microsoft · Andarist · Mar 29, 2025 · Mar 29, 2025 · Mar 29, 2025 · Mar 29, 2025
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -2316,6 +2316,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     var inferenceContexts: (InferenceContext | undefined)[] = [];
     var inferenceContextCount = 0;
 
+    var activeTypeMappers: TypeMapper[] = [];
+    var activeTypeMappersCaches: Map<string, Type>[] = [];
+    var activeTypeMappersCount = 0;
+
     var emptyStringType = getStringLiteralType("");
     var zeroType = getNumberLiteralType(0);
     var zeroBigIntType = getBigIntLiteralType({ negative: false, base10Value: "0" });
@@ -20371,10 +20375,26 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             error(currentNode, Diagnostics.Type_instantiation_is_excessively_deep_and_possibly_infinite);
             return errorType;
         }
+        const index = findActiveMapper(mapper);
+        if (index === -1) {
+            pushActiveMapper(mapper);
+        }
+        const key = type.id + getAliasId(aliasSymbol, aliasTypeArguments);
+        const mapperCache = activeTypeMappersCaches[index !== -1 ? index : activeTypeMappersCount - 1];
+        const cached = mapperCache.get(key);
+        if (cached) {
+            return cached;
+        }
         totalInstantiationCount++;
         instantiationCount++;
         instantiationDepth++;
         const result = instantiateTypeWorker(type, mapper, aliasSymbol, aliasTypeArguments);
+        if (index === -1) {
+            popActiveMapper();
+        }
+        else {
+            mapperCache.set(key, result);
+        }
         instantiationDepth--;
         return result;
     }
@@ -26947,6 +26967,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     inference.inferredType = fallbackType && context.compareTypes(fallbackType, getTypeWithThisArgument(instantiatedConstraint, fallbackType)) ? fallbackType : instantiatedConstraint;
                 }
             }
+            clearActiveMapperCaches();
         }
 
         return inference.inferredType;
@@ -32163,6 +32184,31 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
     }
 
+    function pushActiveMapper(mapper: TypeMapper) {
+        activeTypeMappers[activeTypeMappersCount] = mapper;
+        activeTypeMappersCaches[activeTypeMappersCount] = new Map();
+        activeTypeMappersCount++;
+    }
+
+    function popActiveMapper() {
+        activeTypeMappersCount--;
+    }
+
+    function findActiveMapper(mapper: TypeMapper) {
+        for (let i = activeTypeMappersCount - 1; i >= 0; i--) {
+            if (mapper === activeTypeMappers[i]) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    function clearActiveMapperCaches() {
+        for (let i = activeTypeMappersCount - 1; i >= 0; i--) {
+            activeTypeMappersCaches[i].clear();
+        }
+    }
+
     function getContextualImportAttributeType(node: ImportAttribute) {
         return getTypeOfPropertyOfContextualType(getGlobalImportAttributesType(/*reportErrors*/ false), getNameFromImportAttribute(node));
     }

diff --git a/tests/baselines/reference/callsOnComplexSignatures.types b/tests/baselines/reference/callsOnComplexSignatures.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 2,500
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === callsOnComplexSignatures.tsx ===

diff --git a/tests/baselines/reference/checkJsxChildrenCanBeTupleType.types b/tests/baselines/reference/checkJsxChildrenCanBeTupleType.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 2,500
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === checkJsxChildrenCanBeTupleType.tsx ===

diff --git a/tests/baselines/reference/checkJsxChildrenProperty16.types b/tests/baselines/reference/checkJsxChildrenProperty16.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 2,500
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === checkJsxChildrenProperty16.tsx ===

diff --git a/tests/baselines/reference/checkJsxUnionSFXContextualTypeInferredCorrectly.types b/tests/baselines/reference/checkJsxUnionSFXContextualTypeInferredCorrectly.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 2,500
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === checkJsxUnionSFXContextualTypeInferredCorrectly.tsx ===

diff --git a/tests/baselines/reference/circularBaseConstraint.types b/tests/baselines/reference/circularBaseConstraint.types
@@ -1,8 +1,5 @@
 //// [tests/cases/compiler/circularBaseConstraint.ts] ////
 
-=== Performance Stats ===
-Instantiation count: 2,500
-
 === circularBaseConstraint.ts ===
 // Repro from #54610
 

diff --git a/tests/baselines/reference/circularlySimplifyingConditionalTypesNoCrash.types b/tests/baselines/reference/circularlySimplifyingConditionalTypesNoCrash.types
@@ -1,8 +1,5 @@
 //// [tests/cases/compiler/circularlySimplifyingConditionalTypesNoCrash.ts] ////
 
-=== Performance Stats ===
-Instantiation count: 2,500
-
 === circularlySimplifyingConditionalTypesNoCrash.ts ===
 type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;
 >Omit : Omit<T, K>

diff --git a/...reference/conditionalTypeDiscriminatingLargeUnionRegularTypeFetchingSpeedReasonable.types b/...reference/conditionalTypeDiscriminatingLargeUnionRegularTypeFetchingSpeedReasonable.types
@@ -4,7 +4,7 @@
 Strict subtype cache: 2,500
 Assignability cache: 10,000
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 
 === conditionalTypeDiscriminatingLargeUnionRegularTypeFetchingSpeedReasonable.ts ===
 type BigUnion =

diff --git a/tests/baselines/reference/conditionalTypeDoesntSpinForever.types b/tests/baselines/reference/conditionalTypeDoesntSpinForever.types
@@ -2,7 +2,7 @@
 
 === Performance Stats ===
 Type Count: 1,000
-Instantiation count: 2,500 -> 5,000
+Instantiation count: 2,500
 
 === conditionalTypeDoesntSpinForever.ts ===
 // A *self-contained* demonstration of the problem follows...

diff --git a/tests/baselines/reference/conditionalTypeVarianceBigArrayConstraintsPerformance.types b/tests/baselines/reference/conditionalTypeVarianceBigArrayConstraintsPerformance.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 1,000
 Type Count: 5,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === conditionalTypeVarianceBigArrayConstraintsPerformance.ts ===

diff --git a/tests/baselines/reference/conditionalTypes1.types b/tests/baselines/reference/conditionalTypes1.types
@@ -1,8 +1,5 @@
 //// [tests/cases/conformance/types/conditional/conditionalTypes1.ts] ////
 
-=== Performance Stats ===
-Instantiation count: 1,000
-
 === conditionalTypes1.ts ===
 type T00 = Exclude<"a" | "b" | "c" | "d", "a" | "c" | "f">;  // "b" | "d"
 >T00 : T00

diff --git a/tests/baselines/reference/contextualParameterAndSelfReferentialConstraint1.symbols b/tests/baselines/reference/contextualParameterAndSelfReferentialConstraint1.symbols
@@ -0,0 +1,98 @@
+//// [tests/cases/compiler/contextualParameterAndSelfReferentialConstraint1.ts] ////
+
+=== contextualParameterAndSelfReferentialConstraint1.ts ===
+type NoExcessProperties<T, U> = T & {
+>NoExcessProperties : Symbol(NoExcessProperties, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 0))
+>T : Symbol(T, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 24))
+>U : Symbol(U, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 26))
+>T : Symbol(T, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 24))
+
+  readonly [K in Exclude<keyof U, keyof T>]: never;
+>K : Symbol(K, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 1, 12))
+>Exclude : Symbol(Exclude, Decl(lib.es5.d.ts, --, --))
+>U : Symbol(U, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 26))
+>T : Symbol(T, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 24))
+
+};
+
+interface Effect<out A> {
+>Effect : Symbol(Effect, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 2, 2))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 4, 17))
+
+  readonly EffectTypeId: {
+>EffectTypeId : Symbol(Effect.EffectTypeId, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 4, 25))
+
+    readonly _A: (_: never) => A;
+>_A : Symbol(_A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 5, 26))
+>_ : Symbol(_, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 6, 18))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 4, 17))
+
+  };
+}
+
+declare function pipe<A, B>(a: A, ab: (a: A) => B): B;
+>pipe : Symbol(pipe, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 8, 1))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 22))
+>B : Symbol(B, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 24))
+>a : Symbol(a, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 28))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 22))
+>ab : Symbol(ab, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 33))
+>a : Symbol(a, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 39))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 22))
+>B : Symbol(B, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 24))
+>B : Symbol(B, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 24))
+
+interface RepeatOptions<A> {
+>RepeatOptions : Symbol(RepeatOptions, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 54))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 12, 24))
+
+  until?: (_: A) => boolean;
+>until : Symbol(RepeatOptions.until, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 12, 28))
+>_ : Symbol(_, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 13, 11))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 12, 24))
+}
+
+declare const repeat: {
+>repeat : Symbol(repeat, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 16, 13))
+
+  <O extends NoExcessProperties<RepeatOptions<A>, O>, A>(
+>O : Symbol(O, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 3))
+>NoExcessProperties : Symbol(NoExcessProperties, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 0, 0))
+>RepeatOptions : Symbol(RepeatOptions, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 10, 54))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 53))
+>O : Symbol(O, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 3))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 53))
+
+    options: O,
+>options : Symbol(options, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 57))
+>O : Symbol(O, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 3))
+
+  ): (self: Effect<A>) => Effect<A>;
+>self : Symbol(self, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 19, 6))
+>Effect : Symbol(Effect, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 2, 2))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 53))
+>Effect : Symbol(Effect, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 2, 2))
+>A : Symbol(A, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 17, 53))
+
+};
+
+pipe(
+>pipe : Symbol(pipe, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 8, 1))
+
+  {} as Effect<boolean>,
+>Effect : Symbol(Effect, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 2, 2))
+
+  repeat({
+>repeat : Symbol(repeat, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 16, 13))
+
+    until: (x) => {
+>until : Symbol(until, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 24, 10))
+>x : Symbol(x, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 25, 12))
+
+      return x; // boolean
+>x : Symbol(x, Decl(contextualParameterAndSelfReferentialConstraint1.ts, 25, 12))
+
+    },
+  }),
+);
+
diff --git a/tests/baselines/reference/contextualParameterAndSelfReferentialConstraint1.types b/tests/baselines/reference/contextualParameterAndSelfReferentialConstraint1.types
@@ -0,0 +1,93 @@
+//// [tests/cases/compiler/contextualParameterAndSelfReferentialConstraint1.ts] ////
+
+=== contextualParameterAndSelfReferentialConstraint1.ts ===
+type NoExcessProperties<T, U> = T & {
+>NoExcessProperties : NoExcessProperties<T, U>
+>                   : ^^^^^^^^^^^^^^^^^^^^^^^^
+
+  readonly [K in Exclude<keyof U, keyof T>]: never;
+};
+
+interface Effect<out A> {
+  readonly EffectTypeId: {
+>EffectTypeId : { readonly _A: (_: never) => A; }
+>             : ^^^^^^^^^^^^^^^               ^^^
+
+    readonly _A: (_: never) => A;
+>_A : (_: never) => A
+>   : ^ ^^     ^^^^^ 
+>_ : never
+>  : ^^^^^
+
+  };
+}
+
+declare function pipe<A, B>(a: A, ab: (a: A) => B): B;
+>pipe : <A, B>(a: A, ab: (a: A) => B) => B
+>     : ^ ^^ ^^ ^^ ^^  ^^           ^^^^^ 
+>a : A
+>  : ^
+>ab : (a: A) => B
+>   : ^ ^^ ^^^^^ 
+>a : A
+>  : ^
+
+interface RepeatOptions<A> {
+  until?: (_: A) => boolean;
+>until : ((_: A) => boolean) | undefined
+>      : ^^ ^^ ^^^^^       ^^^^^^^^^^^^^
+>_ : A
+>  : ^
+}
+
+declare const repeat: {
+>repeat : <O extends NoExcessProperties<RepeatOptions<A>, O>, A>(options: O) => (self: Effect<A>) => Effect<A>
+>       : ^ ^^^^^^^^^                                       ^^ ^^       ^^ ^^^^^                              
+
+  <O extends NoExcessProperties<RepeatOptions<A>, O>, A>(
+    options: O,
+>options : O
+>        : ^
+
+  ): (self: Effect<A>) => Effect<A>;
+>self : Effect<A>
+>     : ^^^^^^^^^
+
+};
+
+pipe(
+>pipe(  {} as Effect<boolean>,  repeat({    until: (x) => {      return x; // boolean    },  }),) : Effect<boolean>
+>                                                                                                 : ^^^^^^^^^^^^^^^
+>pipe : <A, B>(a: A, ab: (a: A) => B) => B
+>     : ^ ^^ ^^ ^^ ^^  ^^           ^^^^^ 
+
+  {} as Effect<boolean>,
+>{} as Effect<boolean> : Effect<boolean>
+>                      : ^^^^^^^^^^^^^^^
+>{} : {}
+>   : ^^
+
+  repeat({
+>repeat({    until: (x) => {      return x; // boolean    },  }) : (self: Effect<boolean>) => Effect<boolean>
+>                                                                : ^    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+>repeat : <O extends NoExcessProperties<RepeatOptions<A>, O>, A>(options: O) => (self: Effect<A>) => Effect<A>
+>       : ^ ^^^^^^^^^                                       ^^ ^^       ^^ ^^^^^                              
+>{    until: (x) => {      return x; // boolean    },  } : { until: (x: boolean) => boolean; }
+>                                                        : ^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^
+
+    until: (x) => {
+>until : (x: boolean) => boolean
+>      : ^ ^^^^^^^^^^^^^^^^^^^^^
+>(x) => {      return x; // boolean    } : (x: boolean) => boolean
+>                                        : ^ ^^^^^^^^^^^^^^^^^^^^^
+>x : boolean
+>  : ^^^^^^^
+
+      return x; // boolean
+>x : boolean
+>  : ^^^^^^^
+
+    },
+  }),
+);
+
diff --git a/tests/baselines/reference/contextuallyTypedJsxChildren.types b/tests/baselines/reference/contextuallyTypedJsxChildren.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 2,500
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === contextuallyTypedJsxChildren.tsx ===

diff --git a/tests/baselines/reference/controlFlowOptionalChain3.types b/tests/baselines/reference/controlFlowOptionalChain3.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 2,500
 Type Count: 10,000
-Instantiation count: 100,000
+Instantiation count: 50,000
 Symbol count: 50,000
 
 === controlFlowOptionalChain3.tsx ===

diff --git a/tests/baselines/reference/declarationEmitHigherOrderRetainedGenerics.types b/tests/baselines/reference/declarationEmitHigherOrderRetainedGenerics.types
@@ -2,7 +2,7 @@
 
 === Performance Stats ===
 Type Count: 1,000
-Instantiation count: 2,500 -> 5,000
+Instantiation count: 2,500
 
 === declarationEmitHigherOrderRetainedGenerics.ts ===
 export interface TypeLambda {

diff --git a/...s/baselines/reference/declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.types b/...s/baselines/reference/declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.types
@@ -1,8 +1,5 @@
 //// [tests/cases/compiler/declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.ts] ////
 
-=== Performance Stats ===
-Instantiation count: 500 -> 1,000
-
 === declarationsWithRecursiveInternalTypesProduceUniqueTypeParams.ts ===
 // Note that both of the following have an `any` in their return type from where we bottom out the type printout
 // for having too many instances of the same symbol nesting.