Merge pull request #14492 from Microsoft/anyInferences

Set inference result to `any` instead of `{}` for .js files if generic type parameter inference found no candidates

Author: mhegazy

src/compiler/checker.ts

@@ -9184,13 +9184,14 @@ namespace ts {
             }
         }
 
-        function createInferenceContext(signature: Signature, inferUnionTypes: boolean): InferenceContext {
+        function createInferenceContext(signature: Signature, inferUnionTypes: boolean, useAnyForNoInferences: boolean): InferenceContext {
             const inferences = map(signature.typeParameters, createTypeInferencesObject);
             return {
                 signature,
                 inferUnionTypes,
                 inferences,
                 inferredTypes: new Array(signature.typeParameters.length),
+                useAnyForNoInferences
             };
         }
 
@@ -9604,7 +9605,7 @@ namespace ts {
                                 getInferenceMapper(context)));
                     }
                     else {
-                        inferredType = emptyObjectType;
+                        inferredType = context.useAnyForNoInferences ? anyType : emptyObjectType;
                     }
 
                     inferenceSucceeded = true;
@@ -13652,7 +13653,7 @@ namespace ts {
 
         // Instantiate a generic signature in the context of a non-generic signature (section 3.8.5 in TypeScript spec)
         function instantiateSignatureInContextOf(signature: Signature, contextualSignature: Signature, contextualMapper: TypeMapper): Signature {
-            const context = createInferenceContext(signature, /*inferUnionTypes*/ true);
+            const context = createInferenceContext(signature, /*inferUnionTypes*/ true, /*useAnyForNoInferences*/ false);
             forEachMatchingParameterType(contextualSignature, signature, (source, target) => {
                 // Type parameters from outer context referenced by source type are fixed by instantiation of the source type
                 inferTypesWithContext(context, instantiateType(source, contextualMapper), target);
@@ -14353,7 +14354,7 @@ namespace ts {
                     let candidate: Signature;
                     let typeArgumentsAreValid: boolean;
                     const inferenceContext = originalCandidate.typeParameters
-                        ? createInferenceContext(originalCandidate, /*inferUnionTypes*/ false)
+                        ? createInferenceContext(originalCandidate, /*inferUnionTypes*/ false, /*useAnyForNoInferences*/ isInJavaScriptFile(node))
                         : undefined;
 
                     while (true) {

src/compiler/types.ts

@@ -3235,6 +3235,7 @@ namespace ts {
         mapper?: TypeMapper;                // Type mapper for this inference context
         failedTypeParameterIndex?: number;  // Index of type parameter for which inference failed
         // It is optional because in contextual signature instantiation, nothing fails
+        useAnyForNoInferences?: boolean;    // Use any instead of {} for no inferences
     }
 
     /* @internal */