensure you're on the `main` branch with the latest changes
 3. Create a (lightweight) Git tag for the release and push it: (i.e. for version `1.1.38`: `git tag v1.1.38 && git push origin v1.1.38`) 
 4. Use `cargo` to release all crates, making sure to release dependencies of other crates first: