Predefined mapped types in lib.d.ts

src/compiler/checker.ts

@@ -4550,6 +4550,10 @@ namespace ts {
                     unknownType);
         }
 
+        function getErasedTemplateTypeFromMappedType(type: MappedType) {
+            return instantiateType(getTemplateTypeFromMappedType(type), createUnaryTypeMapper(getTypeParameterFromMappedType(type), anyType));
+        }
+
         function isGenericMappedType(type: Type) {
             if (getObjectFlags(type) & ObjectFlags.Mapped) {
                 const constraintType = getConstraintTypeFromMappedType(<MappedType>type);
@@ -7190,29 +7194,18 @@ namespace ts {
                             return result;
                         }
                     }
-                    if (isGenericMappedType(target)) {
-                        // A type [P in S]: X is related to a type [P in T]: Y if T is related to S and X is related to Y.
-                        if (isGenericMappedType(source)) {
-                            if ((result = isRelatedTo(getConstraintTypeFromMappedType(<MappedType>target), getConstraintTypeFromMappedType(<MappedType>source), reportErrors)) &&
-                                (result = isRelatedTo(getTemplateTypeFromMappedType(<MappedType>source), getTemplateTypeFromMappedType(<MappedType>target), reportErrors))) {
-                                return result;
-                            }
-                        }
-                    }
-                    else {
-                        // Even if relationship doesn't hold for unions, intersections, or generic type references,
-                        // it may hold in a structural comparison.
-                        const apparentSource = getApparentType(source);
-                        // In a check of the form X = A & B, we will have previously checked if A relates to X or B relates
-                        // to X. Failing both of those we want to check if the aggregation of A and B's members structurally
-                        // relates to X. Thus, we include intersection types on the source side here.
-                        if (apparentSource.flags & (TypeFlags.Object | TypeFlags.Intersection) && target.flags & TypeFlags.Object) {
-                            // Report structural errors only if we haven't reported any errors yet
-                            const reportStructuralErrors = reportErrors && errorInfo === saveErrorInfo && !(source.flags & TypeFlags.Primitive);
-                            if (result = objectTypeRelatedTo(apparentSource, source, target, reportStructuralErrors)) {
-                                errorInfo = saveErrorInfo;
-                                return result;
-                            }
+                    // Even if relationship doesn't hold for unions, intersections, or generic type references,
+                    // it may hold in a structural comparison.
+                    const apparentSource = getApparentType(source);
+                    // In a check of the form X = A & B, we will have previously checked if A relates to X or B relates
+                    // to X. Failing both of those we want to check if the aggregation of A and B's members structurally
+                    // relates to X. Thus, we include intersection types on the source side here.
+                    if (apparentSource.flags & (TypeFlags.Object | TypeFlags.Intersection) && target.flags & TypeFlags.Object) {
+                        // Report structural errors only if we haven't reported any errors yet
+                        const reportStructuralErrors = reportErrors && errorInfo === saveErrorInfo && !(source.flags & TypeFlags.Primitive);
+                        if (result = objectTypeRelatedTo(apparentSource, source, target, reportStructuralErrors)) {
+                            errorInfo = saveErrorInfo;
+                            return result;
                         }
                     }
                 }
@@ -7441,6 +7434,9 @@ namespace ts {
                 if (expandingFlags === 3) {
                     result = Ternary.Maybe;
                 }
+                else if (isGenericMappedType(source) || isGenericMappedType(target)) {
+                    result = mappedTypeRelatedTo(source, target, reportErrors);
+                }
                 else {
                     result = propertiesRelatedTo(source, target, reportErrors);
                     if (result) {
@@ -7472,6 +7468,30 @@ namespace ts {
                 return result;
             }
 
+            // A type [P in S]: X is related to a type [P in T]: Y if T is related to S and X is related to Y.
+            function mappedTypeRelatedTo(source: Type, target: Type, reportErrors: boolean): Ternary {
+                if (isGenericMappedType(source) && isGenericMappedType(target)) {
+                    let result: Ternary;
+                    if (relation === identityRelation) {
+                        const readonlyMatches = !(<MappedType>source).declaration.readonlyToken === !(<MappedType>target).declaration.readonlyToken;
+                        const optionalMatches = !(<MappedType>source).declaration.questionToken === !(<MappedType>target).declaration.questionToken;
+                        if (readonlyMatches && optionalMatches) {
+                            if (result = isRelatedTo(getConstraintTypeFromMappedType(<MappedType>target), getConstraintTypeFromMappedType(<MappedType>source), reportErrors)) {
+                                return result & isRelatedTo(getErasedTemplateTypeFromMappedType(<MappedType>source), getErasedTemplateTypeFromMappedType(<MappedType>target), reportErrors);
+                            }
+                        }
+                    }
+                    else {
+                        if (relation === comparableRelation || !(<MappedType>source).declaration.questionToken || (<MappedType>target).declaration.questionToken) {
+                            if (result = isRelatedTo(getConstraintTypeFromMappedType(<MappedType>target), getConstraintTypeFromMappedType(<MappedType>source), reportErrors)) {
+                                return result & isRelatedTo(getTemplateTypeFromMappedType(<MappedType>source), getTemplateTypeFromMappedType(<MappedType>target), reportErrors);
+                            }
+                        }
+                    }
+                }
+                return Ternary.False;
+            }
+
             function propertiesRelatedTo(source: Type, target: Type, reportErrors: boolean): Ternary {
                 if (relation === identityRelation) {
                     return propertiesIdenticalTo(source, target);

src/lib/es5.d.ts

@@ -180,7 +180,7 @@ interface ObjectConstructor {
       * Prevents the modification of existing property attributes and values, and prevents the addition of new properties.
       * @param o Object on which to lock the attributes.
       */
-    freeze<T>(o: T): T;
+    freeze<T>(o: T): Readonly<T>;
 
     /**
       * Prevents the addition of new properties to an object.
@@ -1343,6 +1343,34 @@ interface ArrayLike<T> {
     readonly [n: number]: T;
 }
 
+/**
+ * Make all properties in T optional
+ */
+type Partial<T> = {
+    [P in keyof T]?: T[P];
+};
+
+/**
+ * Make all properties in T readonly
+ */
+type Readonly<T> = {
+    readonly [P in keyof T]: T[P];
+};
+
+/**
+ * From T pick a set of properties K
+ */
+type Pick<T, K extends keyof T> = {
+    [P in K]: T[P];
+}
+
+/**
+ * Construct a type with a set of properties K of type T
+ */
+type Record<K extends string | number, T> = {
+    [P in K]: T;
+}
+
 /**
   * Represents a raw buffer of binary data, which is used to store data for the
   * different typed arrays. ArrayBuffers cannot be read from or written to directly,

tests/baselines/reference/mappedTypeErrors.errors.txt

@@ -1,41 +1,29 @@
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(34,20): error TS2313: Type parameter 'P' has a circular constraint.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(35,20): error TS2322: Type 'Date' is not assignable to type 'string | number'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(20,20): error TS2313: Type parameter 'P' has a circular constraint.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(21,20): error TS2322: Type 'Date' is not assignable to type 'string | number'.
   Type 'Date' is not assignable to type 'number'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(36,19): error TS2344: Type 'Date' does not satisfy the constraint 'string | number'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(22,19): error TS2344: Type 'Date' does not satisfy the constraint 'string | number'.
   Type 'Date' is not assignable to type 'number'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(39,24): error TS2344: Type '"foo"' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(40,24): error TS2344: Type '"name" | "foo"' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(25,24): error TS2344: Type '"foo"' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(26,24): error TS2344: Type '"name" | "foo"' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
   Type '"foo"' is not assignable to type '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(42,24): error TS2344: Type '"x" | "y"' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(28,24): error TS2344: Type '"x" | "y"' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
   Type '"x"' is not assignable to type '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(44,24): error TS2344: Type 'undefined' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(47,24): error TS2344: Type 'T' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(30,24): error TS2344: Type 'undefined' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(33,24): error TS2344: Type 'T' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
   Type 'T' is not assignable to type '"visible"'.
-tests/cases/conformance/types/mapped/mappedTypeErrors.ts(51,24): error TS2344: Type 'T' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(37,24): error TS2344: Type 'T' does not satisfy the constraint '"name" | "width" | "height" | "visible"'.
   Type 'string | number' is not assignable to type '"name" | "width" | "height" | "visible"'.
     Type 'string' is not assignable to type '"name" | "width" | "height" | "visible"'.
       Type 'T' is not assignable to type '"visible"'.
         Type 'string | number' is not assignable to type '"visible"'.
           Type 'string' is not assignable to type '"visible"'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(59,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]?: T[P]; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(60,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]: T[P]; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(61,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]?: T[P]; }'.
+tests/cases/conformance/types/mapped/mappedTypeErrors.ts(66,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]: T[P][]; }'.
 
 
-==== tests/cases/conformance/types/mapped/mappedTypeErrors.ts (9 errors) ====
-
-    type Partial<T> = {
-        [P in keyof T]?: T[P];
-    };
-
-    type Readonly<T> = {
-        readonly [P in keyof T]: T[P];
-    };
-
-    type Pick<T, K extends keyof T> = {
-        [P in K]: T[P];
-    }
-
-    type Record<K extends string | number, T> = {
-        [_ in K]: T;
-    }
+==== tests/cases/conformance/types/mapped/mappedTypeErrors.ts (13 errors) ====
 
     interface Shape {
         name: string;
@@ -53,6 +41,8 @@ tests/cases/conformance/types/mapped/mappedTypeErrors.ts(51,24): error TS2344: T
         y: number;
     }
 
+    // Constraint checking
+
     type T00 = { [P in P]: string };  // Error
                        ~
 !!! error TS2313: Type parameter 'P' has a circular constraint.
@@ -107,4 +97,33 @@ tests/cases/conformance/types/mapped/mappedTypeErrors.ts(51,24): error TS2344: T
 
     function f4<T extends keyof Named>(x: T) {
         let y: Pick<Shape, T>;
+    }
+
+    // Type identity checking
+
+    function f10<T>() {
+        type K = keyof T;
+        var x: { [P in keyof T]: T[P] };
+        var x: { [Q in keyof T]: T[Q] };
+        var x: { [R in K]: T[R] };
+    }
+
+    function f11<T>() {
+        var x: { [P in keyof T]: T[P] };
+        var x: { [P in keyof T]?: T[P] };  // Error
+            ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]?: T[P]; }'.
+        var x: { readonly [P in keyof T]: T[P] };  // Error
+            ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]: T[P]; }'.
+        var x: { readonly [P in keyof T]?: T[P] };  // Error
+            ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ readonly [P in keyof T]?: T[P]; }'.
+    }
+
+    function f12<T>() {
+        var x: { [P in keyof T]: T[P] };
+        var x: { [P in keyof T]: T[P][] };  // Error
+            ~
+!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'x' must be of type '{ [P in keyof T]: T[P]; }', but here has type '{ [P in keyof T]: T[P][]; }'.
     }

tests/baselines/reference/mappedTypeErrors.js

@@ -1,21 +1,5 @@
 //// [mappedTypeErrors.ts]
 
-type Partial<T> = {
-    [P in keyof T]?: T[P];
-};
-
-type Readonly<T> = {
-    readonly [P in keyof T]: T[P];
-};
-
-type Pick<T, K extends keyof T> = {
-    [P in K]: T[P];
-}
-
-type Record<K extends string | number, T> = {
-    [_ in K]: T;
-}
-
 interface Shape {
     name: string;
     width: number;
@@ -32,6 +16,8 @@ interface Point {
     y: number;
 }
 
+// Constraint checking
+
 type T00 = { [P in P]: string };  // Error
 type T01 = { [P in Date]: number };  // Error
 type T02 = Record<Date, number>;  // Error
@@ -58,6 +44,27 @@ function f3<T extends keyof Shape>(x: T) {
 
 function f4<T extends keyof Named>(x: T) {
     let y: Pick<Shape, T>;
+}
+
+// Type identity checking
+
+function f10<T>() {
+    type K = keyof T;
+    var x: { [P in keyof T]: T[P] };
+    var x: { [Q in keyof T]: T[Q] };
+    var x: { [R in K]: T[R] };
+}
+
+function f11<T>() {
+    var x: { [P in keyof T]: T[P] };
+    var x: { [P in keyof T]?: T[P] };  // Error
+    var x: { readonly [P in keyof T]: T[P] };  // Error
+    var x: { readonly [P in keyof T]?: T[P] };  // Error
+}
+
+function f12<T>() {
+    var x: { [P in keyof T]: T[P] };
+    var x: { [P in keyof T]: T[P][] };  // Error
 }
 
 //// [mappedTypeErrors.js]
@@ -73,21 +80,25 @@ function f3(x) {
 function f4(x) {
     var y;
 }
+// Type identity checking
+function f10() {
+    var x;
+    var x;
+    var x;
+}
+function f11() {
+    var x;
+    var x; // Error
+    var x; // Error
+    var x; // Error
+}
+function f12() {
+    var x;
+    var x; // Error
+}
 
 
 //// [mappedTypeErrors.d.ts]
-declare type Partial<T> = {
-    [P in keyof T]?: T[P];
-};
-declare type Readonly<T> = {
-    readonly [P in keyof T]: T[P];
-};
-declare type Pick<T, K extends keyof T> = {
-    [P in K]: T[P];
-};
-declare type Record<K extends string | number, T> = {
-    [_ in K]: T;
-};
 interface Shape {
     name: string;
     width: number;
@@ -119,3 +130,6 @@ declare function f1<T>(x: T): void;
 declare function f2<T extends string | number>(x: T): void;
 declare function f3<T extends keyof Shape>(x: T): void;
 declare function f4<T extends keyof Named>(x: T): void;
+declare function f10<T>(): void;
+declare function f11<T>(): void;
+declare function f12<T>(): void;