Add automated release workflow (#2586)

Some of the upstream PRs are getting backported to the llvm_release_* branches, but those changes are never released. That prevents them from distributing as precompiled packages in various distributions like conda-forge and others. This PR targets this issue by creating automated workflow that is triggered once a month and generates automated releases for each such branch if there were changes since last release.

This PR
Adds workflow to generate releases every month from llvm_release_* branches in the format %llvm_major%.%llvm_minor%.%latest patch version +1%. For example:
v18.1.1
v17.0.2
v17.0.1
v14.0.1
etc

Release description matches as close as possible to current releases. The only difference is that llvm versions is represented by two numbers, instead of three, because it is impossible to recover exact version. You can check out example of generated versions here (there are few releases from the original proposal): https://github.com/ZzEeKkAa/SPIRV-LLVM-Translator/releases
Workflow is set to be triggered once a month. It is also possible to trigger it manually from github actions UI.

Merge process
Merge the PR to main
Trigger workflow manually

Note
There is no need to backport changes to all branches, since workflow dispatch on schedule basis can be performed only from main branch.

Fixes: #1898
Fixes: #1508

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@63e89a9a268e5c2

Author: ZzEeKkAa

llvm-spirv/.github/workflows/patch-release.yaml

@@ -0,0 +1,88 @@
+name: Automated release
+
+on:
+  workflow_dispatch:
+  schedule:
+    # First day of every month
+    - cron: '0 0 1 * *'
+
+jobs:
+  setup:
+    runs-on: ubuntu-latest
+    outputs:
+      latest_branch: ${{steps.latest_branch.outputs.latest_branch}}
+      branches_json: ${{steps.release_branches.outputs.branches_json}}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+            fetch-depth: 0
+      - name: Get latest llvm_release branch
+        id: latest_branch
+        run: |
+          git branch -r \
+          | grep 'llvm_release_' \
+          | sed -E 's/.*\/llvm_release_([0-9]+)/\1/' \
+          | sort -n -r \
+          | head -1 \
+          | xargs printf "latest_branch=llvm_release_%s" \
+          >> $GITHUB_OUTPUT
+      - name: Get branch list
+        id: release_branches
+        run: |
+          git branch -r \
+          | grep "origin/llvm_release_" \
+          | sed -E 's/\ *origin\/([^\ ]*)/\"\1\"/' \
+          | paste -sd',' \
+          | xargs -0 -d"\n" printf 'branches_json={"branch":[%s]}' \
+          >> $GITHUB_OUTPUT
+  release:
+    runs-on: ubuntu-latest
+    needs: setup
+    strategy:
+      matrix: ${{fromJson(needs.setup.outputs.branches_json)}}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+            ref: ${{ matrix.branch }}
+            fetch-depth: 0
+      - name: Get commits info
+        id: versions
+        run: |
+            export LATEST_VERSION=\
+            "$(git describe --tags --abbrev=0 --match 'v*')"
+            export LLVM_VERSION=$(echo $LATEST_VERSION \
+            | sed -E 's/(v[0-9]+\.[0-9]+)\.([0-9]+).*/\1/')
+            export PATCH=$(echo $LATEST_VERSION \
+            | sed -E 's/(v[0-9]+\.[0-9]+)\.([0-9]+).*/\2/')
+
+            echo "llvm_version=$LLVM_VERSION" >> $GITHUB_OUTPUT
+            echo "patch=$PATCH" >> $GITHUB_OUTPUT
+            echo "latest_version=${LATEST_VERSION}" >> $GITHUB_OUTPUT
+            echo "release_version=${LLVM_VERSION}.$((${PATCH}+1))" \
+            >> $GITHUB_OUTPUT
+
+            git rev-list ${LATEST_VERSION}..HEAD --count \
+            | xargs printf "commits_since_last_release=%d\n" >> $GITHUB_OUTPUT
+            git rev-parse HEAD | xargs printf "last_commit=%s\n" >> $GITHUB_OUTPUT
+      - name: Release
+        uses: softprops/action-gh-release@v2
+        if: ${{ steps.versions.outputs.commits_since_last_release != 0 }}
+        with:
+            # Setting tag to have format:
+            # %latest llvm version%.%latest patch + 1%
+            tag_name: ${{ steps.versions.outputs.release_version }}
+            # We have to set this so tag is set on the branch we are releasing
+            target_commitish: ${{ steps.versions.outputs.last_commit }}
+            # We don't want to mark patch releases latest unless it is latest
+            # major version
+            make_latest: >-
+              ${{ needs.setup.outputs.latest_branch == matrix.branch }}
+            name: >
+              SPIR-V LLVM translator based on LLVM
+              ${{ steps.versions.outputs.llvm_version }}
+            body: "Full Changelog: ${{ github.server_url }}/\
+              ${{ github.repository }}/compare/\
+              ${{ steps.versions.outputs.latest_version }}...\
+              ${{ steps.versions.outputs.release_version }}"

llvm-spirv/README.md

@@ -256,3 +256,9 @@ LLVM/Clang release and there are no objections from the maintainer(s). There
 is no guarantee that older release branches are proactively kept up to date
 with main, but you can request specific commits on older release branches by
 creating a pull request or raising an issue on GitHub.
+
+## Releasing strategy
+
+As mentioned earlier there are branches `llvm_release_*` that get backported
+changes. Those changes if exists are released automatically by github CI on
+monthly basis in a format `<llvm_major>.<llvm_minor>.<latest patch +1>`.