Add release-please to automate releases

Set up release-please with java release type and always-bump-patch
versioning. This replaces the manual release process: release-please
maintains a release PR, and merging it creates a tag that triggers
the existing Maven Central deploy workflow.

Remove bump_snapshot.py and set-version.sh scripts as release-please
handles SNAPSHOT version bumps automatically.
Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

.github/workflows/release-please.yml

@@ -0,0 +1,20 @@
+---
+name: Release Please
+
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  release-please:
+    if: ${{ github.repository == 'prometheus/client_java' }}
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: googleapis/release-please-action@16a9c90856f42705d54a6fda1823352bdc62cf38 # v4.4.0
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}

.mise/tasks/bump_snapshot.py

@@ -0,0 +1,13 @@
+{
+  "$schema": "https://raw.githubusercontent.com/googleapis/release-please/main/schemas/config.json",
+  "packages": {
+    ".": {
+      "release-type": "java",
+      "versioning": "always-bump-patch",
+      "extra-files": [
+        "prometheus-metrics-parent/pom.xml",
+        "integration-tests/it-spring-boot-smoke-test/pom.xml"
+      ]
+    }
+  }
+}

.mise/tasks/set-version.sh

@@ -0,0 +1,3 @@
+{
+  ".": "1.5.0"
+}

.release-please-config.json

@@ -56,6 +56,15 @@ or simply
 mise run compile
 ```
 
+## Version Numbers in Examples
+
+Example `pom.xml` files (under `examples/`) should reference the latest
+**released** version, not a SNAPSHOT. After each release, Renovate
+updates these versions automatically.
+
+Only use a SNAPSHOT version in an example when it demonstrates a new
+feature that has not been released yet.
+
 ## Updating the Protobuf Java Classes
 
 The generated protobuf `Metrics.java` lives in a versioned package

.release-please-manifest.json

@@ -1,44 +1,58 @@
 # Releasing Instructions for Prometheus Java Client
 
-## Before the Release
+Releases are automated via
+[release-please](https://github.com/googleapis/release-please).
 
-If there have been significant changes since the last release, update the
-benchmarks before creating a new release:
+## How It Works
 
-```shell
-mise run update-benchmarks
-```
+1. Commits to `main` using
+   [Conventional Commits](https://www.conventionalcommits.org/) are
+   tracked by release-please.
+2. Release-please maintains a release PR that accumulates changes and
+   updates the changelog.
+3. When the release PR is merged, release-please creates a GitHub
+   release and a `vX.Y.Z` tag.
+4. The tag triggers the existing `release.yml` workflow, which deploys
+   to Maven Central.
+5. After tagging, release-please opens a follow-up PR to bump the
+   SNAPSHOT version in all `pom.xml` files.
 
-## Create a Release
+## Patch Release (default)
 
-1. Go to <https://github.com/prometheus/client_java/releases/new>
-2. Click on "Choose a tag", enter the tag name (e.g. `v0.1.0`), and click "Create a new tag".
-3. Click on "Generate release notes" to auto-generate the release notes based on the commits since
-   the last release.
-4. Click on "Publish release".
+Simply merge the release PR — release-please bumps the patch version
+by default (e.g. `1.5.0` -> `1.5.1`).
 
-## Major or minor release
+## Minor or Major Release
 
-After the release is created, bump the snapshot version in all
-`pom.xml` files:
+Add a `release-as: X.Y.0` footer to any commit on `main`:
 
-```shell
-# Auto-increment the minor version (e.g. 1.5.0-SNAPSHOT -> 1.6.0-SNAPSHOT)
-mise run bump-snapshot
+```text
+feat: add new feature
+
+release-as: 1.6.0
+```
 
-# Or specify an explicit version (e.g. for a major bump)
-mise run bump-snapshot 2.0.0-SNAPSHOT
+Alternatively, edit the release PR title to
+`chore(main): release 1.6.0`.
+
+## Before the Release
+
+If there have been significant changes since the last release, update
+the benchmarks before merging the release PR:
+
+```shell
+mise run update-benchmarks
 ```
 
-## If the GPG key expired
+## If the GPG Key Expired
 
 1. Generate a new key:
    <https://central.sonatype.org/publish/requirements/gpg/#generating-a-key-pair>
-2. Distribute the
-   key: <https://central.sonatype.org/publish/requirements/gpg/#distributing-your-public-key>
-3. use `gpg --armor --export-secret-keys YOUR_ID` to
-   export ([docs](https://github.com/actions/setup-java/blob/main/docs/advanced-usage.md#gpg))
-4. Update the
-   passphrase: <https://github.com/prometheus/client_java/settings/secrets/actions/GPG_SIGNING_PASSPHRASE> <!-- editorconfig-checker-disable-line -->
-5. Update the GPG
-   key: <https://github.com/prometheus/client_java/settings/secrets/actions/GPG_SIGNING_KEY>
+2. Distribute the key:
+   <https://central.sonatype.org/publish/requirements/gpg/#distributing-your-public-key>
+3. Use `gpg --armor --export-secret-keys YOUR_ID` to export
+   ([docs](https://github.com/actions/setup-java/blob/main/docs/advanced-usage.md#gpg))
+4. Update the passphrase:
+   <https://github.com/prometheus/client_java/settings/secrets/actions/GPG_SIGNING_PASSPHRASE>
+5. Update the GPG key:
+   <https://github.com/prometheus/client_java/settings/secrets/actions/GPG_SIGNING_KEY>