fix(type-utils): intersection types involving readonly arrays are now handled in most cases

packages/type-utils/src/isTypeReadonly.ts

@@ -2,10 +2,10 @@ import { ESLintUtils } from '@typescript-eslint/experimental-utils';
 import {
   isObjectType,
   isUnionType,
-  isUnionOrIntersectionType,
   unionTypeParts,
   isPropertyReadonlyInType,
   isSymbolFlagSet,
+  isIntersectionType,
 } from 'tsutils';
 import * as ts from 'typescript';
 import { getTypeOfPropertyOfType } from './propertyTypes';
@@ -198,9 +198,35 @@ function isTypeReadonlyRecurser(
     return readonlyness;
   }
 
-  // all non-object, non-intersection types are readonly.
+  if (isIntersectionType(type)) {
+    // Special case for handling arrays/tuples (as readonly arrays/tuples always have mutable methods).
+    if (
+      type.types.some(t => checker.isArrayType(t) || checker.isTupleType(t))
+    ) {
+      const allReadonlyParts = type.types.every(
+        t =>
+          seenTypes.has(t) ||
+          isTypeReadonlyRecurser(checker, t, options, seenTypes) ===
+            Readonlyness.Readonly,
+      );
+      return allReadonlyParts ? Readonlyness.Readonly : Readonlyness.Mutable;
+    }
+
+    // Normal case.
+    const isReadonlyObject = isTypeReadonlyObject(
+      checker,
+      type,
+      options,
+      seenTypes,
+    );
+    if (isReadonlyObject !== Readonlyness.UnknownType) {
+      return isReadonlyObject;
+    }
+  }
+
+  // all non-object are readonly.
   // this should only be primitive types
-  if (!isObjectType(type) && !isUnionOrIntersectionType(type)) {
+  if (!isObjectType(type)) {
     return Readonlyness.Readonly;
   }
 

packages/type-utils/tests/isTypeReadonly.test.ts

@@ -0,0 +1,182 @@
+import * as ts from 'typescript';
+import { TSESTree } from '@typescript-eslint/experimental-utils';
+import { parseForESLint } from '@typescript-eslint/parser';
+import {
+  isTypeReadonly,
+  type ReadonlynessOptions,
+} from '../src/isTypeReadonly';
+import path from 'path';
+
+describe('isTypeReadonly', () => {
+  const rootDir = path.join(__dirname, 'fixtures');
+
+  describe('TSTypeAliasDeclaration ', () => {
+    function getType(code: string): {
+      type: ts.Type;
+      checker: ts.TypeChecker;
+    } {
+      const { ast, services } = parseForESLint(code, {
+        project: './tsconfig.json',
+        filePath: path.join(rootDir, 'file.ts'),
+        tsconfigRootDir: rootDir,
+      });
+      const checker = services.program.getTypeChecker();
+      const esTreeNodeToTSNodeMap = services.esTreeNodeToTSNodeMap;
+
+      const declaration = ast.body[0] as TSESTree.TSTypeAliasDeclaration;
+      return {
+        type: checker.getTypeAtLocation(
+          esTreeNodeToTSNodeMap.get(declaration.id),
+        ),
+        checker,
+      };
+    }
+
+    function runTestForAliasDeclaration(
+      code: string,
+      options: ReadonlynessOptions | undefined,
+      expected: boolean,
+    ): void {
+      const { type, checker } = getType(code);
+
+      const result = isTypeReadonly(checker, type, options);
+      expect(result).toBe(expected);
+    }
+
+    describe('default options', () => {
+      const options = undefined;
+
+      function runTestIsReadonly(code: string): void {
+        runTestForAliasDeclaration(code, options, true);
+      }
+
+      function runTestIsNotReadonly(code: string): void {
+        runTestForAliasDeclaration(code, options, false);
+      }
+
+      describe('basics', () => {
+        describe('is readonly', () => {
+          const runTests = runTestIsReadonly;
+
+          // Record.
+          it.each([
+            ['type Test = { readonly bar: string; };'],
+            ['type Test = Readonly<{ bar: string; }>;'],
+          ])('handles fully readonly records', runTests);
+
+          // Array.
+          it.each([
+            ['type Test = Readonly<readonly string[]>;'],
+            ['type Test = Readonly<ReadonlyArray<string>>;'],
+          ])('handles fully readonly arrays', runTests);
+
+          // Array - special case.
+          // Note: Methods are mutable but arrays are treated special; hence no failure.
+          it.each([
+            ['type Test = readonly string[];'],
+            ['type Test = ReadonlyArray<string>;'],
+          ])('treats readonly arrays as fully readonly', runTests);
+
+          // Set and Map.
+          it.each([
+            ['type Test = Readonly<ReadonlySet<string>>;'],
+            ['type Test = Readonly<ReadonlyMap<string, string>>;'],
+          ])('handles fully readonly sets and maps', runTests);
+        });
+
+        describe('is not readonly', () => {
+          const runTests = runTestIsNotReadonly;
+
+          // Record.
+          it.each([
+            ['type Test = { foo: string; };'],
+            ['type Test = { foo: string; readonly bar: number; };'],
+          ])('handles non fully readonly records', runTests);
+
+          // Array.
+          it.each([['type Test = string[]'], ['type Test = Array<string>']])(
+            'handles non fully readonly arrays',
+            runTests,
+          );
+
+          // Set and Map.
+          // Note: Methods are mutable for ReadonlySet and ReadonlyMet; hence failure.
+          it.each([
+            ['type Test = Set<string>;'],
+            ['type Test = Map<string, string>;'],
+            ['type Test = ReadonlySet<string>;'],
+            ['type Test = ReadonlyMap<string, string>;'],
+          ])('handles non fully readonly sets and maps', runTests);
+        });
+      });
+
+      describe('Intersection', () => {
+        describe('is readonly', () => {
+          const runTests = runTestIsReadonly;
+
+          it.each([
+            [
+              'type Test = Readonly<{ foo: string; bar: number; }> & Readonly<{ bar: number; }>;',
+            ],
+          ])('handles an intersection of 2 fully readonly types', runTests);
+
+          it.each([
+            [
+              'type Test = Readonly<{ foo: string; bar: number; }> & { foo: string; };',
+            ],
+          ])(
+            'handles an intersection of a fully readonly type with a mutable subtype',
+            runTests,
+          );
+
+          // Array - special case.
+          // Note: Methods are mutable but arrays are treated special; hence no failure.
+          it.each([
+            ['type Test = ReadonlyArray<string> & Readonly<{ foo: string; }>;'],
+            [
+              'type Test = readonly [string, number] & Readonly<{ foo: string; }>;',
+            ],
+          ])('handles an intersections involving a readonly array', runTests);
+        });
+
+        describe('is not readonly', () => {
+          const runTests = runTestIsNotReadonly;
+
+          it.each([
+            ['type Test = { foo: string; bar: number; } & { bar: number; };'],
+            [
+              'type Test = { foo: string; bar: number; } & Readonly<{ bar: number; }>;',
+            ],
+            [
+              'type Test = Readonly<{ bar: number; }> & { foo: string; bar: number; };',
+            ],
+          ])('handles an intersection of non fully readonly types', runTests);
+        });
+      });
+    });
+
+    describe('treatMethodsAsReadonly', () => {
+      const options: ReadonlynessOptions = {
+        treatMethodsAsReadonly: true,
+      };
+
+      function runTestIsReadonly(code: string): void {
+        runTestForAliasDeclaration(code, options, true);
+      }
+
+      // function runTestIsNotReadonly(code: string): void {
+      //   runTestForAliasDeclaration(code, options, false);
+      // }
+
+      describe('is readonly', () => {
+        const runTests = runTestIsReadonly;
+
+        // Set and Map.
+        it.each([
+          ['type Test = ReadonlySet<string>;'],
+          ['type Test = ReadonlyMap<string, string>;'],
+        ])('handles non fully readonly sets and maps', runTests);
+      });
+    });
+  });
+});