Check if types are identical in strict assertions - fixes #43

Author: SamVerschueren

libraries/typescript/lib/typescript.d.ts

@@ -1,14 +1,14 @@
 /*! *****************************************************************************
-Copyright (c) Microsoft Corporation. All rights reserved. 
+Copyright (c) Microsoft Corporation. All rights reserved.
 Licensed under the Apache License, Version 2.0 (the "License"); you may not use
 this file except in compliance with the License. You may obtain a copy of the
-License at http://www.apache.org/licenses/LICENSE-2.0  
- 
+License at http://www.apache.org/licenses/LICENSE-2.0
+
 THIS CODE IS PROVIDED ON AN *AS IS* BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 KIND, EITHER EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED
-WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE, 
-MERCHANTABLITY OR NON-INFRINGEMENT. 
- 
+WARRANTIES OR CONDITIONS OF TITLE, FITNESS FOR A PARTICULAR PURPOSE,
+MERCHANTABLITY OR NON-INFRINGEMENT.
+
 See the Apache Version 2.0 License for specific language governing permissions
 and limitations under the License.
 ***************************************************************************** */
@@ -1995,6 +1995,19 @@ declare namespace ts {
         getAugmentedPropertiesOfType(type: Type): Symbol[];
         getRootSymbols(symbol: Symbol): ReadonlyArray<Symbol>;
         getContextualType(node: Expression): Type | undefined;
+        /**
+		 * 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;
         /**
          * Checks if type `a` is assignable to type `b`.
          */
@@ -5803,4 +5816,4 @@ declare namespace ts {
     function transform<T extends Node>(source: T | T[], transformers: TransformerFactory<T>[], compilerOptions?: CompilerOptions): TransformationResult<T>;
 }
 
-export = ts;
+export = ts;

libraries/typescript/lib/typescript.js

@@ -32344,6 +32344,7 @@ var ts;
                 var parsed = ts.getParseTreeNode(node, ts.isFunctionLike);
                 return parsed ? isImplementationOfOverload(parsed) : undefined;
 			},
+            isIdenticalTo: isTypeIdenticalTo,
             isAssignableTo: isTypeAssignableTo,
             getImmediateAliasedSymbol: getImmediateAliasedSymbol,
             getAliasedSymbol: resolveAlias,

readme.md

@@ -142,7 +142,7 @@ These options will be overridden if a `tsconfig.json` file is found in your proj
 
 ### expectType<T>(value)
 
-Check if a value is of a specific type.
+Check that `value` is identical to type `T`.
 
 ### expectError(function)
 

source/lib/assertions/assert.ts

@@ -1,7 +1,7 @@
 /**
- * Assert the type of the value.
+ * Check that `value` is identical to type `T`.
  *
- * @param value - Value that should be type checked.
+ * @param value - Value that should be identical to type `T`.
  */
 // @ts-ignore
 export const expectType = <T>(value: T) => {		// tslint:disable-line:no-unused

source/lib/assertions/handlers/strict-assertion.ts

@@ -31,12 +31,18 @@ export const strictAssertion = (checker: TypeChecker, nodes: Set<CallExpression>
 			continue;
 		}
 
-		if (!checker.isAssignableTo(expectedType, argumentType)) { // tslint:disable-line:early-exit
+		if (!checker.isAssignableTo(expectedType, argumentType)) {
 			/**
 			 * The expected type is not assignable to the argument type, but the argument type is
 			 * assignable to the expected type. This means our type is too wide.
 			 */
 			diagnostics.push(makeDiagnostic(node, `Parameter type \`${checker.typeToString(expectedType)}\` is declared too wide for argument type \`${checker.typeToString(argumentType)}\`.`));
+		} else if (!checker.isIdenticalTo(expectedType, argumentType)) {
+			/**
+			 * The expected type and argument type are assignable in both directions. We still have to check
+			 * if the types are identical. See https://github.com/Microsoft/TypeScript/blob/master/doc/spec.md#3.11.2.
+			 */
+			diagnostics.push(makeDiagnostic(node, `Parameter type \`${checker.typeToString(expectedType)}\` is not identical to argument type \`${checker.typeToString(argumentType)}\`.`));
 		}
 	}
 

source/test/fixtures/strict-types/loose/index.test-d.ts

@@ -28,3 +28,9 @@ abstract class Foo<T> {
 expectType<Foo<string | Foo<string | number>> | Foo<Date> | Foo<Symbol>>(
 	one<Foo<Date> | Foo<Symbol> | Foo<Foo<number> | string>>()
 );
+
+expectType<string | number>(one<any>());
+
+expectType<Observable<string | number> | Observable<string | number | boolean> | Observable<any>>(
+	one<Observable<string | number> | Observable<string | number | boolean> | Observable<string>>()
+);

source/test/test.ts

@@ -237,7 +237,9 @@ test('loose types', async t => {
 		[14, 0, 'error', 'Parameter type `Promise<string | number>` is declared too wide for argument type `Promise<number>`.'],
 		[16, 0, 'error', 'Parameter type `Observable<string | number>` is declared too wide for argument type `Observable<string>`.'],
 		[20, 0, 'error', 'Parameter type `Observable<string | number> | Observable<string | number | boolean>` is declared too wide for argument type `Observable<string | number> | Observable<string>`.'],
-		[28, 0, 'error', 'Parameter type `Foo<string | Foo<string | number>> | Foo<Date> | Foo<Symbol>` is declared too wide for argument type `Foo<Date> | Foo<Symbol> | Foo<string | Foo<number>>`.']
+		[28, 0, 'error', 'Parameter type `Foo<string | Foo<string | number>> | Foo<Date> | Foo<Symbol>` is declared too wide for argument type `Foo<Date> | Foo<Symbol> | Foo<string | Foo<number>>`.'],
+		[32, 0, 'error', 'Parameter type `string | number` is not identical to argument type `any`.'],
+		[34, 0, 'error', 'Parameter type `Observable<string | number> | Observable<any> | Observable<string | number | boolean>` is not identical to argument type `Observable<string | number> | Observable<string> | Observable<string | number | boolean>`.']
 	]);
 });