Help adding support for more complex string literal types with infer

[trevordixon]

I'd love to support something like this:

type SnakeToCamelCase<S extends string> =
    S extends `${infer T}_${infer U}` ?
    `${T}${Capitalize<SnakeToCamelCase<U>>}` : S;

type C = SnakeToCamelCase<'some_thing'>;

Right now, C seems just to become string. Could you give me a pointer where to start to add support for this?

[trevordixon]

I used this to handle type-fest's DelimiterCase.

class DelimiterCaseParser implements SubNodeParser {
  public constructor(
    protected typeChecker: ts.TypeChecker,
    protected childNodeParser: NodeParser,
  ) { }

  public supportsNode(node: ts.Node): boolean {
    return ts.isTypeReferenceNode(node) && node.typeName.getText() === 'DelimiterCase';
  }

  public createType(node: ts.TypeReferenceNode, context: Context, reference?: ReferenceType): BaseType {
    const [propNode, delimNode] = node.typeArguments!;
    const propType = this.childNodeParser.createType(propNode, context) as LiteralType;
    const delimType = this.childNodeParser.createType(delimNode, context) as LiteralType;
    return new LiteralType(
      String(propType.getValue()).replace(/[A-Z]/g, letter =>
        `${delimType.getValue()}${letter.toLowerCase()}`
      ),
    );
  }
}