Add type relationship functions to checker api

Author: weswigham

src/compiler/checker.ts

@@ -103,7 +103,39 @@ namespace ts {
 
             getJsxElementAttributesType,
             getJsxIntrinsicTagNames,
-            isOptionalParameter
+            isOptionalParameter,
+
+            isIdenticalTo: (a, b) => checkTypeRelatedTo(a, b, identityRelation, /*errorNode*/undefined),
+            isSubtypeOf: (a, b) => checkTypeRelatedTo(a, b, subtypeRelation, /*errorNode*/undefined),
+            isAssignableTo: (a, b) => checkTypeRelatedTo(a, b, assignableRelation, /*errorNode*/undefined),
+            isComparableTo: areTypesComparable,
+            isInstantiationOf: (a, b) => {
+                return a && b && (a.target === b);
+            },
+
+            lookupGlobalType: name => {
+                const symbol = getGlobalTypeSymbol(name);
+                return symbol ? getDeclaredTypeOfSymbol(symbol) : unknownType;
+            },
+            lookupTypeAt: (name, node) => {
+                const symbol = resolveName(node, name, SymbolFlags.Type, /*nameNotFoundMessage*/undefined, /*nameArg*/undefined);
+                return symbol ? getDeclaredTypeOfSymbol(symbol) : unknownType;
+            },
+
+            getAnyType: () => anyType,
+            getStringType: () => stringType,
+            getNumberType: () => numberType,
+            getBooleanType: () => booleanType,
+            getVoidType: () => voidType,
+            getUndefinedType: () => undefinedType,
+            getNullType: () => nullType,
+            getESSymbolType: () => esSymbolType,
+            getNeverType: () => neverType,
+            getUnknownType: () => unknownType,
+            getStringLiteralType: (text: string) => getLiteralTypeForText(TypeFlags.StringLiteral, text),
+            getNumberLiteralType: (text: string) => getLiteralTypeForText(TypeFlags.NumberLiteral, text),
+            getFalseType: () => falseType,
+            getTrueType: () => falseType,
         };
 
         const tupleTypes: Map<TupleType> = {};

src/compiler/types.ts

@@ -1862,6 +1862,86 @@ namespace ts {
         getJsxIntrinsicTagNames(): Symbol[];
         isOptionalParameter(node: ParameterDeclaration): boolean;
 
+        /**
+         * Two types are considered identical when
+         *  - they are both the `any` type,
+         *  - they are the same primitive type,
+         *  - they are the same type parameter,
+         *  - they are union types with identical sets of constituent types, or
+         *  - they are intersection types with identical sets of constituent types, or
+         *  - they are object types with identical sets of members.
+         *
+         * This relationship is bidirectional.
+         * See [here](https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#3.11.2) for more information.
+         */
+        isIdenticalTo(a: Type, b: Type): boolean;
+        /**
+         * `a` is a ___subtype___ of `b` (and `b` is a ___supertype___ of `a`) if `a` has no excess properties with respect to `b`,
+         *  and one of the following is true:
+         *  - `a` and `b` are identical types.
+         *  - `b` is the `any` type.
+         *  - `a` is the `undefined` type.
+         *  - `a` is the `null` type and `b` is _not_ the `undefined` type.
+         *  - `a` is an enum type and `b` is the primitive type `number`.
+         *  - `a` is a string literal type and `b` is the primitive type `string`.
+         *  - `a` is a union type and each constituient type of `b` is a subtype of `b`.
+         *  - `a` is an intersection type and at least one constituent type of `a` is a subtype of `b`.
+         *  - `b` is a union type and `a` is a subtype of at least one constituent type of `b`.
+         *  - `b` is an intersection type and `a` is a subtype of each constituent type of `b`.
+         *  - `a` is a type parameter and the constraint of `a` is a subtype of `b`.
+         *  - `a` has a subset of the structural members of `b`.
+         *
+         * This relationship is directional.
+         * See [here](https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#3.11.3) for more information.
+         */
+        isSubtypeOf(a: Type, b: Type): boolean;
+        /**
+         * The assignable relationship differs only from the subtype relationship in that:
+         *  - the `any` type is assignable to, but not a subtype of, all types
+         *  - the primitive type `number` is assignable to, but not a subtype of, all enum types, and
+         *  - an object type without a particular property is assignable to an object type in which that property is optional.
+         *
+         * This relationship is directional.
+         * See [here](https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#3.11.4) for more information.
+         */
+        isAssignableTo(a: Type, b: Type): boolean;
+        /**
+         * True if `a` is assignable to `b`, or `b` is assignable to `a`. Additionally, all unions with
+         * overlapping constituient types are comparable, and unit types in the same domain are comparable.
+         * This relationship is bidirectional.
+         */
+        isComparableTo(a: Type, b: Type): boolean;
+        /**
+         * Not a formal relationship - returns true if a is an instantiation of the generic type b
+         */
+        isInstantiationOf(a: GenericType, b: GenericType): boolean;
+
+        /**
+         * Returns the declared type of the globally named symbol with meaning SymbolFlags.Type
+         *  Returns the unknown type on failure.
+         */
+        lookupGlobalType(name: string): Type;
+        /**
+         * Returns the declared type of the named symbol lexically at the position specified with meaning SymbolFlags.Type
+         *  Returns the unknown type on failure.
+         */
+        lookupTypeAt(name: string, position: Node): Type;
+
+        getAnyType(): Type;
+        getStringType(): Type;
+        getNumberType(): Type;
+        getBooleanType(): Type;
+        getVoidType(): Type;
+        getUndefinedType(): Type;
+        getNullType(): Type;
+        getESSymbolType(): Type;
+        getNeverType(): Type;
+        getUnknownType(): Type;
+        getStringLiteralType(text: string): LiteralType;
+        getNumberLiteralType(text: string): LiteralType;
+        getFalseType(): Type;
+        getTrueType(): Type;
+
         // Should not be called directly.  Should only be accessed through the Program instance.
         /* @internal */ getDiagnostics(sourceFile?: SourceFile, cancellationToken?: CancellationToken): Diagnostic[];
         /* @internal */ getGlobalDiagnostics(): Diagnostic[];