only disable cache on certain makeFunctionTypeMappers

microsoft · jakebailey · Jun 6, 2025 · Mar 29, 2025 · Mar 29, 2025 · Mar 29, 2025
commit b0f5c703072ab9ea97d73176f379014e2e28048d
diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
@@ -2101,6 +2101,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     var numericStringType = getTemplateLiteralType(["", ""], [numberType]); // The `${number}` type
 
     var restrictiveMapper: TypeMapper = makeFunctionTypeMapper(t => t.flags & TypeFlags.TypeParameter ? getRestrictiveTypeParameter(t as TypeParameter) : t, () => "(restrictive mapper)");
+    restrictiveMapper.instantiations = voidMap;
     var permissiveMapper: TypeMapper = makeFunctionTypeMapper(t => t.flags & TypeFlags.TypeParameter ? wildcardType : t, () => "(permissive mapper)");
     var uniqueLiteralType = createIntrinsicType(TypeFlags.Never, "never", /*objectFlags*/ undefined, "unique literal"); // `uniqueLiteralType` is a special `never` flagged by union reduction to behave as a literal
     var uniqueLiteralMapper: TypeMapper = makeFunctionTypeMapper(t => t.flags & TypeFlags.TypeParameter ? uniqueLiteralType : t, () => "(unique literal mapper)"); // replace all type parameters with the unique literal type (disregarding constraints)
@@ -2111,12 +2112,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
         return t;
     }, () => "(unmeasurable reporter)");
+    reportUnreliableMapper.instantiations = voidMap;
     var reportUnmeasurableMapper = makeFunctionTypeMapper(t => {
         if (outofbandVarianceMarkerHandler && (t === markerSuperType || t === markerSubType || t === markerOtherType)) {
             outofbandVarianceMarkerHandler(/*onlyUnreliable*/ false);
         }
         return t;
     }, () => "(unreliable reporter)");
+    reportUnmeasurableMapper.instantiations = voidMap;
 
     var emptyObjectType = createAnonymousType(/*symbol*/ undefined, emptySymbols, emptyArray, emptyArray, emptyArray);
     var emptyJsxObjectType = createAnonymousType(/*symbol*/ undefined, emptySymbols, emptyArray, emptyArray, emptyArray);
@@ -19961,9 +19964,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
     }
 
     function makeFunctionTypeMapper(func: (t: Type) => Type, debugInfo: () => string): TypeMapper {
-        const mapper = Debug.attachDebugPrototypeIfDebug({ kind: TypeMapKind.Function, func, debugInfo: Debug.isDebugging ? debugInfo : undefined });
-        mapper.instantiations = voidMap;
-        return mapper;
+        return Debug.attachDebugPrototypeIfDebug({ kind: TypeMapKind.Function, func, debugInfo: Debug.isDebugging ? debugInfo : undefined });
     }
 
     function makeDeferredTypeMapper(sources: readonly TypeParameter[], targets: (() => Type)[]) {

diff --git a/tests/baselines/reference/largeTupleTypes.types b/tests/baselines/reference/largeTupleTypes.types
@@ -3,7 +3,7 @@
 === Performance Stats ===
 Assignability cache: 1,000
 Type Count: 25,000
-Instantiation count: 50,000
+Instantiation count: 25,000
 Symbol count: 50,000
 
 === largeTupleTypes.ts ===

diff --git a/tests/baselines/reference/longObjectInstantiationChain1.errors.txt b/tests/baselines/reference/longObjectInstantiationChain1.errors.txt
@@ -1,16 +1,10 @@
 longObjectInstantiationChain1.ts(57,4): error TS2339: Property 'p51' does not exist on type 'merge<{ p1: number; }, { p2: number; }>'.
 longObjectInstantiationChain1.ts(62,4): error TS2339: Property 'p4' does not exist on type 'merge<merge<{ p1: number; }, { p2: number; }>, { p3: number; }>'.
-longObjectInstantiationChain1.ts(64,1): error TS2589: Type instantiation is excessively deep and possibly infinite.
-longObjectInstantiationChain1.ts(65,1): error TS2589: Type instantiation is excessively deep and possibly infinite.
-longObjectInstantiationChain1.ts(68,1): error TS2589: Type instantiation is excessively deep and possibly infinite.
 longObjectInstantiationChain1.ts(70,5): error TS2339: Property 'p38' does not exist on type 'merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<{ p1: number; }, { p2: number; }>, { p3: number; }>, { p4: number; }>, { p5: number; }>, { p6: number; }>, { p7: number; }>, { p8: number; }>, { p9: number; }>, { p10: number; }>, { p11: number; }>, { p12: number; }>, { p13: number; }>, { p14: number; }>, { p15: number; }>, { p16: number; }>, { p17: number; }>, { p18: number; }>, { p19: number; }>, { p20: number; }>, { p21: number; }>, { p22: number; }>, { p23: number; }>, { p24: number; }>, { p25: number; }>, { p26: number; }>, { p27: number; }>, { p28: number; }>, { p29: number; }>, { p30: number; }>, { p31: number; }>'.
 longObjectInstantiationChain1.ts(71,5): error TS2339: Property 'p51' does not exist on type 'merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<{ p1: number; }, { p2: number; }>, { p3: number; }>, { p4: number; }>, { p5: number; }>, { p6: number; }>, { p7: number; }>, { p8: number; }>, { p9: number; }>, { p10: number; }>, { p11: number; }>, { p12: number; }>, { p13: number; }>, { p14: number; }>, { p15: number; }>, { p16: number; }>, { p17: number; }>, { p18: number; }>, { p19: number; }>, { p20: number; }>, { p21: number; }>, { p22: number; }>, { p23: number; }>, { p24: number; }>, { p25: number; }>, { p26: number; }>, { p27: number; }>, { p28: number; }>, { p29: number; }>, { p30: number; }>, { p31: number; }>'.
-longObjectInstantiationChain1.ts(73,1): error TS2589: Type instantiation is excessively deep and possibly infinite.
-longObjectInstantiationChain1.ts(74,1): error TS2589: Type instantiation is excessively deep and possibly infinite.
-longObjectInstantiationChain1.ts(75,1): error TS2589: Type instantiation is excessively deep and possibly infinite.
 
 
-==== longObjectInstantiationChain1.ts (10 errors) ====
+==== longObjectInstantiationChain1.ts (4 errors) ====
     export type merge<base, props> = Omit<base, keyof props & keyof base> & props;
 
     declare const merge: <l, r>(l: l, r: r) => merge<l, r>;
@@ -79,16 +73,10 @@ longObjectInstantiationChain1.ts(75,1): error TS2589: Type instantiation is exce
 !!! error TS2339: Property 'p4' does not exist on type 'merge<merge<{ p1: number; }, { p2: number; }>, { p3: number; }>'.
 
     o25.p1;
-    ~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     o25.p10;
-    ~~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     o25.p26;
 
     o30.p1;
-    ~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     o30.p31;
     o30.p38; // error
         ~~~
@@ -98,13 +86,7 @@ longObjectInstantiationChain1.ts(75,1): error TS2589: Type instantiation is exce
 !!! error TS2339: Property 'p51' does not exist on type 'merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<merge<{ p1: number; }, { p2: number; }>, { p3: number; }>, { p4: number; }>, { p5: number; }>, { p6: number; }>, { p7: number; }>, { p8: number; }>, { p9: number; }>, { p10: number; }>, { p11: number; }>, { p12: number; }>, { p13: number; }>, { p14: number; }>, { p15: number; }>, { p16: number; }>, { p17: number; }>, { p18: number; }>, { p19: number; }>, { p20: number; }>, { p21: number; }>, { p22: number; }>, { p23: number; }>, { p24: number; }>, { p25: number; }>, { p26: number; }>, { p27: number; }>, { p28: number; }>, { p29: number; }>, { p30: number; }>, { p31: number; }>'.
 
     o50.p1;
-    ~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     o50.p31;
-    ~~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     o50.p38;
-    ~~~~~~~
-!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
     o50.p51;