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Handle 'never' in return type inference

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This commit is contained in:
Anders Hejlsberg
2016-05-17 06:32:49 -07:00
parent c11d691d6f
commit aa028ca660
1 changed files with 8 additions and 5 deletions
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13
src/compiler/checker.ts
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@@ -11550,6 +11550,9 @@ namespace ts {
else {
const hasImplicitReturn = !!(func.flags & NodeFlags.HasImplicitReturn);
types = checkAndAggregateReturnExpressionTypes(<Block>func.body, contextualMapper, isAsync, hasImplicitReturn);
if (!types) {
return neverType;
}
if (types.length === 0) {
if (isAsync) {
// For an async function, the return type will not be void, but rather a Promise for void.
@@ -11558,12 +11561,9 @@ namespace ts {
error(func, Diagnostics.An_async_function_or_method_must_have_a_valid_awaitable_return_type);
return unknownType;
}
return promiseType;
}
else {
return hasImplicitReturn ? voidType : neverType;
}
return voidType;
}
}
// When yield/return statements are contextually typed we allow the return type to be a union type.
@@ -11643,7 +11643,7 @@ namespace ts {
// the native Promise<T> type by the caller.
type = checkAwaitedType(type, body.parent, Diagnostics.Return_expression_in_async_function_does_not_have_a_valid_callable_then_member);
}
if (!contains(aggregatedTypes, type)) {
if (type !== neverType && !contains(aggregatedTypes, type)) {
aggregatedTypes.push(type);
}
}
@@ -11651,6 +11651,9 @@ namespace ts {
hasOmittedExpressions = true;
}
});
if (aggregatedTypes.length === 0 && !hasOmittedExpressions && !hasImplicitReturn) {
return undefined;
}
if (strictNullChecks && aggregatedTypes.length && (hasOmittedExpressions || hasImplicitReturn)) {
if (!contains(aggregatedTypes, undefinedType)) {
aggregatedTypes.push(undefinedType);