From 6e079eb35cfec79ba9965627477117f026d161ac Mon Sep 17 00:00:00 2001
From: SHIMA RYUHEI <65934663+islandryu@users.noreply.github.com>
Date: Sun, 27 Nov 2022 05:36:06 +0900
Subject: [PATCH] fix(eslint-plugin): [prefer-readonly] report if a member's
 property is reassigned (#6043)

* fix(eslint-plugin): [prefer-readonly] report if a member's property is reassigned

* format

* Add test case

* fix test case

* fix test case

Co-authored-by: Josh Goldberg <git@joshuakgoldberg.com>
---
 .../src/rules/prefer-readonly.ts              |   5 +-
 .../tests/rules/prefer-readonly.test.ts       | 345 ++++++++++++++++++
 2 files changed, 349 insertions(+), 1 deletion(-)

diff --git a/packages/eslint-plugin/src/rules/prefer-readonly.ts b/packages/eslint-plugin/src/rules/prefer-readonly.ts
index 3a1cd3f42f6..3a9e6cdca66 100644
--- a/packages/eslint-plugin/src/rules/prefer-readonly.ts
+++ b/packages/eslint-plugin/src/rules/prefer-readonly.ts
@@ -119,7 +119,10 @@ export default util.createRule<Options, MessageIds>({
             ts.isArrayLiteralExpression(parent.parent))
         ) {
           current = parent;
-        } else if (ts.isBinaryExpression(parent)) {
+        } else if (
+          ts.isBinaryExpression(parent) &&
+          !ts.isPropertyAccessExpression(current)
+        ) {
           return (
             parent.left === current &&
             parent.operatorToken.kind === ts.SyntaxKind.EqualsToken
diff --git a/packages/eslint-plugin/tests/rules/prefer-readonly.test.ts b/packages/eslint-plugin/tests/rules/prefer-readonly.test.ts
index 333ffc9b5ff..10f2e3d1e07 100644
--- a/packages/eslint-plugin/tests/rules/prefer-readonly.test.ts
+++ b/packages/eslint-plugin/tests/rules/prefer-readonly.test.ts
@@ -339,6 +339,34 @@ class Foo {
 }
       `,
     },
+    {
+      code: `
+        class Test {
+          private testObj = {
+            prop: '',
+          };
+
+          public test(): void {
+            this.testObj = '';
+          }
+        }
+      `,
+    },
+    {
+      code: `
+        class TestObject {
+          public prop: number;
+        }
+
+        class Test {
+          private testObj = new TestObject();
+
+          public test(): void {
+            this.testObj = new TestObject();
+          }
+        }
+      `,
+    },
   ],
   invalid: [
     {
@@ -742,5 +770,322 @@ function ClassWithName<TBase extends new (...args: any[]) => {}>(Base: TBase) {
         },
       ],
     },
+    {
+      code: `
+        class Test {
+          private testObj = {
+            prop: '',
+          };
+
+          public test(): void {
+            this.testObj.prop = '';
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {
+            prop: '',
+          };
+
+          public test(): void {
+            this.testObj.prop = '';
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class TestObject {
+          public prop: number;
+        }
+
+        class Test {
+          private testObj = new TestObject();
+
+          public test(): void {
+            this.testObj.prop = 10;
+          }
+        }
+      `,
+      output: `
+        class TestObject {
+          public prop: number;
+        }
+
+        class Test {
+          private readonly testObj = new TestObject();
+
+          public test(): void {
+            this.testObj.prop = 10;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 7,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {
+            prop: '',
+          };
+          public test(): void {
+            this.testObj.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {
+            prop: '',
+          };
+          public test(): void {
+            this.testObj.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj?.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj?.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj!.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj!.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj.prop.prop = '';
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj.prop.prop = '';
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj.prop.doesSomething();
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj.prop.doesSomething();
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj?.prop.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj?.prop.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj?.prop?.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj?.prop?.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj.prop?.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj.prop?.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
+    {
+      code: `
+        class Test {
+          private testObj = {};
+          public test(): void {
+            this.testObj!.prop?.prop;
+          }
+        }
+      `,
+      output: `
+        class Test {
+          private readonly testObj = {};
+          public test(): void {
+            this.testObj!.prop?.prop;
+          }
+        }
+      `,
+      errors: [
+        {
+          data: {
+            name: 'testObj',
+          },
+          line: 3,
+          messageId: 'preferReadonly',
+        },
+      ],
+    },
   ],
 });