Packages not grouped with "update-lockfile" range strategy

[mbrodala]

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Describe the bug

Given the following renovate.json:

{
  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
  "extends": [
    "config:base"
  ],
  "rangeStrategy": "update-lockfile",
  "packageRules": [
    {
      "matchPackagePrefixes": [
        "phpstan/"
      ],
      "matchPackageNames": [
        "jangregor/phpstan-prophecy",
        "saschaegerer/phpstan-typo3",
        "rector/rector"
      ],
      "groupName": "PHPStan"
    }
  ]
}

And the following composer.json:

{
    "require-dev": {
        "jangregor/phpstan-prophecy": "^0.8.0",
        "phpstan/phpstan": "^0.12.30",
        "rector/rector": "^0.11.57",
        "saschaegerer/phpstan-typo3": "^0.13"
    }
}

As can be seen, there's a package rule to group all PHPStan packages and related 3rd party packages. Strangely the rector/rector package is not part of the PHPStan package group update:

Since rector/rector 0.12.x depends on phpstan/phpstan 1.x both update pull requests are broken.

See mbrodala/renovate-phpstan-package-group#1 for a live example.

What am I missing?

Relevant debug logs

Logs

DEBUG: Dependency rector/rector is part of group PHPStan
DEBUG: Using group branchName template
DEBUG: Dependency saschaegerer/phpstan-typo3 is part of group PHPStan
DEBUG: 4 flattened updates found: jangregor/phpstan-prophecy, phpstan/phpstan, rector/rector, saschaegerer/phpstan-typo3
DEBUG: Returning 2 branch(es)
DEBUG: Fetching changelog: https://github.com/sascha-egerer/phpstan-typo3 (0.13.3 -> 1.0.0)
DEBUG: Fetching changelog: https://github.com/phpstan/phpstan (0.12.99 -> 1.2.0)
DEBUG: Fetching changelog: https://github.com/Jan0707/phpstan-prophecy (0.8.1 -> 1.0.0)
DEBUG: Fetching changelog: https://github.com/rectorphp/rector (0.11.60 -> 0.12.4)

Have you created a minimal reproduction repository?

I have linked to a minimal reproduction repository in the bug description

[rarkins]

Groups are split between major and minor by default. If you really want them to be combined, you could try setting separateMajorMinor=false

[mbrodala]

That makes sense, and indeed adding "separateMajorMinor": false to the PHPStan package group made Renovate behave like expected:

Maybe this fact should be mentioned in the docs for separateMajorMinor.