Fixes var declaration shadowing in async functions#21215
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| function asyncBodyVisitor(node: Node): VisitResult<Node> { |
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Is there a canonical source we can reference in a comment here for the list-of-things-which-may-contain-or-whose-children-may-contain-hoisted-declarations? It seems nonobvious which elements of the statement and declaration list need to be explicitly visited here.
Also: Does LabeledStatement need to be handled? eg
async function fn4(x) {
lbl: {
var x = y;
}
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I've added isNodeWithPossibleVarDeclaration in 2ba29d8 as a way to verify this list.
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| function visitCatchClauseInAsyncBody(node: CatchClause) { | ||
| const catchClauseNames = createUnderscoreEscapedMap<true>(); | ||
| recordDeclarationName(node.variableDeclaration, catchClauseNames); |
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variableDeclaration may be undefined
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Actually, by the time we get to the es2017 transform a CatchClause must have a catch variable, otherwise it's not valid ES2017. Assigning the catch variable is handled in the esnext transform before the es2017 transform is run.
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I've added a test case in e655446 to verify this case.
| case SyntaxKind.LabeledStatement: | ||
| return visitEachChild(node, asyncBodyVisitor, context); | ||
| } | ||
| Debug.assert(!isNodeWithPossibleVarDeclaration(node), "Unhandled node."); |
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Why not make isNodeWithPossibleVarDeclaration into a type guard, start the function with it, then end with an assertNever to get the type checker to help out here?:
if(!isNodeWithPossibleVarDeclaration(node)) {
return visitor(node);
}
// ... switch block
Debug.assertNever(node, "Unhandled node.");
This fixes an issue where the downlevel emit for async functions to ES2015 can result in incorrect runtime semantics when the async function body contains a
vardeclaration that shadows a parameter name.Fixes #20461