Create GitHub Actions release automation

Signed-off-by: Nathaniel Graff <[email protected]>

.github/workflows/release.yml

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+on:
+  push:
+    # Require one of the following patterns to match the tag
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+.[0-9]+' # ex. v20.00.00.00
+      - 'v[0-9]+.[0-9]+.RC.[0-9]+'     # ex. v20.00.RC.00
+
+name: Create Release
+
+env:
+  PROJECT_NAME: freedom-devicetree-tools
+  # Release is a prerelease if the tag contains rc
+  PRERELEASE: ${{ contains(github.ref, 'RC') }}
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: 'Checkout'
+        uses: actions/checkout@v2
+
+      # In order to generate release notes, we need a deep clone of the
+      # repository so that we can find the most recent tag and generate
+      # statistics based on it.
+      - name: 'Fetch History'
+        run: git fetch --prune --unshallow
+
+      - name: 'Create Release Notes'
+        id: create-release-notes
+        run: |
+          tag=$(echo ${{ github.ref }} | cut -d '/' -f 3)
+          release_notes=$(./scripts/create-release-notes.sh ${{ env.PROJECT_NAME }} ${tag})
+          # The string passed to Actions must urlencode newlines.
+          release_notes="${release_notes//$'\n'/'%0A'}"
+          # Use a magic "workflow command" to set the output for the step.
+          echo "::set-output name=release-notes::${release_notes}"
+
+      - name: 'Create Release'
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          tag_name: ${{ github.ref }}
+          release_name: ${{ env.PROJECT_NAME }} ${{ github.ref }}
+          body: ${{ steps.create-release-notes.outputs.release-notes }}
+          draft: false
+          prerelease: ${{ env.PRERELEASE }}

scripts/create-release-notes.sh

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+#!/bin/bash
+# Copyright (c) 2020 SiFive Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+set -euo pipefail
+
+if [ "$#" -lt 2 ] ; then
+  >&2 echo "$0: please provide project name and release tag"
+  exit 1
+fi
+
+project=$1; shift 1;
+current_release=$1; shift 1;
+
+# Get the most recent previous tag with git-describe. If this is
+# the first tag in the repository, then this will return a commit
+# hash (because of the --always flag).
+last_release=$(git describe --tags --always HEAD~)
+
+echo "# Release notes for ${project} ${current_release}"
+echo "## Statistics since ${last_release}"
+echo "- $(git rev-list --count ${last_release}..HEAD) commits"
+echo "-$(git diff --shortstat ${last_release} HEAD)"
+echo ""
+echo "## Authors"
+git shortlog -s -n --no-merges ${last_release}..HEAD | cut -f 2
+echo ""
+echo "## Merge history"
+git log --merges --pretty=format:"%h %b" ${last_release}..HEAD