Configure Renovate to suggest AGP version bumps

[gabrielfeo]

Automate the discovery of new AGP versions. While there's an existing workflow for bumping the AGP versions in this project, it must be manually triggered specifying the new version. Renovate can fill this gap by suggesting updates whenever new versions come out.

Renovate

Renovate is a tool like Dependabot but much more flexible. It has built-in "managers" such as maven, gradle, and pip_requirements that look for certain patterns in certain files, then query "datasources" for newer versions. No built-in manager supports the custom versions.json file, but Renovate allows for creating a custom regex-based manager.

Renovate custom manager

A Renovate config file is added with a custom "regex" manager. This can instruct Renovate to parse any version on any file. The goal is to detect and update AGP versions annotated with a comment:

# renovate: AGP version
8.6.0

The "manager" config declares

• what files it should process
• what it should consider a version definition within those files
• what "datasource" it should query for newer versions
• what "versioning" (scheme) the versions adhere to
• the dependency name
• the Maven registry URL the dependency comes from

{
  // Matches AGP versions annotated with a "renovate: AGP version" comment
  customType: "regex",
  fileMatch: [
    "src/main/resources/versions\\.json5",
    "gradle\\.properties",
  ],
  matchStrings: [
    // For JSON: the first double-quoted string below the comment line, e.g. "1.0.0"
    "\/\/ renovate: AGP version\\s+?\"(?<currentValue>\\S+?)\"",
    // For properties: the value of the first property below the comment line, e.g. anyProperty=1.0.0
    "# renovate: AGP version\\s+?\\S+?=(?<currentValue>\\S+?)(?:\\s|$)",
  ],
  "datasourceTemplate": "maven",
  "versioningTemplate": "maven",
  "depNameTemplate": "com.android.tools.build:gradle",
  "registryUrlTemplate": "https://dl.google.com/dl/android/maven2/",
},

An example PR is available in a fork: gabrielfeo#10.

The last four elements are commonly set on each comment and captured with regex (example), but I opted to centralize them in the Renovate config to minimize duplication, simplify the comments and the regex that parses them.

Changes

• Annotate AGP versions in versions.json with a "renovate: AGP version" comment
  • Rename the file to versions.json5 to keep syntax highlighting support when adding comments
  • Change all JsonSlurpers to LAX mode, which is lenient about comments (Groovy has no support for JSON5)
• Add a Renovate config to bump versions in versions.json5 and gradle.properties too (for the build-time check described below)
• Change plugin tests to no longer require changes on every patch version. "expectedOutcomes" JSON files are now minor-specific and WorkaroundTest no longer specifies patch numbers. Updating these is something that the existing workflow takes care of, but can't be as easily done with Renovate. Thanks to @erichaagdev for this suggestion.
• Declare the latest AGP version in gradle.properties and fail the build if it's missing from versions.json5. The goal is to have Renovate create a "nudge" PR if a new major or minor comes out (versions.json5 has major/minor bumps disabled in order to keep older minor versions in the list of "supportedVersions"). The property isn't used for anything else. Thanks to @erichaagdev for this suggestion.

Pending work

• Find how to keep Renovate updating older versions, e.g. 8.6.0 to 8.6.1 despite 8.7.1 being out (worked out in commit gabrielfeo@f92e638)
• Revert the downgrade commits that were added for testing from the PR branch
• Find out if Renovate is enabled for all repos in the org (or ask for it to be enabled in this repo)