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Add 'never' type #8652

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Merged
ahejlsberg merged 6 commits into from
May 18, 2016
Merged

Add 'never' type #8652

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c11d691
Introduce 'never' type
ahejlsberg May 17, 2016
aa028ca
Handle 'never' in return type inference
ahejlsberg May 17, 2016
be7e2a8
Make 'never' an intrinsic type
ahejlsberg May 17, 2016
e028c0f
Accepting new baselines
ahejlsberg May 17, 2016
88d7f23
Add additional error checking
ahejlsberg May 17, 2016
bfd8704
Adding tests
ahejlsberg May 17, 2016
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Handle 'never' in return type inference
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@ahejlsberg
ahejlsberg committed May 17, 2016
commit aa028ca66054d4248a45593520a4bda7e70e37d5
13 changes: 8 additions & 5 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand All @@ -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.
Expand Down Expand Up @@ -11643,14 +11643,17 @@ 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);
}
}
else {
hasOmittedExpressions = true;
}
});
if (aggregatedTypes.length === 0 && !hasOmittedExpressions && !hasImplicitReturn) {
return undefined;
}
if (strictNullChecks && aggregatedTypes.length && (hasOmittedExpressions || hasImplicitReturn)) {
if (!contains(aggregatedTypes, undefinedType)) {
aggregatedTypes.push(undefinedType);
Expand Down