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Assignment rest element pretends to get the contextual element type

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Jason Freeman
2015-04-10 16:03:54 -07:00
parent f84ebba852
commit 5bfbcdcd25
11 changed files with 92 additions and 7 deletions
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30
src/compiler/checker.ts
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@@ -6011,14 +6011,38 @@ module ts {
}
let hasSpreadElement = false;
let elementTypes: Type[] = [];
let inDestructuringPattern = isAssignmentTarget(node);
for (let e of elements) {
let type = checkExpression(e, contextualMapper);
elementTypes.push(type);
if (inDestructuringPattern && e.kind === SyntaxKind.SpreadElementExpression) {
// Given the following situation:
// var c: {};
// [...c] = ["", 0];
//
// c is represented in the tree as a spread element in an array literal.
// But c really functions as a rest element, and its purpose is to provide
// a contextual type for the right hand side of the assignment. Therefore,
// instead of calling checkExpression on "...c", which will give an error
// if c is not iterable/array-like, we need to act as if we are trying to
// get the contextual element type from it. So we do something similar to
// getContextualTypeForElementExpression, which will crucially not error
// if there is no index type / iterated type.
let restArrayType = checkExpression((<SpreadElementExpression>e).expression, contextualMapper);
let restElementType = getIndexTypeOfType(restArrayType, IndexKind.Number) ||
(languageVersion >= ScriptTarget.ES6 ? checkIteratedType(restArrayType, /*expressionForError*/ undefined) : undefined);
if (restElementType) {
elementTypes.push(restElementType);
}
}
else {
let type = checkExpression(e, contextualMapper);
elementTypes.push(type);
}
hasSpreadElement = hasSpreadElement || e.kind === SyntaxKind.SpreadElementExpression;
}
if (!hasSpreadElement) {
let contextualType = getContextualType(node);
if (contextualType && contextualTypeIsTupleLikeType(contextualType) || isAssignmentTarget(node)) {
if (contextualType && contextualTypeIsTupleLikeType(contextualType) || inDestructuringPattern) {
return createTupleType(elementTypes);
}
}