Make expectType assertion strict

Author: SamVerschueren

libraries/typescript/lib/typescript.d.ts

@@ -1995,6 +1995,10 @@ declare namespace ts {
         getAugmentedPropertiesOfType(type: Type): Symbol[];
         getRootSymbols(symbol: Symbol): ReadonlyArray<Symbol>;
         getContextualType(node: Expression): Type | undefined;
+        /**
+         * Checks if type `a` is assignable to type `b`.
+         */
+        isAssignableTo(a: Type, b: Type): boolean;
         /**
          * returns unknownSignature in the case of an error.
          * returns undefined if the node is not valid.

libraries/typescript/lib/typescript.js

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

media/screenshot.png

@@ -27,7 +27,8 @@
 		"dist/index.js",
 		"dist/index.d.ts",
 		"dist/cli.js",
-		"dist/lib"
+		"dist/lib",
+		"libraries"
 	],
 	"keywords": [
 		"typescript",
@@ -54,6 +55,7 @@
 		"cpy-cli": "^2.0.0",
 		"del-cli": "^1.1.0",
 		"react": "^16.9.0",
+		"rxjs": "^6.5.3",
 		"tslint": "^5.11.0",
 		"tslint-xo": "^0.9.0",
 		"typescript": "^3.6.3"

media/strict-assert.png

@@ -59,7 +59,23 @@ export default concat;
 
 If we don't change the test file and we run the `tsd` command again, the test will fail.
 
-<img src="screenshot.png" width="1330">
+<img src="media/screenshot.png" width="1330">
+
+### Strict type assertions
+
+Type assertions are strict. This means that if you expect the type to be `string | number` but the argument is of type `string`, the tests will fail.
+
+```ts
+import {expectType} from 'tsd';
+import concat from '.';
+
+expectType<string>(concat('foo', 'bar'));
+expectType<string | number>(concat('foo', 'bar'));
+```
+
+If we run `tsd`, we will notice that it reports an error because the `concat` method returns the type `string` and not `string | number`.
+
+<img src="media/strict-assert.png" width="1330">
 
 ### Top-level `await`
 

package.json

@@ -2,20 +2,24 @@ import * as path from 'path';
 import {
 	flattenDiagnosticMessageText,
 	createProgram,
-	SyntaxKind,
 	Diagnostic as TSDiagnostic,
 	Program,
 	SourceFile,
 	Node,
-	forEachChild
+	forEachChild,
+	isCallExpression,
+	Identifier,
+	TypeChecker,
+	CallExpression
 } from '../../libraries/typescript';
 import {Diagnostic, DiagnosticCode, Context, Location} from './interfaces';
 
-// List of diagnostic codes that should be ignored
+// List of diagnostic codes that should be ignored in general
 const ignoredDiagnostics = new Set<number>([
 	DiagnosticCode.AwaitIsOnlyAllowedInAsyncFunction
 ]);
 
+// List of diagnostic codes which should be ignored inside `expectError` statements
 const diagnosticCodesToIgnore = new Set<DiagnosticCode>([
 	DiagnosticCode.ArgumentTypeIsNotAssignableToParameterType,
 	DiagnosticCode.PropertyDoesNotExistOnType,
@@ -27,30 +31,23 @@ const diagnosticCodesToIgnore = new Set<DiagnosticCode>([
 ]);
 
 /**
- * Extract all the `expectError` statements and convert it to a range map.
+ * Extract all assertions.
  *
- * @param program - The TypeScript program.
+ * @param program - TypeScript program.
  */
-const extractExpectErrorRanges = (program: Program) => {
-	const expectedErrors = new Map<Location, Pick<Diagnostic, 'fileName' | 'line' | 'column'>>();
+const extractAssertions = (program: Program) => {
+	const typeAssertions = new Set<CallExpression>();
+	const errorAssertions = new Set<CallExpression>();
 
 	function walkNodes(node: Node) {
-		if (node.kind === SyntaxKind.ExpressionStatement && node.getText().startsWith('expectError')) {
-			const location = {
-				fileName: node.getSourceFile().fileName,
-				start: node.getStart(),
-				end: node.getEnd()
-			};
-
-			const pos = node
-				.getSourceFile()
-				.getLineAndCharacterOfPosition(node.getStart());
-
-			expectedErrors.set(location, {
-				fileName: location.fileName,
-				line: pos.line + 1,
-				column: pos.character
-			});
+		if (isCallExpression(node)) {
+			const text = (node.expression as Identifier).getText();
+
+			if (text === 'expectType') {
+				typeAssertions.add(node);
+			} else if (text === 'expectError') {
+				errorAssertions.add(node);
+			}
 		}
 
 		forEachChild(node, walkNodes);
@@ -60,9 +57,88 @@ const extractExpectErrorRanges = (program: Program) => {
 		walkNodes(sourceFile);
 	}
 
+	return {
+		typeAssertions,
+		errorAssertions
+	};
+};
+
+/**
+ * Loop over all the `expectError` nodes and convert them to a range map.
+ *
+ * @param nodes - Set of `expectError` nodes.
+ */
+const extractExpectErrorRanges = (nodes: Set<Node>) => {
+	const expectedErrors = new Map<Location, Pick<Diagnostic, 'fileName' | 'line' | 'column'>>();
+
+	// Iterate over the nodes and add the node range to the map
+	for (const node of nodes) {
+		const location = {
+			fileName: node.getSourceFile().fileName,
+			start: node.getStart(),
+			end: node.getEnd()
+		};
+
+		const pos = node
+			.getSourceFile()
+			.getLineAndCharacterOfPosition(node.getStart());
+
+		expectedErrors.set(location, {
+			fileName: location.fileName,
+			line: pos.line + 1,
+			column: pos.character
+		});
+	}
+
 	return expectedErrors;
 };
 
+/**
+ * Assert the expected type from `expectType` calls with the provided type in the argument.
+ * Returns a list of custom diagnostics.
+ *
+ * @param checker - The TypeScript type checker.
+ * @param nodes - The `expectType` AST nodes.
+ * @return List of custom diagnostics.
+ */
+const assertTypes = (checker: TypeChecker, nodes: Set<CallExpression>): Diagnostic[] => {
+	const diagnostics: Diagnostic[] = [];
+
+	for (const node of nodes) {
+		if (!node.typeArguments) {
+			// Skip if the node does not have generics
+			continue;
+		}
+
+		// Retrieve the type to be expected. This is the type inside the generic.
+		const expectedType = checker.getTypeFromTypeNode(node.typeArguments[0]);
+		const argumentType = checker.getTypeAtLocation(node.arguments[0]);
+
+		if (!checker.isAssignableTo(argumentType, expectedType)) {
+			// The argument type is not assignable to the expected type. TypeScript will catch this for us.
+			continue;
+		}
+
+		if (!checker.isAssignableTo(expectedType, argumentType)) { // tslint:disable-line:early-exit
+			/**
+			 * At this point, 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.
+			 */
+			const position = node.getSourceFile().getLineAndCharacterOfPosition(node.getStart());
+
+			diagnostics.push({
+				fileName: node.getSourceFile().fileName,
+				message: `Parameter type \`${checker.typeToString(expectedType)}\` is declared too wide for argument type \`${checker.typeToString(argumentType)}\`.`,
+				severity: 'error',
+				line: position.line + 1,
+				column: position.character,
+			});
+		}
+	}
+
+	return diagnostics;
+};
+
 /**
  * Check if the provided diagnostic should be ignored.
  *
@@ -112,7 +188,11 @@ export const getDiagnostics = (context: Context): Diagnostic[] => {
 		.getSemanticDiagnostics()
 		.concat(program.getSyntacticDiagnostics());
 
-	const expectedErrors = extractExpectErrorRanges(program);
+	const {typeAssertions, errorAssertions} = extractAssertions(program);
+
+	const expectedErrors = extractExpectErrorRanges(errorAssertions);
+
+	result.push(...assertTypes(program.getTypeChecker(), typeAssertions));
 
 	for (const diagnostic of diagnostics) {
 		if (!diagnostic.file || ignoreDiagnostic(diagnostic, expectedErrors)) {

readme.md

@@ -3,6 +3,6 @@ import {LiteralUnion} from '.';
 
 type Pet = LiteralUnion<'dog' | 'cat', string>;
 
-expectType<Pet>('dog');
-expectType<Pet>('cat');
-expectType<Pet>('unicorn');
+expectType<Pet>('dog' as Pet);
+expectType<Pet>('cat' as Pet);
+expectType<Pet>('unicorn' as Pet);

screenshot.png

@@ -0,0 +1,7 @@
+declare const one: {
+	(foo: string, bar: string): string;
+	(foo: number, bar: number): number;
+	<T>(): T;
+};
+
+export default one;