The Observatorium API has a special-purpose LogQL parser for applying matcher patchers on the label selectors (see pkg/logql/v2). The reason having a custom implementation is lack of license compatibility (observatorium-api is Apache 2.0 and Loki AGPLv3+). From time to time Loki receives updates on the LogQL packaged that require us to add support in our implementation. To catch what changes between minor version use a similar command as:

git log --oneline upstream/release-2.6.x...upstream/release-2.7.x -- pkg/logql/syntax/expr.y