const [y, y] = [] throws a TypeError, instead of SyntaxError

[p-bakker]

Followup of #386

[tuchida]

Perhaps this is the same problem.

const y = undefined;
const y = undefined; // SyntaxError, but TypeError in Rhino

It should not be possible to achieve this without implementing TDZ.

[p-bakker]

Is this really related to TDZ? IMHO this is just about redeclaration of a const, whereas TDZ is about accessing a const before it is declared, with let/const not being hoisted to the top of a function like vars, but only being defined as the point in the code where they are declared, so any code accessing them before they are declared is what TDZ is about (AFAIK)

[tuchida]

Sorry, this may not be directly related.
However, if the redeclaration check is to be done in the parse phase instead of the execution phase, I think TDZ will have to be implemented at the same time.

[p-bakker]

To my knowledge TDZ issues throw a ReferenceError and I think those are runtime errors, not parse-time errors.

And redeclaration of const/let throws a SyntaxError, which is a parse-time error I think

[tuchida]

ref. #1519, #1520
After applying these, I got the following error.
I made a merging mistake. It will still be a TypeError as before.

$ ./gradlew run -q --console=plain --args="-version 200"
Rhino 1.7.16-SNAPSHOT
js> const [y, y] = []
js: line 2: TypeError: redeclaration of const y.
js: 
js: ^

[tuchida]

Errors whose message starts with TypeError: are TypeError.

rhino/rhino/src/main/java/org/mozilla/javascript/DefaultErrorReporter.java

Lines 39 to 55 in 7feaad0

	@Override
	public void error(String message, String sourceURI, int line, String lineText, int lineOffset) {
	if (forEval) {
	// Assume error message strings that start with "TypeError: "
	// should become TypeError exceptions. A bit of a hack, but we
	// don't want to change the ErrorReporter interface.
	String error = "SyntaxError";
	final String TYPE_ERROR_NAME = "TypeError";
	final String DELIMETER = ": ";
	final String prefix = TYPE_ERROR_NAME + DELIMETER;
	if (message.startsWith(prefix)) {
	error = TYPE_ERROR_NAME;
	message = message.substring(prefix.length());
	}
	throw ScriptRuntime.constructError(
	error, message, sourceURI, line, lineText, lineOffset);
	}

Perhaps all of these are fine with SyntaxError.

rhino/rhino/src/main/resources/org/mozilla/javascript/resources/Messages.properties

Lines 268 to 281 in 7feaad0

	msg.var.redecl =\
	TypeError: redeclaration of var {0}.
	msg.const.redecl =\
	TypeError: redeclaration of const {0}.
	msg.let.redecl =\
	TypeError: redeclaration of variable {0}.
	msg.parm.redecl =\
	TypeError: redeclaration of formal parameter {0}.
	msg.fn.redecl =\
	TypeError: redeclaration of function {0}.

rhino/rhino/src/main/resources/org/mozilla/javascript/resources/Messages.properties

Lines 474 to 478 in 7feaad0

	msg.generator.returns =\
	TypeError: generator function {0} returns a value
	msg.anon.generator.returns =\
	TypeError: anonymous generator function returns a value

// old generator
function g() { return 0; yield 1; }
// js: "<stdin>", line 2: TypeError: generator function g returns a value
// js: function g() { return 0; yield 1; }
// js: ................................^
// js: "<stdin>", line 2: Compilation produced 1 syntax errors.

// latest generator
function *g() { return 0; yield 1; }  // no error

However, TypeError is correct if the constant is overwritten at runtime. A different message would be needed in this case.

rhino/rhino/src/main/java/org/mozilla/javascript/ScriptableObject.java

Lines 2192 to 2200 in 7feaad0

	public static void redefineProperty(Scriptable obj, String name, boolean isConst) {
	Scriptable base = getBase(obj, name);
	if (base == null) return;
	if (base instanceof ConstProperties) {
	ConstProperties cp = (ConstProperties) base;
	if (cp.isConst(name)) throw ScriptRuntime.typeErrorById("msg.const.redecl", name);
	}
	if (isConst) throw ScriptRuntime.typeErrorById("msg.var.redecl", name);

function NaN() {} // TypeError

[tuchida]

Fixed by #1530.