fix: fixed getChild method of ParserRuleContext class

[AleiynikovPavel]

Problem

• I'm porting my code from the Java antlr4-runtime and TS antlr4ts libraries. In these libraries, the getChild method of class ParserRuleContext take a type that implements both TerminalNode and ParserRuleContext.
• antlr-4ng allows you to pass a type that implements only ParserRuleContext.
• This significantly complicates code porting because the library's API differs from its analogues.

  Сomparison of libraries

  TS antlr-4ng

  class ParserRuleContext have mthod getChild with declaration

  getChild<T extends ParseTree>(i: number, type: new (parent: ParserRuleContext | null, invokingStateNumber: number) => T): T | null;

  TS antlr4ts

  class ParserRuleContext have mthod getChild with declaration

  public getChild<T extends ParseTree>(i: number, ctxType: { new (...args: any[]): T; }): T;

  Java antlr4-runtime

  class ParserRuleContext have mthod getChild with declaration

  public <T extends ParseTree> T getChild(Class<? extends T> ctxType, int i);

  Conclusion

• I assume that the reference implementation for all libraries is the Java implementation. Because method getChild in Java take ParseTree interface, I think that your library should provide this too
• Due to the fact that in TS it is not possible to pass the interface type as a function argument, antlr4ts library method take the node type argument, casting it to the constructor type with argument - varargs of any (...args: any[])

• I assume that the antlr-4ng library does not use the any type. Because of this, the getChild method takes the ParserRuleContext class constructor as its second argument

  Comparison of node constructors in antlr-4ng

  Let's look at the constructors of all classes that implement the ParseTree interface

  ParserRuleContext

  Class ParserRuleContext extend RuleContext which implement ParseTree

  class ParserRuleContext extends RuleContext {
  
  constructor(parent: ParserRuleContext | null, invokingStateNumber: number);
  constructor(parent: ParserRuleContext | null, invokingStateNumber?: number);
  ...
  }

  TerminalNode

  Class TerminalNode implements ParseTree

  class TerminalNode implements ParseTree {
  
  constructor(symbol: Token);
  ...
  }

  ErrorNode

  Class ErrorNode extends TerminalNode and inherits its constructor

  class ErrorNode extends TerminalNode {
  ...
  }

  Conclusion

• From the comparison it is clear that of all the classes that implement ParseTree interface, the getChild method does not accept only TerminalNode and ErrorNode classes
• Сlasses TerminalNode and ErrorNode have the same constructor: constructor(symbol: Token);

Proposed changes

• From the above it follows that it is necessary to add support for an argument with the constructor type new (symbol: Token) => T to the getChild method of ParserRuleContext class.

[mike-lischke]

Good analysis, thanks! Your patch adds another overload signature, but looking at antlr4ts we can make this even simpler, by changing the existing context type signature to type: new (...args: unknown[]). This type only has one task (and hence the parameters are not relevant): it is used to check if a child is of this type.

And given that both overloads of getChildhave an index as first parameter, this entire signature can be reduced to:

    public override getChild<T extends ParseTree>(i: number, type?: new (...args: unknown[]) => T): T | null {
        ...
    }

What do you think?

[AleiynikovPavel]

I think type: new (...args: unknown[]) is a very good proposal. Especially if we assume that in the future new classes may appear that implement the ParseTree interface. Already added a new commit.