Improve reverse mapped types

src/compiler/checker.ts

@@ -14887,10 +14887,19 @@ namespace ts {
             return type;
         }
 
+        // We consider a type to be partially inferable if it isn't marked non-inferable or if it is
+        // an object literal type with at least one property of an inferable type. For example, an object
+        // literal { a: 123, b: x => true } is marked non-inferable because it contains a context sensitive
+        // arrow function, but is considered partially inferable because property 'a' has an inferable type.
+        function isPartiallyInferableType(type: Type): boolean {
+            return !(getObjectFlags(type) & ObjectFlags.NonInferrableType) ||
+                isObjectLiteralType(type) && some(getPropertiesOfType(type), prop => isPartiallyInferableType(getTypeOfSymbol(prop)));
+        }
+
         function createReverseMappedType(source: Type, target: MappedType, constraint: IndexType) {
-            // If any property contains context sensitive functions that have been skipped, the source type
-            // is incomplete and we can't infer a meaningful input type.
-            if (getObjectFlags(source) & ObjectFlags.NonInferrableType || getPropertiesOfType(source).length === 0 && !getIndexInfoOfType(source, IndexKind.String)) {
+            // We consider a source type reverse mappable if it has a string index signature or if
+            // it has one or more properties and is of a partially inferable type.
+            if (!(getIndexInfoOfType(source, IndexKind.String) || getPropertiesOfType(source).length !== 0 && isPartiallyInferableType(source))) {
                 return undefined;
             }
             // For arrays and tuples we infer new arrays and tuples where the reverse mapping has been
@@ -15275,7 +15284,11 @@ namespace ts {
                         const inferredType = inferTypeForHomomorphicMappedType(source, target, <IndexType>constraintType);
                         if (inferredType) {
                             const savePriority = priority;
-                            priority |= InferencePriority.HomomorphicMappedType;
+                            // We assign a lower priority to inferences made from types containing non-inferrable
+                            // types because we may only have a partial result (i.e. we may have failed to make
+                            // reverse inferences for some properties).
+                            priority |= getObjectFlags(source) & ObjectFlags.NonInferrableType ?
+                                InferencePriority.PartialHomomorphicMappedType : InferencePriority.HomomorphicMappedType;
                             inferFromTypes(inferredType, inference.typeParameter);
                             priority = savePriority;
                         }

src/compiler/types.ts

@@ -4405,15 +4405,16 @@ namespace ts {
     export type TypeMapper = (t: TypeParameter) => Type;
 
     export const enum InferencePriority {
-        NakedTypeVariable           = 1 << 0,  // Naked type variable in union or intersection type
-        HomomorphicMappedType       = 1 << 1,  // Reverse inference for homomorphic mapped type
-        MappedTypeConstraint        = 1 << 2,  // Reverse inference for mapped type
-        ReturnType                  = 1 << 3,  // Inference made from return type of generic function
-        LiteralKeyof                = 1 << 4,  // Inference made from a string literal to a keyof T
-        NoConstraints               = 1 << 5,  // Don't infer from constraints of instantiable types
-        AlwaysStrict                = 1 << 6,  // Always use strict rules for contravariant inferences
-
-        PriorityImpliesCombination  = ReturnType | MappedTypeConstraint | LiteralKeyof,  // These priorities imply that the resulting type should be a combination of all candidates
+        NakedTypeVariable            = 1 << 0,  // Naked type variable in union or intersection type
+        HomomorphicMappedType        = 1 << 1,  // Reverse inference for homomorphic mapped type
+        PartialHomomorphicMappedType = 1 << 2,  // Partial reverse inference for homomorphic mapped type
+        MappedTypeConstraint         = 1 << 3,  // Reverse inference for mapped type
+        ReturnType                   = 1 << 4,  // Inference made from return type of generic function
+        LiteralKeyof                 = 1 << 5,  // Inference made from a string literal to a keyof T
+        NoConstraints                = 1 << 6,  // Don't infer from constraints of instantiable types
+        AlwaysStrict                 = 1 << 7,  // Always use strict rules for contravariant inferences
+
+        PriorityImpliesCombination = ReturnType | MappedTypeConstraint | LiteralKeyof,  // These priorities imply that the resulting type should be a combination of all candidates
     }
 
     /* @internal */

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2413,12 +2413,13 @@ declare namespace ts {
     enum InferencePriority {
         NakedTypeVariable = 1,
         HomomorphicMappedType = 2,
-        MappedTypeConstraint = 4,
-        ReturnType = 8,
-        LiteralKeyof = 16,
-        NoConstraints = 32,
-        AlwaysStrict = 64,
-        PriorityImpliesCombination = 28
+        PartialHomomorphicMappedType = 4,
+        MappedTypeConstraint = 8,
+        ReturnType = 16,
+        LiteralKeyof = 32,
+        NoConstraints = 64,
+        AlwaysStrict = 128,
+        PriorityImpliesCombination = 56
     }
     /** @deprecated Use FileExtensionInfo instead. */
     type JsFileExtensionInfo = FileExtensionInfo;

tests/baselines/reference/api/typescript.d.ts

@@ -2413,12 +2413,13 @@ declare namespace ts {
     enum InferencePriority {
         NakedTypeVariable = 1,
         HomomorphicMappedType = 2,
-        MappedTypeConstraint = 4,
-        ReturnType = 8,
-        LiteralKeyof = 16,
-        NoConstraints = 32,
-        AlwaysStrict = 64,
-        PriorityImpliesCombination = 28
+        PartialHomomorphicMappedType = 4,
+        MappedTypeConstraint = 8,
+        ReturnType = 16,
+        LiteralKeyof = 32,
+        NoConstraints = 64,
+        AlwaysStrict = 128,
+        PriorityImpliesCombination = 56
     }
     /** @deprecated Use FileExtensionInfo instead. */
     type JsFileExtensionInfo = FileExtensionInfo;

tests/baselines/reference/mappedTypeInferenceErrors.errors.txt

@@ -20,7 +20,7 @@ tests/cases/conformance/types/mapped/mappedTypeInferenceErrors.ts(16,9): error T
             baz: 42
             ~~~
 !!! error TS2322: Type 'number' is not assignable to type '() => unknown'.
-!!! related TS6500 tests/cases/conformance/types/mapped/mappedTypeInferenceErrors.ts:16:9: The expected type comes from property 'baz' which is declared here on type 'ComputedOf<{ bar: number; baz: unknown; }>'
+!!! related TS6500 tests/cases/conformance/types/mapped/mappedTypeInferenceErrors.ts:16:9: The expected type comes from property 'baz' which is declared here on type 'ComputedOf<{ bar: unknown; baz: unknown; }>'
         }
     });
 

tests/baselines/reference/reverseMappedPartiallyInferableTypes.errors.txt

@@ -0,0 +1,101 @@
+tests/cases/compiler/reverseMappedPartiallyInferableTypes.ts(91,20): error TS2571: Object is of type 'unknown'.
+
+
+==== tests/cases/compiler/reverseMappedPartiallyInferableTypes.ts (1 errors) ====
+    // Repro from #30505
+
+    export type Prop<T> = { (): T }
+    export type PropType<T> = Prop<T>;
+    export type PropDefaultValue<T> = T;
+
+
+    export type PropValidatorFunction<T> = (value: T) => boolean;
+    export type PropValidator<T> = PropOptions<T>;
+
+
+    export type PropOptions<T> = {
+        type: PropType<T>;
+
+        value?: PropDefaultValue<T>,
+        required?: boolean;
+        validator?: PropValidatorFunction<T>;
+    }
+
+    export type RecordPropsDefinition<T> = {
+        [K in keyof T]: PropValidator<T[K]>
+    }
+    export type PropsDefinition<T> = RecordPropsDefinition<T>;
+
+
+    declare function extend<T>({ props }: { props: PropsDefinition<T> }):  PropsDefinition<T>;
+
+    interface MyType {
+        valid: boolean;
+    }
+
+    const r = extend({
+        props: {
+            notResolved: {
+                type: Object as PropType<MyType>,
+                validator: x => {
+                    return x.valid;
+                }
+            },
+            explicit: {
+                type: Object as PropType<MyType>,
+                validator: (x: MyType) => {
+                    return x.valid;
+                }
+            }
+        }
+    })
+
+    r.explicit
+    r.notResolved
+    r.explicit.required
+    r.notResolved.required
+
+    // Modified repro from #30505
+
+    type Box<T> = {
+        contents?: T;
+        contains?(content: T): boolean;
+    };
+
+    type Mapped<T> = {
+        [K in keyof T]: Box<T[K]>;
+    }
+
+    declare function id<T>(arg: Mapped<T>): Mapped<T>;
+
+    // All properties have inferable types
+
+    const obj1 = id({
+        foo: {
+            contents: ""
+        }
+    });
+
+    // Some properties have inferable types
+
+    const obj2 = id({
+        foo: {
+            contents: "",
+            contains(k) {
+                return k.length > 0;
+            }
+        }
+    });
+
+    // No properties have inferable types
+
+    const obj3 = id({
+        foo: {
+            contains(k) {
+                return k.length > 0;
+                       ~
+!!! error TS2571: Object is of type 'unknown'.
+            }
+        }
+    });
+

tests/baselines/reference/reverseMappedPartiallyInferableTypes.js

@@ -0,0 +1,144 @@
+//// [reverseMappedPartiallyInferableTypes.ts]
+// Repro from #30505
+
+export type Prop<T> = { (): T }
+export type PropType<T> = Prop<T>;
+export type PropDefaultValue<T> = T;
+
+
+export type PropValidatorFunction<T> = (value: T) => boolean;
+export type PropValidator<T> = PropOptions<T>;
+
+
+export type PropOptions<T> = {
+    type: PropType<T>;
+
+    value?: PropDefaultValue<T>,
+    required?: boolean;
+    validator?: PropValidatorFunction<T>;
+}
+
+export type RecordPropsDefinition<T> = {
+    [K in keyof T]: PropValidator<T[K]>
+}
+export type PropsDefinition<T> = RecordPropsDefinition<T>;
+
+
+declare function extend<T>({ props }: { props: PropsDefinition<T> }):  PropsDefinition<T>;
+
+interface MyType {
+    valid: boolean;
+}
+
+const r = extend({
+    props: {
+        notResolved: {
+            type: Object as PropType<MyType>,
+            validator: x => {
+                return x.valid;
+            }
+        },
+        explicit: {
+            type: Object as PropType<MyType>,
+            validator: (x: MyType) => {
+                return x.valid;
+            }
+        }
+    }
+})
+
+r.explicit
+r.notResolved
+r.explicit.required
+r.notResolved.required
+
+// Modified repro from #30505
+
+type Box<T> = {
+    contents?: T;
+    contains?(content: T): boolean;
+};
+
+type Mapped<T> = {
+    [K in keyof T]: Box<T[K]>;
+}
+
+declare function id<T>(arg: Mapped<T>): Mapped<T>;
+
+// All properties have inferable types
+
+const obj1 = id({
+    foo: {
+        contents: ""
+    }
+});
+
+// Some properties have inferable types
+
+const obj2 = id({
+    foo: {
+        contents: "",
+        contains(k) {
+            return k.length > 0;
+        }
+    }
+});
+
+// No properties have inferable types
+
+const obj3 = id({
+    foo: {
+        contains(k) {
+            return k.length > 0;
+        }
+    }
+});
+
+
+//// [reverseMappedPartiallyInferableTypes.js]
+"use strict";
+// Repro from #30505
+exports.__esModule = true;
+var r = extend({
+    props: {
+        notResolved: {
+            type: Object,
+            validator: function (x) {
+                return x.valid;
+            }
+        },
+        explicit: {
+            type: Object,
+            validator: function (x) {
+                return x.valid;
+            }
+        }
+    }
+});
+r.explicit;
+r.notResolved;
+r.explicit.required;
+r.notResolved.required;
+// All properties have inferable types
+var obj1 = id({
+    foo: {
+        contents: ""
+    }
+});
+// Some properties have inferable types
+var obj2 = id({
+    foo: {
+        contents: "",
+        contains: function (k) {
+            return k.length > 0;
+        }
+    }
+});
+// No properties have inferable types
+var obj3 = id({
+    foo: {
+        contains: function (k) {
+            return k.length > 0;
+        }
+    }
+});