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for (const x in #b) is allowed #58754
Description
🔎 Search Terms
Private identifier, for...in
🕗 Version & Regression Information
- This changed between versions 4.5.5 and 4.6.4
⏯ Playground Link
💻 Code
class A {
#b() {
for (const a in #b) {
}
}
}🙁 Actual behavior
No errors
🙂 Expected behavior
Error: Private identifiers are only allowed in class bodies and may only be used as part of a class member declaration, property access, or on the left-hand-side of an 'in' expression
Additional information about the issue
Noticed this while working on typescript-eslint/typescript-eslint#9232. There's a very suspicious condition in code: https://github.com/microsoft/TypeScript/blob/5a4134470128a062a8297f404dfb3321f8f55798/src/compiler/checker.ts#L33699
function checkGrammarPrivateIdentifierExpression(privId: PrivateIdentifier): boolean {
if (!getContainingClass(privId)) {
return grammarErrorOnNode(privId, Diagnostics.Private_identifiers_are_not_allowed_outside_class_bodies);
}
if (!isForInStatement(privId.parent)) {
if (!isExpressionNode(privId)) {
return grammarErrorOnNode(privId, Diagnostics.Private_identifiers_are_only_allowed_in_class_bodies_and_may_only_be_used_as_part_of_a_class_member_declaration_property_access_or_on_the_left_hand_side_of_an_in_expression);
}
const isInOperation = isBinaryExpression(privId.parent) && privId.parent.operatorToken.kind === SyntaxKind.InKeyword;
if (!getSymbolForPrivateIdentifierExpression(privId) && !isInOperation) {
return grammarErrorOnNode(privId, Diagnostics.Cannot_find_name_0, idText(privId));
}
}
return false;
}I don't know what isForInStatement is supposed to do there. I was unable to find the commit that introduced this—git blame took me to #44648 but that didn't have this condition.
Activity
bernard-wang commentedon Jun 7, 2024
Launched bug fix #58798 it seems that some of the logics were introduced in the bug fix #46824 .
Some of the thoughts here: first into logic getContainingClass(), after that, check whether it's in a for-in block and privId is the initializer part of the for-in, if so, this would be caught by the checkForInStatement().
Then into the isExpressionNode() logic, which would only allow privId be the left side of the In-expression, which the problem of right sight of for-in block would solved with a Error Diagnosis.
After these logic, we can make sure only privIds in In-expression come out and then we check its declaration.