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Optimize substitution types #50397

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merged 6 commits into from
Aug 26, 2022
Merged

Optimize substitution types #50397

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c09b7dc
Optimize substitution type infrastructure
ahejlsberg Aug 22, 2022
a4a9ede
Accept new baselines
ahejlsberg Aug 22, 2022
e73d268
Preserve instantiated substitution types for type variables
ahejlsberg Aug 22, 2022
f48a923
Restrictive type parameters should have no constraint
ahejlsberg Aug 22, 2022
95ea0ba
Fix issues from top100 test run
ahejlsberg Aug 25, 2022
aed9659
Accept new baselines
ahejlsberg Aug 25, 2022
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58 changes: 34 additions & 24 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -12344,7 +12344,7 @@ namespace ts {
return constraint && getBaseConstraint(constraint);
}
if (t.flags & TypeFlags.Substitution) {
return getBaseConstraint((t as SubstitutionType).substitute);
return getBaseConstraint(getSubstitutionIntersection(t as SubstitutionType));
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}
return t;
}
Expand Down Expand Up @@ -13881,22 +13881,28 @@ namespace ts {
return links.resolvedJSDocType;
}

function getSubstitutionType(baseType: Type, substitute: Type) {
if (substitute.flags & TypeFlags.AnyOrUnknown || substitute === baseType) {
function getSubstitutionType(baseType: Type, constraint: Type) {
if (constraint.flags & TypeFlags.AnyOrUnknown || constraint === baseType ||
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@DanielRosenwasser DanielRosenwasser Aug 22, 2022 •
edited
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constraint === baseType

Is this just when someone writes

T extends T ? TrueType<T> : FalseType<T>

?

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I presume so. The check was already there.

baseType.flags & TypeFlags.Substitution && (baseType as SubstitutionType).constraint === constraint ||
!isGenericType(baseType) && !isGenericType(constraint)) {
return baseType;
}
const id = `${getTypeId(baseType)}>${getTypeId(substitute)}`;
const id = `${getTypeId(baseType)}>${getTypeId(constraint)}`;
const cached = substitutionTypes.get(id);
if (cached) {
return cached;
}
const result = createType(TypeFlags.Substitution) as SubstitutionType;
result.baseType = baseType;
result.substitute = substitute;
result.constraint = constraint;
substitutionTypes.set(id, result);
return result;
}

function getSubstitutionIntersection(substitutionType: SubstitutionType) {
return getIntersectionType([substitutionType.constraint, substitutionType.baseType]);
}

function isUnaryTupleTypeNode(node: TypeNode) {
return node.kind === SyntaxKind.TupleType && (node as TupleTypeNode).elements.length === 1;
}
Expand Down Expand Up @@ -13941,7 +13947,7 @@ namespace ts {
}
node = parent;
}
return constraints ? getSubstitutionType(type, getIntersectionType(append(constraints, type))) : type;
return constraints ? getSubstitutionType(type, getIntersectionType(constraints)) : type;
}

function isJSDocTypeReference(node: Node): node is TypeReferenceNode {
Expand Down Expand Up @@ -15341,7 +15347,7 @@ namespace ts {
type.flags & TypeFlags.Conditional ? (type as ConditionalType).root.isDistributive && (type as ConditionalType).checkType === typeVariable :
type.flags & (TypeFlags.UnionOrIntersection | TypeFlags.TemplateLiteral) ? every((type as UnionOrIntersectionType | TemplateLiteralType).types, isDistributive) :
type.flags & TypeFlags.IndexedAccess ? isDistributive((type as IndexedAccessType).objectType) && isDistributive((type as IndexedAccessType).indexType) :
type.flags & TypeFlags.Substitution ? isDistributive((type as SubstitutionType).substitute) :
type.flags & TypeFlags.Substitution ? isDistributive((type as SubstitutionType).baseType) && isDistributive((type as SubstitutionType).constraint):
type.flags & TypeFlags.StringMapping ? isDistributive((type as StringMappingType).type) :
false;
}
Expand Down Expand Up @@ -15861,7 +15867,7 @@ namespace ts {
if (type.flags & TypeFlags.Substitution) {
if (!((type as SubstitutionType).objectFlags & ObjectFlags.IsGenericTypeComputed)) {
(type as SubstitutionType).objectFlags |= ObjectFlags.IsGenericTypeComputed |
getGenericObjectFlags((type as SubstitutionType).substitute) | getGenericObjectFlags((type as SubstitutionType).baseType);
getGenericObjectFlags((type as SubstitutionType).baseType) | getGenericObjectFlags((type as SubstitutionType).constraint);
}
return (type as SubstitutionType).objectFlags & ObjectFlags.IsGenericType;
}
Expand Down Expand Up @@ -17018,9 +17024,9 @@ namespace ts {
}
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I think you mentioned it in person, but remind me again: Why does this need to be noConstraintType? AFAIK, noConstraintTypeshould mostly just be used as a marker to makegetBaseConstraintOfTypereturnundefined, but a type parameter constrained to unknownand a type parameter without a constraint are supposed to be functionally identical nowadays. So if this change was required somewhere, I think it implies something is subtly broken. In any case, we should probably makenoConstraintTypeanunknown` variant at some point (since it's still an empty object), even if it's never supposed to actually be used as a type.

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@ahejlsberg ahejlsberg Aug 26, 2022 •
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The one difference I ran into is in getConstraintOfDistributiveConditionalType. It does nothing for type parameters declared without a constraint, but applies a distributive conditional type to a declared type parameter constraint, even if that constraint is unknown. Changing this would definitely be a breaking change.

Making matters worse, for a restrictive type parameter we used to jam in an unknown constraint even for a type parameter declared without a constraint--which effectively changed the observed constraint for a distributive conditional type.

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Ew, icky. Distributive constraints behaving differently for T vs T extends unknown is definitely pretty bad - do we know which direction's behavior is better? Given the direction of this PR, I'm led to think we should adopt the unconstrained T behavior for a T extends unknown.


function getRestrictiveTypeParameter(tp: TypeParameter) {
return tp.constraint === unknownType ? tp : tp.restrictiveInstantiation || (
return tp.constraint === noConstraintType ? tp : tp.restrictiveInstantiation || (
tp.restrictiveInstantiation = createTypeParameter(tp.symbol),
(tp.restrictiveInstantiation as TypeParameter).constraint = unknownType,
(tp.restrictiveInstantiation as TypeParameter).constraint = noConstraintType,
tp.restrictiveInstantiation
);
}
Expand Down Expand Up @@ -17407,17 +17413,17 @@ namespace ts {
return getConditionalTypeInstantiation(type as ConditionalType, combineTypeMappers((type as ConditionalType).mapper, mapper), aliasSymbol, aliasTypeArguments);
}
if (flags & TypeFlags.Substitution) {
const maybeVariable = instantiateType((type as SubstitutionType).baseType, mapper);
if (maybeVariable.flags & TypeFlags.TypeVariable) {
return getSubstitutionType(maybeVariable as TypeVariable, instantiateType((type as SubstitutionType).substitute, mapper));
}
else {
const sub = instantiateType((type as SubstitutionType).substitute, mapper);
if (sub.flags & TypeFlags.AnyOrUnknown || isTypeAssignableTo(getRestrictiveInstantiation(maybeVariable), getRestrictiveInstantiation(sub))) {
return maybeVariable;
}
return sub;
}
const newBaseType = instantiateType((type as SubstitutionType).baseType, mapper);
const newConstraint = instantiateType((type as SubstitutionType).constraint, mapper);
// A substitution type originates in the true branch of a conditional type and can be resolved
// to just the base type in the same cases as the conditional type resolves to its true branch
// (because the base type is then known to satisfy the constraint).
if (newConstraint.flags & TypeFlags.AnyOrUnknown ||
!isGenericType(newBaseType) && !isGenericType(newConstraint) ||
isTypeAssignableTo(getRestrictiveInstantiation(newBaseType), getRestrictiveInstantiation(newConstraint))) {
return newBaseType;
}
return getSubstitutionType(newBaseType, newConstraint);
}
return type;
}
Expand Down Expand Up @@ -18456,7 +18462,7 @@ namespace ts {
const t = isFreshLiteralType(type) ? (type as FreshableType).regularType :
getObjectFlags(type) & ObjectFlags.Reference ? (type as TypeReference).node ? createTypeReference((type as TypeReference).target, getTypeArguments(type as TypeReference)) : getSingleBaseForNonAugmentingSubtype(type) || type :
type.flags & TypeFlags.UnionOrIntersection ? getNormalizedUnionOrIntersectionType(type as UnionOrIntersectionType, writing) :
type.flags & TypeFlags.Substitution ? writing ? (type as SubstitutionType).baseType : (type as SubstitutionType).substitute :
type.flags & TypeFlags.Substitution ? writing ? (type as SubstitutionType).baseType : getSubstitutionIntersection(type as SubstitutionType) :
type.flags & TypeFlags.Simplifiable ? getSimplifiedType(type, writing) :
type;
if (t === type) return t;
Expand Down Expand Up @@ -19539,7 +19545,11 @@ namespace ts {
}
}
if (sourceFlags & TypeFlags.Substitution) {
return isRelatedTo((source as SubstitutionType).substitute, (target as SubstitutionType).substitute, RecursionFlags.Both, /*reportErrors*/ false);
if (result = isRelatedTo((source as SubstitutionType).baseType, (target as SubstitutionType).baseType, RecursionFlags.Both, /*reportErrors*/ false)) {
if (result &= isRelatedTo((source as SubstitutionType).constraint, (target as SubstitutionType).constraint, RecursionFlags.Both, /*reportErrors*/ false)) {
return result;
}
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This is a meaningful break in behavior, right? Previously type FilterNever<T> = T extends never ? T : never would have allowed FilterNever<A> to be assignable to FilterNever<B> (where A and B are both type parameters), since T & never is just never, and eliminated the need to relate the type parameter part, no?

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This is in the code path for identityRelation, so hardly matters. In your particular example the types wouldn't relate anyway because the type parameters aren't identical.

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That's what would technically make it a break, right? Previously this related substitutions only, so A sub A & never and B sub B & never both looked identically like never?

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Yeah, that's true. But they definitely shouldn't be related, so I guess this fixes a bug as well.

}
}
if (!(sourceFlags & TypeFlags.Object)) {
return Ternary.False;
Expand Down Expand Up @@ -22677,7 +22687,7 @@ namespace ts {
}
else if (source.flags & TypeFlags.Substitution) {
inferFromTypes((source as SubstitutionType).baseType, target);
inferWithPriority((source as SubstitutionType).substitute, target, InferencePriority.SubstituteSource); // Make substitute inference at a lower priority
inferWithPriority(getSubstitutionIntersection(source as SubstitutionType), target, InferencePriority.SubstituteSource); // Make substitute inference at a lower priority
}
else if (target.flags & TypeFlags.Conditional) {
invokeOnce(source, target, inferToConditionalType);
Expand Down
2 changes: 1 addition & 1 deletion src/compiler/tracing.ts
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Expand Up @@ -253,7 +253,7 @@ namespace ts { // eslint-disable-line one-namespace-per-file
const substitutionType = type as SubstitutionType;
substitutionProperties = {
substitutionBaseType: substitutionType.baseType?.id,
substituteType: substitutionType.substitute?.id,
constraintType: substitutionType.constraint?.id,
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};
}

Expand Down
4 changes: 2 additions & 2 deletions src/compiler/types.ts
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Expand Up @@ -6077,8 +6077,8 @@ namespace ts {
// types disappear upon instantiation (just like type parameters).
export interface SubstitutionType extends InstantiableType {
objectFlags: ObjectFlags;
baseType: Type; // Target type
substitute: Type; // Type to substitute for type parameter
baseType: Type; // Target type
constraint: Type; // Constraint that target type is known to satisfy
}

/* @internal */
Expand Down
2 changes: 1 addition & 1 deletion tests/baselines/reference/api/tsserverlibrary.d.ts
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Expand Up @@ -2832,7 +2832,7 @@ declare namespace ts {
export interface SubstitutionType extends InstantiableType {
objectFlags: ObjectFlags;
baseType: Type;
substitute: Type;
constraint: Type;
}
export enum SignatureKind {
Call = 0,
Expand Down
2 changes: 1 addition & 1 deletion tests/baselines/reference/api/typescript.d.ts
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Expand Up @@ -2832,7 +2832,7 @@ declare namespace ts {
export interface SubstitutionType extends InstantiableType {
objectFlags: ObjectFlags;
baseType: Type;
substitute: Type;
constraint: Type;
}
export enum SignatureKind {
Call = 0,
Expand Down
6 changes: 3 additions & 3 deletions tests/baselines/reference/callOfConditionalTypeWithConcreteBranches.types
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Expand Up @@ -64,11 +64,11 @@ function fn2<T>(arg: Q2<T>) {
arg(arg => useT(arg));
>arg(arg => useT(arg)) : void
>arg : Q2<T>
>arg => useT(arg) : (arg: T & number) => void
>arg : T & number
>arg => useT(arg) : (arg: number) => void
>arg : number
>useT(arg) : void
>useT : (_arg: T) => void
>arg : T & number
>arg : number
}
// Legal invocations are not problematic
fn2<string | number>(m => m(42));
Expand Down
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