Feature: Mutant filters

[nicojs]

Is your feature request related to a problem? Please describe.

We want to add a mutator that removes statements or expressions. I.e. #3916

-resource.dispose();
+ // 👽

However, this would result in many additional mutants without real value since another mutant already covered the statement. For example, we wouldn't want to remove this statement:

- const result = foo + bar;
+ const result = foo - bar; // 👽

Describe the solution you'd like

We would like to be able to filter mutants using a MutantFilter, like is implemented in Stryker.NET: https://github.com/stryker-mutator/stryker-net/blob/master/src/Stryker.Core/Stryker.Core/MutantFilters/IgnoreBlockMutantFilter.cs#L10

Note: we shouldn't mark filtered-out mutants as 'ignored'; they should not exist in your report.

A valid approach might be to add an optional filter method on the mutator API, that, when implemented, indicated whether or not the mutant is valid.

export interface NodeMutator {
  mutate(path: NodePath): Iterable<types.Node>;
+ filter?(mutableInScope: Mutable[]): boolean;
  readonly name: string;
}

Describe alternatives you've considered

Keep like it is now, with a lot of noise when implementing the statement mutator.

Additional context

0