Clarify the use of 'using' as a variable reference expression in for loop conditions

[kaleidawave]

There are currently two tests which show the fallback behaviour of using as variable identifiers

test262/test/language/statements/using/syntax/using-invalid-arraybindingpattern-does-not-break-element-access.js

Lines 11 to 15 in dc0a351

	var using = [], x = 0;
	{
	using[x] = null;
	}

test262/test/language/statements/await-using/syntax/await-using-invalid-arraybindingpattern-does-not-break-element-access.js

Lines 15 to 17 in dc0a351

	asyncTest(async function () {
	await using[x];
	});

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I was looking whether there were similar tests for the for (using x of|in ...) feature but I could not find anything.

Running two on Safari (so webkit). The following parses as variable using

for (using = 0; using < 2; using += 1) console.log(0, using)

This next case parses if and only it is inside a async function

for (await using; using < 4; using += 1) console.log(1, using)

I haven't looked at the specification. It might be consulting that before adding tests for these. I can add a PR once details are known.

[ptomato]

cc @rbuckton

[rbuckton]

using is a contextual keyword. In most contexts, it remains a valid identifier. Only when it is used as a variable declaration keyword (like const) is it treated as a using declaration. The same is true for await using. In both of the for loop examples you've shown, using would be interpreted as a keyword. Only if you write for (using x ... would it be treated as a declaration.