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Sep 8, 2021
Merged

Tail recursive evaluation of conditional types #45711

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1610e19
Implement tail-recursion for conditional types and lower general inst…
ahejlsberg Sep 2, 2021
093f76a
Add tests
ahejlsberg Sep 3, 2021
a4224d6
Skip caching for tail recursive temporary conditional types
ahejlsberg Sep 4, 2021
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52 changes: 48 additions & 4 deletions src/compiler/checker.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -15223,10 +15223,18 @@ namespace ts {
function getConditionalType(root: ConditionalRoot, mapper: TypeMapper | undefined, aliasSymbol?: Symbol, aliasTypeArguments?: readonly Type[]): Type {
let result;
let extraTypes: Type[] | undefined;
let tailCount = 0;
// We loop here for an immediately nested conditional type in the false position, effectively treating
// types of the form 'A extends B ? X : C extends D ? Y : E extends F ? Z : ...' as a single construct for
// purposes of resolution. This means such types aren't subject to the instantiation depth limiter.
// purposes of resolution. We also loop here when resolution of a conditional type ends in resolution of
// another (or, through recursion, possibly the same) conditional type. In the potentially tail-recursive
// cases we increment the tail recursion counter and stop after 1000 iterations.
while (true) {
if (tailCount === 1000) {
error(currentNode, Diagnostics.Type_instantiation_is_excessively_deep_and_possibly_infinite);
result = errorType;
break;
}
const isUnwrapped = isTypicalNondistributiveConditional(root);
const checkType = instantiateType(unwrapNondistributiveConditionalTuple(root, getActualTypeVariable(root.checkType)), mapper);
const checkTypeInstantiable = isGenericType(checkType);
Expand Down Expand Up @@ -15270,6 +15278,9 @@ namespace ts {
root = newRoot;
continue;
}
if (canTailRecurse(falseType, mapper)) {
continue;
}
}
result = instantiateType(falseType, mapper);
break;
Expand All @@ -15280,7 +15291,12 @@ namespace ts {
// type Foo<T extends { x: any }> = T extends { x: string } ? string : number
// doesn't immediately resolve to 'string' instead of being deferred.
if (inferredExtendsType.flags & TypeFlags.AnyOrUnknown || isTypeAssignableTo(getRestrictiveInstantiation(checkType), getRestrictiveInstantiation(inferredExtendsType))) {
result = instantiateType(getTypeFromTypeNode(root.node.trueType), combinedMapper || mapper);
const trueType = getTypeFromTypeNode(root.node.trueType);
const trueMapper = combinedMapper || mapper;
if (canTailRecurse(trueType, trueMapper)) {
continue;
}
result = instantiateType(trueType, trueMapper);
break;
}
}
Expand All @@ -15296,6 +15312,34 @@ namespace ts {
break;
}
return extraTypes ? getUnionType(append(extraTypes, result)) : result;
// We tail-recurse for generic conditional types that (a) have not already been evaluated and cached, and
// (b) are non distributive, have a check type that is unaffected by instantiation, or have a non-union check
// type. Note that recursion is possible only through aliased conditional types, so we only increment the tail
// recursion counter for those.
function canTailRecurse(newType: Type, newMapper: TypeMapper | undefined) {
if (newType.flags & TypeFlags.Conditional && newMapper) {
const newRoot = (newType as ConditionalType).root;
if (newRoot.outerTypeParameters) {
const typeParamMapper = combineTypeMappers((newType as ConditionalType).mapper, newMapper);
const typeArguments = map(newRoot.outerTypeParameters, t => getMappedType(t, typeParamMapper));
if (!newRoot.instantiations!.get(getTypeListId(typeArguments))) {
const newRootMapper = createTypeMapper(newRoot.outerTypeParameters, typeArguments);
const newCheckType = newRoot.isDistributive ? getMappedType(newRoot.checkType, newRootMapper) : undefined;
if (!newCheckType || newCheckType === newRoot.checkType || !(newCheckType.flags & (TypeFlags.Union | TypeFlags.Never))) {
root = newRoot;
mapper = newRootMapper;
aliasSymbol = undefined;
aliasTypeArguments = undefined;
if (newRoot.aliasSymbol) {
tailCount++;
}
return true;
}
}
}
}
return false;
}
}

function getTrueTypeFromConditionalType(type: ConditionalType) {
Expand Down Expand Up @@ -16316,8 +16360,8 @@ namespace ts {
if (!couldContainTypeVariables(type)) {
return type;
}
if (instantiationDepth === 500 || instantiationCount >= 5000000) {
// We have reached 500 recursive type instantiations, or 5M type instantiations caused by the same statement
if (instantiationDepth === 100 || instantiationCount >= 5000000) {
// We have reached 100 recursive type instantiations, or 5M type instantiations caused by the same statement
// or expression. There is a very high likelyhood we're dealing with a combination of infinite generic types
// that perpetually generate new type identities, so we stop the recursion here by yielding the error type.
tracing?.instant(tracing.Phase.CheckTypes, "instantiateType_DepthLimit", { typeId: type.id, instantiationDepth, instantiationCount });
Expand Down
49 changes: 49 additions & 0 deletions tests/baselines/reference/tailRecursiveConditionalTypes.js
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@@ -0,0 +1,49 @@
//// [tailRecursiveConditionalTypes.ts]
type Trim<S extends string> =
S extends ` ${infer T}` ? Trim<T> :
S extends `${infer T} ` ? Trim<T> :
S;

type T10 = Trim<' hello '>;
type T11 = Trim<' hello '>;

type GetChars<S> = GetCharsRec<S, never>;
type GetCharsRec<S, Acc> =
S extends `${infer Char}${infer Rest}` ? GetCharsRec<Rest, Char | Acc> : Acc;

type T20 = GetChars<'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'>;

type Reverse<T> = any[] extends T ? T : ReverseRec<T, []>;
type ReverseRec<T, Acc extends unknown[]> =
T extends [infer Head, ...infer Tail] ? ReverseRec<Tail, [Head, ...Acc]> : Acc;

type T30 = Reverse<[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>;
type T31 = Reverse<string[]>;

type TupleOf<T, N extends number> = number extends N ? T[] : TupleOfRec<T, N, []>;
type TupleOfRec<T, N extends number, Acc extends unknown[]> =
Acc["length"] extends N ? Acc : TupleOfRec<T, N, [T, ...Acc]>;

type T40 = TupleOf<any, 200>;
type T41 = TupleOf<any, number>;


//// [tailRecursiveConditionalTypes.js]
"use strict";


//// [tailRecursiveConditionalTypes.d.ts]
declare type Trim<S extends string> = S extends ` ${infer T}` ? Trim<T> : S extends `${infer T} ` ? Trim<T> : S;
declare type T10 = Trim<' hello '>;
declare type T11 = Trim<' hello '>;
declare type GetChars<S> = GetCharsRec<S, never>;
declare type GetCharsRec<S, Acc> = S extends `${infer Char}${infer Rest}` ? GetCharsRec<Rest, Char | Acc> : Acc;
declare type T20 = GetChars<'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'>;
declare type Reverse<T> = any[] extends T ? T : ReverseRec<T, []>;
declare type ReverseRec<T, Acc extends unknown[]> = T extends [infer Head, ...infer Tail] ? ReverseRec<Tail, [Head, ...Acc]> : Acc;
declare type T30 = Reverse<[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>;
declare type T31 = Reverse<string[]>;
declare type TupleOf<T, N extends number> = number extends N ? T[] : TupleOfRec<T, N, []>;
declare type TupleOfRec<T, N extends number, Acc extends unknown[]> = Acc["length"] extends N ? Acc : TupleOfRec<T, N, [T, ...Acc]>;
declare type T40 = TupleOf<any, 200>;
declare type T41 = TupleOf<any, number>;
118 changes: 118 additions & 0 deletions tests/baselines/reference/tailRecursiveConditionalTypes.symbols
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@@ -0,0 +1,118 @@
=== tests/cases/compiler/tailRecursiveConditionalTypes.ts ===
type Trim<S extends string> =
>Trim : Symbol(Trim, Decl(tailRecursiveConditionalTypes.ts, 0, 0))
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 0, 10))

S extends ` ${infer T}` ? Trim<T> :
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 0, 10))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 1, 23))
>Trim : Symbol(Trim, Decl(tailRecursiveConditionalTypes.ts, 0, 0))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 1, 23))

S extends `${infer T} ` ? Trim<T> :
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 0, 10))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 2, 22))
>Trim : Symbol(Trim, Decl(tailRecursiveConditionalTypes.ts, 0, 0))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 2, 22))

S;
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 0, 10))

type T10 = Trim<' hello '>;
>T10 : Symbol(T10, Decl(tailRecursiveConditionalTypes.ts, 3, 6))
>Trim : Symbol(Trim, Decl(tailRecursiveConditionalTypes.ts, 0, 0))

type T11 = Trim<' hello '>;
>T11 : Symbol(T11, Decl(tailRecursiveConditionalTypes.ts, 5, 170))
>Trim : Symbol(Trim, Decl(tailRecursiveConditionalTypes.ts, 0, 0))

type GetChars<S> = GetCharsRec<S, never>;
>GetChars : Symbol(GetChars, Decl(tailRecursiveConditionalTypes.ts, 6, 170))
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 8, 14))
>GetCharsRec : Symbol(GetCharsRec, Decl(tailRecursiveConditionalTypes.ts, 8, 41))
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 8, 14))

type GetCharsRec<S, Acc> =
>GetCharsRec : Symbol(GetCharsRec, Decl(tailRecursiveConditionalTypes.ts, 8, 41))
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 9, 17))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 9, 19))

S extends `${infer Char}${infer Rest}` ? GetCharsRec<Rest, Char | Acc> : Acc;
>S : Symbol(S, Decl(tailRecursiveConditionalTypes.ts, 9, 17))
>Char : Symbol(Char, Decl(tailRecursiveConditionalTypes.ts, 10, 22))
>Rest : Symbol(Rest, Decl(tailRecursiveConditionalTypes.ts, 10, 35))
>GetCharsRec : Symbol(GetCharsRec, Decl(tailRecursiveConditionalTypes.ts, 8, 41))
>Rest : Symbol(Rest, Decl(tailRecursiveConditionalTypes.ts, 10, 35))
>Char : Symbol(Char, Decl(tailRecursiveConditionalTypes.ts, 10, 22))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 9, 19))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 9, 19))

type T20 = GetChars<'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'>;
>T20 : Symbol(T20, Decl(tailRecursiveConditionalTypes.ts, 10, 81))
>GetChars : Symbol(GetChars, Decl(tailRecursiveConditionalTypes.ts, 6, 170))

type Reverse<T> = any[] extends T ? T : ReverseRec<T, []>;
>Reverse : Symbol(Reverse, Decl(tailRecursiveConditionalTypes.ts, 12, 86))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 14, 13))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 14, 13))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 14, 13))
>ReverseRec : Symbol(ReverseRec, Decl(tailRecursiveConditionalTypes.ts, 14, 58))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 14, 13))

type ReverseRec<T, Acc extends unknown[]> =
>ReverseRec : Symbol(ReverseRec, Decl(tailRecursiveConditionalTypes.ts, 14, 58))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 15, 16))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 15, 18))

T extends [infer Head, ...infer Tail] ? ReverseRec<Tail, [Head, ...Acc]> : Acc;
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 15, 16))
>Head : Symbol(Head, Decl(tailRecursiveConditionalTypes.ts, 16, 20))
>Tail : Symbol(Tail, Decl(tailRecursiveConditionalTypes.ts, 16, 35))
>ReverseRec : Symbol(ReverseRec, Decl(tailRecursiveConditionalTypes.ts, 14, 58))
>Tail : Symbol(Tail, Decl(tailRecursiveConditionalTypes.ts, 16, 35))
>Head : Symbol(Head, Decl(tailRecursiveConditionalTypes.ts, 16, 20))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 15, 18))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 15, 18))

type T30 = Reverse<[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>;
>T30 : Symbol(T30, Decl(tailRecursiveConditionalTypes.ts, 16, 83))
>Reverse : Symbol(Reverse, Decl(tailRecursiveConditionalTypes.ts, 12, 86))

type T31 = Reverse<string[]>;
>T31 : Symbol(T31, Decl(tailRecursiveConditionalTypes.ts, 18, 171))
>Reverse : Symbol(Reverse, Decl(tailRecursiveConditionalTypes.ts, 12, 86))

type TupleOf<T, N extends number> = number extends N ? T[] : TupleOfRec<T, N, []>;
>TupleOf : Symbol(TupleOf, Decl(tailRecursiveConditionalTypes.ts, 19, 29))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 21, 13))
>N : Symbol(N, Decl(tailRecursiveConditionalTypes.ts, 21, 15))
>N : Symbol(N, Decl(tailRecursiveConditionalTypes.ts, 21, 15))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 21, 13))
>TupleOfRec : Symbol(TupleOfRec, Decl(tailRecursiveConditionalTypes.ts, 21, 82))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 21, 13))
>N : Symbol(N, Decl(tailRecursiveConditionalTypes.ts, 21, 15))

type TupleOfRec<T, N extends number, Acc extends unknown[]> =
>TupleOfRec : Symbol(TupleOfRec, Decl(tailRecursiveConditionalTypes.ts, 21, 82))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 22, 16))
>N : Symbol(N, Decl(tailRecursiveConditionalTypes.ts, 22, 18))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 22, 36))

Acc["length"] extends N ? Acc : TupleOfRec<T, N, [T, ...Acc]>;
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 22, 36))
>N : Symbol(N, Decl(tailRecursiveConditionalTypes.ts, 22, 18))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 22, 36))
>TupleOfRec : Symbol(TupleOfRec, Decl(tailRecursiveConditionalTypes.ts, 21, 82))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 22, 16))
>N : Symbol(N, Decl(tailRecursiveConditionalTypes.ts, 22, 18))
>T : Symbol(T, Decl(tailRecursiveConditionalTypes.ts, 22, 16))
>Acc : Symbol(Acc, Decl(tailRecursiveConditionalTypes.ts, 22, 36))

type T40 = TupleOf<any, 200>;
>T40 : Symbol(T40, Decl(tailRecursiveConditionalTypes.ts, 23, 66))
>TupleOf : Symbol(TupleOf, Decl(tailRecursiveConditionalTypes.ts, 19, 29))

type T41 = TupleOf<any, number>;
>T41 : Symbol(T41, Decl(tailRecursiveConditionalTypes.ts, 25, 29))
>TupleOf : Symbol(TupleOf, Decl(tailRecursiveConditionalTypes.ts, 19, 29))

53 changes: 53 additions & 0 deletions tests/baselines/reference/tailRecursiveConditionalTypes.types
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=== tests/cases/compiler/tailRecursiveConditionalTypes.ts ===
type Trim<S extends string> =
>Trim : Trim<S>

S extends ` ${infer T}` ? Trim<T> :
S extends `${infer T} ` ? Trim<T> :
S;

type T10 = Trim<' hello '>;
>T10 : "hello"

type T11 = Trim<' hello '>;
>T11 : "hello"

type GetChars<S> = GetCharsRec<S, never>;
>GetChars : GetChars<S>

type GetCharsRec<S, Acc> =
>GetCharsRec : GetCharsRec<S, Acc>

S extends `${infer Char}${infer Rest}` ? GetCharsRec<Rest, Char | Acc> : Acc;

type T20 = GetChars<'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'>;
>T20 : "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" | "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

type Reverse<T> = any[] extends T ? T : ReverseRec<T, []>;
>Reverse : Reverse<T>

type ReverseRec<T, Acc extends unknown[]> =
>ReverseRec : ReverseRec<T, Acc>

T extends [infer Head, ...infer Tail] ? ReverseRec<Tail, [Head, ...Acc]> : Acc;

type T30 = Reverse<[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]>;
>T30 : [9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

type T31 = Reverse<string[]>;
>T31 : string[]

type TupleOf<T, N extends number> = number extends N ? T[] : TupleOfRec<T, N, []>;
>TupleOf : TupleOf<T, N>

type TupleOfRec<T, N extends number, Acc extends unknown[]> =
>TupleOfRec : TupleOfRec<T, N, Acc>

Acc["length"] extends N ? Acc : TupleOfRec<T, N, [T, ...Acc]>;

type T40 = TupleOf<any, 200>;
>T40 : [any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any, any]

type T41 = TupleOf<any, number>;
>T41 : any[]

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