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Disallow conditional type following 'extends'

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This commit is contained in:
Anders Hejlsberg
2018-01-19 14:44:48 -08:00
parent c360c24b9b
commit 0e73240ea4
1 changed files with 14 additions and 17 deletions
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src/compiler/parser.ts
+14 -17
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@@ -2882,21 +2882,6 @@ namespace ts {
return parseUnionOrIntersectionType(SyntaxKind.UnionType, parseIntersectionTypeOrHigher, SyntaxKind.BarToken);
}
function parseConditionalTypeOrHigher(): TypeNode {
const type = parseUnionTypeOrHigher();
if (parseOptional(SyntaxKind.ExtendsKeyword)) {
const node = <ConditionalTypeNode>createNode(SyntaxKind.ConditionalType, type.pos);
node.checkType = type;
node.extendsType = parseType();
parseExpected(SyntaxKind.QuestionToken);
node.trueType = parseType();
parseExpected(SyntaxKind.ColonToken);
node.falseType = parseType();
return finishNode(node);
}
return type;
}
function isStartOfFunctionType(): boolean {
if (token() === SyntaxKind.LessThanToken) {
return true;
@@ -2979,14 +2964,26 @@ namespace ts {
return doOutsideOfContext(NodeFlags.TypeExcludesFlags, parseTypeWorker);
}
function parseTypeWorker(): TypeNode {
function parseTypeWorker(noConditionalTypes?: boolean): TypeNode {
if (isStartOfFunctionType()) {
return parseFunctionOrConstructorType(SyntaxKind.FunctionType);
}
if (token() === SyntaxKind.NewKeyword) {
return parseFunctionOrConstructorType(SyntaxKind.ConstructorType);
}
return parseConditionalTypeOrHigher();
const type = parseUnionTypeOrHigher();
if (!noConditionalTypes && parseOptional(SyntaxKind.ExtendsKeyword)) {
const node = <ConditionalTypeNode>createNode(SyntaxKind.ConditionalType, type.pos);
node.checkType = type;
// The type following 'extends' is not permitted to be another conditional type
node.extendsType = parseTypeWorker(/*noConditionalTypes*/ true);
parseExpected(SyntaxKind.QuestionToken);
node.trueType = parseTypeWorker();
parseExpected(SyntaxKind.ColonToken);
node.falseType = parseTypeWorker();
return finishNode(node);
}
return type;
}
function parseTypeAnnotation(): TypeNode {