Validating Renovate configuration changes before merging

If you're developing custom rules within Renovate, in particular as part of shareable config presets but even if they're just within your repo, it's handy to be able to test it first.

This is something I've done several times and have put together a little boilerplate for, so thought I'd blogument it.

We can create a file, config.js and add the following configuration to it. Note that this must be called config.js for Renovate to pick it up.

module.exports = {
  // --------------------------------------------------------------------------------
  // required configuration, which makes sure that we don't require Renovate configuration, and even if it's there, we ignore it
  "onboarding": false,
  "requireConfig": "ignored",

  // --------------------------------------------------------------------------------
  // optional configuration

  // optional but recommended to keep if you don't want to have PRs/issues raised. Alternatively, set it to `full` to see what Renovate would compute as expected updates
  "dryRun": "extract",

  // --------------------------------------------------------------------------------
  // finally, the configuration we're looking to validate

  // make sure that we reduce the work that this test run is going to perform - this isn't meant to be in your production configuration!
  "enabledManagers": [
    "regex"
  ],

  // the actual rules
  "regexManagers": [
    {
      "fileMatch": [
        "^tools/dev/loki-boltdb-storage-s3/dev.dockerfile$"
      ],
      "matchStrings": [
        "go install (?<depName>[^@]+?)@(?<currentValue>v[0-9.-a-zA-Z]+)"
      ],
      "datasourceTemplate": "go"
    }
  ]
}

Notice that we're writing our configuration as if it's JSON - this is intentional to make it easier to copy-paste between the config.js and our subsequent JSON configuration.

Then we can run:

# I'd recommend using `LOG_LEVEL` to get more info about exactly what Renovate has parsed out of your rules
env LOG_LEVEL=debug renovate --token $GITHUB_TOKEN grafana/loki

This will then give us:

DEBUG: Applying enabledManagers filtering (repository=grafana/loki)
DEBUG: Using file match: ^tools/dev/loki-boltdb-storage-s3/dev.dockerfile$ for manager regex (repository=grafana/loki)
DEBUG: Matched 1 file(s) for manager regex: tools/dev/loki-boltdb-storage-s3/dev.dockerfile (repository=grafana/loki)
DEBUG: manager extract durations (ms) (repository=grafana/loki)
       "managers": {"regex": 2}
DEBUG: Found regex package files (repository=grafana/loki)
DEBUG: Found 1 package file(s) (repository=grafana/loki)
 INFO: Dependency extraction complete (repository=grafana/loki, baseBranch=main)
       "stats": {
         "managers": {"regex": {"fileCount": 1, "depCount": 1}},
         "total": {"fileCount": 1, "depCount": 1}
       }
 INFO: Extracted dependencies (repository=grafana/loki)
       "packageFiles": {
         "regex": [
           {
             "deps": [
               {
                 "depName": "github.com/go-delve/delve/cmd/dlv",
                 "currentValue": "v1.20.2",
                 "datasource": "go",
                 "replaceString": "go install github.com/go-delve/delve/cmd/dlv@v1.20.2"
               }
             ],
             "matchStrings": [
               "go install (?<depName>[^@]+?)@(?<currentValue>v[0-9.-a-zA-Z]+)"
             ],
             "datasourceTemplate": "go",
             "packageFile": "tools/dev/loki-boltdb-storage-s3/dev.dockerfile"
           }
         ]
       }

Which as we can see, has successfully picked up the right dependency and version.

(Aside - this exact example doesn't quite work)