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Exclude primitive types from union subtype reduction in most cases
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@ahejlsberg
ahejlsberg committed Jan 14, 2021
1 parent c456bbd commit b46ca71
Showing 1 changed file with 46 additions and 60 deletions.
106 changes: 46 additions & 60 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -13255,54 +13255,40 @@ namespace ts {
return includes;
}

function isSetOfLiteralsFromSameEnum(types: readonly Type[]): boolean {
const first = types[0];
if (first.flags & TypeFlags.EnumLiteral) {
const firstEnum = getParentOfSymbol(first.symbol);
for (let i = 1; i < types.length; i++) {
const other = types[i];
if (!(other.flags & TypeFlags.EnumLiteral) || (firstEnum !== getParentOfSymbol(other.symbol))) {
return false;
}
}
return true;
}

return false;
}

function removeSubtypes(types: Type[], primitivesOnly: boolean): boolean {
const len = types.length;
if (len === 0 || isSetOfLiteralsFromSameEnum(types)) {
return true;
}
function removeSubtypes(types: Type[]): boolean {
// We assume that redundant primitive types have already been removed from the types array and that there
// are no any and unknown types in the array. Thus, the only possible supertypes for primitive types are empty
// object types, and if none of those are present we can exclude primitive types from the subtype check.
const hasEmptyObject = some(types, t => !!(t.flags & TypeFlags.Object) && !isGenericMappedType(t) && isEmptyResolvedType(resolveStructuredTypeMembers(<ObjectType>t)));
let len = types.length;
let i = len;
let count = 0;
while (i > 0) {
i--;
const source = types[i];
for (const target of types) {
if (source !== target) {
if (count === 100000) {
// After 100000 subtype checks we estimate the remaining amount of work by assuming the
// same ratio of checks per element. If the estimated number of remaining type checks is
// greater than an upper limit we deem the union type too complex to represent. The
// upper limit is 25M for unions of primitives only, and 1M otherwise. This for example
// caps union types at 5000 unique literal types and 1000 unique object types.
const estimatedCount = (count / (len - i)) * len;
if (estimatedCount > (primitivesOnly ? 25000000 : 1000000)) {
tracing.instant(tracing.Phase.CheckTypes, "removeSubtypes_DepthLimit", { typeIds: types.map(t => t.id) });
error(currentNode, Diagnostics.Expression_produces_a_union_type_that_is_too_complex_to_represent);
return false;
if (hasEmptyObject || source.flags & TypeFlags.StructuredOrInstantiable) {
for (const target of types) {
if (source !== target) {
if (count === 100000) {
// After 100000 subtype checks we estimate the remaining amount of work by assuming the
// same ratio of checks per element. If the estimated number of remaining type checks is
// greater than 1M we deem the union type too complex to represent. This for example
// caps union types at 1000 unique object types.
const estimatedCount = (count / (len - i)) * len;
if (estimatedCount > 1000000) {
tracing.instant(tracing.Phase.CheckTypes, "removeSubtypes_DepthLimit", { typeIds: types.map(t => t.id) });
error(currentNode, Diagnostics.Expression_produces_a_union_type_that_is_too_complex_to_represent);
return false;
}
}
count++;
if (isTypeRelatedTo(source, target, strictSubtypeRelation) && (
!(getObjectFlags(getTargetType(source)) & ObjectFlags.Class) ||
!(getObjectFlags(getTargetType(target)) & ObjectFlags.Class) ||
isTypeDerivedFrom(source, target))) {
orderedRemoveItemAt(types, i);
break;
}
}
count++;
if (isTypeRelatedTo(source, target, strictSubtypeRelation) && (
!(getObjectFlags(getTargetType(source)) & ObjectFlags.Class) ||
!(getObjectFlags(getTargetType(target)) & ObjectFlags.Class) ||
isTypeDerivedFrom(source, target))) {
orderedRemoveItemAt(types, i);
break;
}
}
}
Expand All @@ -13315,11 +13301,13 @@ namespace ts {
while (i > 0) {
i--;
const t = types[i];
const flags = t.flags;
const remove =
t.flags & TypeFlags.StringLikeLiteral && includes & TypeFlags.String ||
t.flags & TypeFlags.NumberLiteral && includes & TypeFlags.Number ||
t.flags & TypeFlags.BigIntLiteral && includes & TypeFlags.BigInt ||
t.flags & TypeFlags.UniqueESSymbol && includes & TypeFlags.ESSymbol ||
flags & TypeFlags.StringLikeLiteral && includes & TypeFlags.String ||
flags & TypeFlags.NumberLiteral && includes & TypeFlags.Number ||
flags & TypeFlags.BigIntLiteral && includes & TypeFlags.BigInt ||
flags & TypeFlags.UniqueESSymbol && includes & TypeFlags.ESSymbol ||
flags & TypeFlags.Undefined && includes & TypeFlags.Void ||
isFreshLiteralType(t) && containsType(types, (<LiteralType>t).regularType);
if (remove) {
orderedRemoveItemAt(types, i);
Expand Down Expand Up @@ -13385,20 +13373,18 @@ namespace ts {
if (includes & TypeFlags.AnyOrUnknown) {
return includes & TypeFlags.Any ? includes & TypeFlags.IncludesWildcard ? wildcardType : anyType : unknownType;
}
switch (unionReduction) {
case UnionReduction.Literal:
if (includes & (TypeFlags.FreshableLiteral | TypeFlags.UniqueESSymbol)) {
removeRedundantLiteralTypes(typeSet, includes);
}
if (includes & TypeFlags.StringLiteral && includes & TypeFlags.TemplateLiteral) {
removeStringLiteralsMatchedByTemplateLiterals(typeSet);
}
break;
case UnionReduction.Subtype:
if (!removeSubtypes(typeSet, !(includes & TypeFlags.IncludesStructuredOrInstantiable))) {
return errorType;
}
break;
if (unionReduction & (UnionReduction.Literal | UnionReduction.Subtype)) {
if (includes & (TypeFlags.FreshableLiteral | TypeFlags.UniqueESSymbol) || includes & TypeFlags.Void && includes & TypeFlags.Undefined) {
removeRedundantLiteralTypes(typeSet, includes);
}
if (includes & TypeFlags.StringLiteral && includes & TypeFlags.TemplateLiteral) {
removeStringLiteralsMatchedByTemplateLiterals(typeSet);
}
}
if (unionReduction & UnionReduction.Subtype) {
if (!removeSubtypes(typeSet)) {
return errorType;
}
}
if (typeSet.length === 0) {
return includes & TypeFlags.Null ? includes & TypeFlags.IncludesNonWideningType ? nullType : nullWideningType :
Expand Down

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