feat: refine changelog creation for releases (#51) (#52)

This change refines the way changelogs are calculated. The resulting
behavior is such that a release includes the commits that were made
on main since the previous release was minted and any commits made
on the specific release branch (such as targeted fixes or backports).
Prerelease is a running log of changes made to main since the most
recent release was minted.

.github/workflows/compile-changelog.rb

@@ -0,0 +1,77 @@
+
+# This script identifies the commits that have been made to the current
+# branch since the release before this branch. It formats them according
+# to a format specifier.
+#
+# Usage:
+#   compile-changelog outfile
+#
+#   outfile: the file location to write the changelog to
+
+module Git
+  def self.one_line_format(repository_url)
+    "[<code>%h</code>](#{repository_url}/commit/%h) %s (%an)"
+  end
+
+  def self.current_branch
+    `git rev-parse --abbrev-ref HEAD`.strip
+  end
+
+  def self.default_branch
+    `git rev-parse --abbrev-ref origin/HEAD`.strip
+  end
+
+  def self.default_branch_head
+    `git rev-parse origin/HEAD`.strip
+  end
+
+  def self.initial_commit
+    `git rev-list --max-parents=0 #{default_branch}`.strip
+  end
+
+  def self.release_branches
+    `git branch --list -r origin/release/*`.split("\n").map(&:strip)
+  end
+
+  def self.commit_date(commit)
+    `git show -s --format=%ct #{commit}`.strip
+  end
+
+  def self.merge_base_from(branch1, branch2)
+    `git merge-base #{branch1} #{branch2}`.strip
+  end
+
+  # Returns the commit where the given branch forked from the default git branch.
+  # If the given branch is the default git branch, the branch commit is the initial
+  # commit in the repo.
+  def self.merge_base(branch)
+    if branch == Git::default_branch_head
+      Git::initial_commit()
+    else
+      Git::merge_base_from(Git::default_branch, branch)
+    end
+  end
+
+  def self.formatted_commits_between(low, high, format)
+    `git log --pretty="format:#{format}" --no-merges #{low}..#{high}`
+  end
+end
+
+outfile = ARGV[0]
+repository_url = "https://github.com/#{ENV['GITHUB_REPOSITORY']}"
+commit_upper_bound = Git::current_branch
+commit_lower_bound = Git::release_branches
+                      .map     { |branch| Git::merge_base(branch) }
+                      .reject  { |commit| Git::commit_date(commit) >= Git::commit_date(commit_upper_bound) }
+                      .sort_by { |commit| Git::commit_date(commit) }
+                      .reverse
+                      .first
+
+changelog = Git::formatted_commits_between(
+  commit_lower_bound || Git::initial_commit,
+  commit_upper_bound,
+  Git::one_line_format(repository_url))
+
+File.open(outfile, 'a') do |file|
+  file.puts changelog
+end

.github/workflows/on-main-branch-change.yaml

@@ -0,0 +1,46 @@
+# Creates or updates a 'prerelease' release whenever main is
+# changed. Attaches a built PDF to that release.
+name: On Main Branch Change
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build_draft_pdf:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Git repository
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Set origin HEAD
+        run: git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
+
+      - name: Compile document
+        uses: xu-cheng/latex-action@v2
+        with:
+          root_file: ifc.tex
+          working_directory: ltx
+
+      - name: Compile changelog
+        run: |
+          echo 'CHANGELOG<<EOF' >> $GITHUB_ENV
+          ruby ./.github/workflows/compile-changelog.rb $GITHUB_ENV
+          echo 'EOF' >> $GITHUB_ENV
+
+      - name: Create prerelease
+        uses: ncipollo/release-action@v1
+        with:
+          token: "${{ secrets.GITHUB_TOKEN }}"
+          allowUpdates: true
+          name: Prerelease
+          prerelease: true
+          tag: prerelease
+          body: |
+            This release is a prerelease. The contents of this release are likely to change.
+            # Changelog
+            ${{ env.CHANGELOG }}
+          artifacts: |
+            ltx/ifc.pdf

.github/workflows/on-release-branch-change.yml

@@ -0,0 +1,50 @@
+# Creates or updates a release's generated PDF when a change occurs
+# to a release branch
+name: On Release Branch Change
+on:
+  push:
+    branches:
+      - "release/*"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Git repository
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Set origin HEAD
+        run: git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
+
+      - name: Extract branch name
+        shell: bash
+        run: echo "RELEASE_NAME=$(echo ${GITHUB_REF#refs/heads/release/})" >> $GITHUB_ENV
+
+      - name: Compile document
+        uses: xu-cheng/latex-action@v2
+        with:
+          root_file: ifc.tex
+          working_directory: ltx
+
+      - name: Compile changelog
+        run: |
+          echo 'CHANGELOG<<EOF' >> $GITHUB_ENV
+          ruby ./.github/workflows/compile-changelog.rb $GITHUB_ENV
+          echo 'EOF' >> $GITHUB_ENV
+
+      - name: Update release
+        uses: ncipollo/release-action@v1
+        with:
+          token: "${{ secrets.GITHUB_TOKEN }}"
+          allowUpdates: true
+          name: ${{ env.RELEASE_NAME }}
+          prerelease: false
+          tag: ${{ env.RELEASE_NAME }}
+          body: |
+            # Changelog
+            ${{ env.CHANGELOG }}
+          artifacts: |
+            ltx/ifc.pdf
+

.github/workflows/on-release-created.yml

@@ -0,0 +1,37 @@
+# Creates a release branch whenever a release is created.
+
+name: On Release Created
+on:
+  release:
+    types:
+      - published
+
+jobs:
+  create_branch:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: peterjgrainger/action-create-branch@v2.0.1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          branch: 'release/${{ github.event.release.tag_name }}'
+
+  build_latex:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Git repository
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Compile document
+        uses: xu-cheng/latex-action@v2
+        with:
+          root_file: ifc.tex
+          working_directory: ltx
+
+      - name: Add PDF to Release
+        uses: softprops/action-gh-release@v0.1.13
+        if: startsWith(github.ref, 'refs/tags/')
+        with:
+          files: ltx/ifc.pdf