Remove circularity fallback deferral in getConditionalType

src/compiler/checker.ts

@@ -391,7 +391,7 @@ namespace ts {
         const intersectionTypes = createMap<IntersectionType>();
         const literalTypes = createMap<LiteralType>();
         const indexedAccessTypes = createMap<IndexedAccessType>();
-        const conditionalTypes = createMap<Type | undefined>();
+        const conditionalTypes = createMap<Type>();
         const evolvingArrayTypes: EvolvingArrayType[] = [];
         const undefinedProperties = createMap<Symbol>() as UnderscoreEscapedMap<Symbol>;
 
@@ -10131,24 +10131,11 @@ namespace ts {
             const trueType = instantiateType(root.trueType, mapper);
             const falseType = instantiateType(root.falseType, mapper);
             const instantiationId = `${root.isDistributive ? "d" : ""}${getTypeId(checkType)}>${getTypeId(extendsType)}?${getTypeId(trueType)}:${getTypeId(falseType)}`;
-            if (conditionalTypes.has(instantiationId)) {
-                const result = conditionalTypes.get(instantiationId);
-                if (result !== undefined) {
-                    return result;
-                }
-                // Somehow the conditional type depends on itself - usually via `infer` types in the `extends` clause
-                // paired with a (potentially deferred) circularly constrained type.
-                // The conditional _must_ be deferred.
-                const deferred = getDeferredConditionalType(root, mapper, /*combinedMapper*/ undefined, checkType, extendsType, trueType, falseType);
-                conditionalTypes.set(instantiationId, deferred);
-                return deferred;
+            const result = conditionalTypes.get(instantiationId);
+            if (result) {
+                return result;
             }
-            conditionalTypes.set(instantiationId, undefined);
             const newResult = getConditionalTypeWorker(root, mapper, checkType, extendsType, trueType, falseType);
-            const cachedRecursiveResult = conditionalTypes.get(instantiationId);
-            if (cachedRecursiveResult) {
-                return cachedRecursiveResult;
-            }
             conditionalTypes.set(instantiationId, newResult);
             return newResult;
         }

tests/baselines/reference/circularTypeofWithVarOrFunc.errors.txt

@@ -4,11 +4,13 @@ tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarO
 tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(5,6): error TS2456: Type alias 'typeAlias2' circularly references itself.
 tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(7,18): error TS2577: Return type annotation circularly references itself.
 tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(9,6): error TS2456: Type alias 'typeAlias3' circularly references itself.
-tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(20,3): error TS2322: Type 'number' is not assignable to type 'ReturnType<(input: Input) => ReturnType<typeof mul>>'.
-tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(26,20): error TS2322: Type '0' is not assignable to type 'ReturnType<() => ReturnType<typeof f>>'.
+tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(18,6): error TS2456: Type alias 'R' circularly references itself.
+tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(19,29): error TS2577: Return type annotation circularly references itself.
+tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(25,6): error TS2456: Type alias 'R2' circularly references itself.
+tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts(26,15): error TS2577: Return type annotation circularly references itself.
 
 
-==== tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts (8 errors) ====
+==== tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarOrFunc.ts (10 errors) ====
     type typeAlias1 = typeof varOfAliasedType1;
          ~~~~~~~~~~
 !!! error TS2456: Type alias 'typeAlias1' circularly references itself.
@@ -39,16 +41,20 @@ tests/cases/conformance/types/specifyingTypes/typeQueries/circularTypeofWithVarO
     }
 
     type R = ReturnType<typeof mul>;
+         ~
+!!! error TS2456: Type alias 'R' circularly references itself.
     function mul(input: Input): R {
+                                ~
+!!! error TS2577: Return type annotation circularly references itself.
       return input.a * input.b;
-      ~~~~~~~~~~~~~~~~~~~~~~~~~
-!!! error TS2322: Type 'number' is not assignable to type 'ReturnType<(input: Input) => ReturnType<typeof mul>>'.
     }
 
     // Repro from #26104
 
     type R2 = ReturnType<typeof f>;
+         ~~
+!!! error TS2456: Type alias 'R2' circularly references itself.
     function f(): R2 { return 0; }
-                       ~~~~~~~~~
-!!! error TS2322: Type '0' is not assignable to type 'ReturnType<() => ReturnType<typeof f>>'.
+                  ~~
+!!! error TS2577: Return type annotation circularly references itself.
 

tests/baselines/reference/circularTypeofWithVarOrFunc.types

@@ -37,11 +37,11 @@ interface Input {
 }
 
 type R = ReturnType<typeof mul>;
->R : ReturnType<(input: Input) => ReturnType<typeof mul>>
->mul : (input: Input) => ReturnType<typeof mul>
+>R : any
+>mul : (input: Input) => any
 
 function mul(input: Input): R {
->mul : (input: Input) => ReturnType<typeof mul>
+>mul : (input: Input) => any
 >input : Input
 
   return input.a * input.b;
@@ -57,10 +57,10 @@ function mul(input: Input): R {
 // Repro from #26104
 
 type R2 = ReturnType<typeof f>;
->R2 : ReturnType<() => ReturnType<typeof f>>
->f : () => ReturnType<typeof f>
+>R2 : any
+>f : () => any
 
 function f(): R2 { return 0; }
->f : () => ReturnType<typeof f>
+>f : () => any
 >0 : 0
 

tests/baselines/reference/recursiveResolveTypeMembers.errors.txt

@@ -1,13 +1,16 @@
+tests/cases/compiler/recursiveResolveTypeMembers.ts(4,49): error TS2577: Return type annotation circularly references itself.
 tests/cases/compiler/recursiveResolveTypeMembers.ts(4,58): error TS2304: Cannot find name 'H'.
 tests/cases/compiler/recursiveResolveTypeMembers.ts(4,62): error TS2574: A rest element type must be an array type.
 tests/cases/compiler/recursiveResolveTypeMembers.ts(4,79): error TS2304: Cannot find name 'R'.
 
 
-==== tests/cases/compiler/recursiveResolveTypeMembers.ts (3 errors) ====
+==== tests/cases/compiler/recursiveResolveTypeMembers.ts (4 errors) ====
     // Repro from #25291
 
     type PromisedTuple<L extends any[], U = (...args: L) => void> =
         U extends (h: infer H, ...args: infer R) => [Promise<H>, ...PromisedTuple<R>] ? [] : []
+                                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2577: Return type annotation circularly references itself.
                                                              ~
 !!! error TS2304: Cannot find name 'H'.
                                                                  ~~~~~~~~~~~~~~~~~~~