message: Add `requires` api
diff: @@ -17,6 +17,9 @@ pub trait Analyzer : Any + Debug {
  /// Return the kind of this `Analyzer`.
  fn kind(&self) -> AnalyzerKind;
  +
  + /// Return a list of `Analyzer`s to run before this one.
  + fn requires(&self) -> Vec<AnalyzerKind>;
  }
  /// An `Analyzer` that takes a function.
  