Babel parser typescript should throw when accessors do not agree in visibility

[JLHwung]

Bug Report

• I would like to work on a fix!

Current behavior

Parsed successfully.

• REPL

Input Code

class C99 {
	private get Baz():number { return 0; }
	public set Baz(n:number) {} // error - accessors do not agree in visibility
}

Expected behavior

Babel parser should throw when accessors do not agree in visibility

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)
REPL

Possible Solution

Additional context

Found this issue when reviewing #13089.

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[thorn0]

Should this really be considered a syntax error, not a semantic one?

[JLHwung]

I think if an error can be thrown in compile time (in contrast runtime is running the type checking), then any early error belongs to syntax error.

[fedeci]

Should we check for duplicate methods too?
REPL

[JLHwung]

Duplicate public methods are allowed in ECMAScript:

class C { foo() {}; foo(v) {} }

The TS error falls to diagnostic errors IMHO.

[fedeci]

I think we can check it here by looking for some other methods in classBody with kind === "get" || kind === "set" and the same name as the method to push.

babel/packages/babel-parser/src/plugins/typescript/index.js

Lines 2462 to 2488 in bdbd07d

	pushClassMethod(
	classBody: N.ClassBody,
	method: N.ClassMethod,
	isGenerator: boolean,
	isAsync: boolean,
	isConstructor: boolean,
	allowsDirectSuper: boolean,
	): void {
	const typeParameters = this.tsTryParseTypeParameters();
	if (typeParameters && isConstructor) {
	this.raise(typeParameters.start, TSErrors.ConstructorHasTypeParameters);
	}
	// $FlowIgnore
	if (method.declare && (method.kind === "get" || method.kind === "set")) {
	this.raise(method.start, TSErrors.DeclareAccessor, method.kind);
	}
	if (typeParameters) method.typeParameters = typeParameters;
	super.pushClassMethod(
	classBody,
	method,
	isGenerator,
	isAsync,
	isConstructor,
	allowsDirectSuper,
	);
	}

However it is almost useless if a user can specify multiple getters/setters with same name:

class C {
  public get foo() {}
  private get foo() {}
  public set foo(v) {}
}