fix(eslint-plugin): [class-methods-use-this] detect a problematic cas…

…e for private/protected members if `ignoreClassesThatImplementAnInterface` is set (#7705)

* fix(eslint-plugin): [no-shadow] fix lint error in tests

* fix(eslint-plugin): [class-methods-use-this] Add the test case for getter/setter

* fix(eslint-plugin): [class-methods-use-this] Add the test case for class private field

* fix(eslint-plugin): [class-methods-use-this] Allow to detect a problematic case for private/protected members if `ignoreClassesThatImplementAnInterface` is set

* Revert no-shadow.test.ts changes

---------

Co-authored-by: Josh Goldberg <git@joshuakgoldberg.com>

packages/eslint-plugin/docs/rules/class-methods-use-this.md

@@ -16,7 +16,7 @@ This rule adds the following options:
 ```ts
 interface Options extends BaseClassMethodsUseThisOptions {
   ignoreOverrideMethods?: boolean;
-  ignoreClassesThatImplementAnInterface?: boolean;
+  ignoreClassesThatImplementAnInterface?: boolean | 'public-fields';
 }
 
 const defaultOptions: Options = {
@@ -41,10 +41,16 @@ class X {
 
 ### `ignoreClassesThatImplementAnInterface`
 
-Makes the rule ignore all class members that are defined within a class that `implements` a type.
+Makes the rule ignore class members that are defined within a class that `implements` a type.
+If specified, it can be either:
+
+- `true`: Ignore all classes that implement an interface
+- `'public-fields'`: Ignore only the public fields of classes that implement an interface
 
 It's important to note that this option does not only apply to members defined in the interface as that would require type information.
 
+#### `true`
+
 Example of a correct code when `ignoreClassesThatImplementAnInterface` is set to `true`:
 
 ```ts option='{ "ignoreClassesThatImplementAnInterface": true }' showPlaygroundButton
@@ -53,3 +59,33 @@ class X implements Y {
   property = () => {};
 }
 ```
+
+#### `'public-fields'`
+
+Example of a incorrect code when `ignoreClassesThatImplementAnInterface` is set to `'public-fields'`:
+
+<!--tabs-->
+
+##### ❌ Incorrect
+
+```ts
+class X implements Y {
+  method() {}
+  property = () => {};
+
+  private privateMethod() {}
+  private privateProperty = () => {};
+
+  protected privateMethod() {}
+  protected privateProperty = () => {};
+}
+```
+
+##### ✅ Correct
+
+```ts
+class X implements Y {
+  method() {}
+  property = () => {};
+}
+```

packages/eslint-plugin/src/rules/class-methods-use-this.ts

@@ -14,7 +14,7 @@ type Options = [
     exceptMethods?: string[];
     enforceForClassFields?: boolean;
     ignoreOverrideMethods?: boolean;
-    ignoreClassesThatImplementAnInterface?: boolean;
+    ignoreClassesThatImplementAnInterface?: boolean | 'public-fields';
   },
 ];
 type MessageIds = 'missingThis';
@@ -53,7 +53,18 @@ export default createRule<Options, MessageIds>({
             description: 'Ingore members marked with the `override` modifier',
           },
           ignoreClassesThatImplementAnInterface: {
-            type: 'boolean',
+            oneOf: [
+              {
+                type: 'boolean',
+                description: 'Ignore all classes that implement an interface',
+              },
+              {
+                type: 'string',
+                enum: ['public-fields'],
+                description:
+                  'Ignore only the public fields of classes that implement an interface',
+              },
+            ],
             description:
               'Ignore classes that specifically implement some interface',
           },
@@ -146,6 +157,16 @@ export default createRule<Options, MessageIds>({
       return oldStack;
     }
 
+    function isPublicField(
+      accessibility: TSESTree.Accessibility | undefined,
+    ): boolean {
+      if (!accessibility || accessibility === 'public') {
+        return true;
+      }
+
+      return false;
+    }
+
     /**
      * Check if the node is an instance method not excluded by config
      */
@@ -189,8 +210,11 @@ export default createRule<Options, MessageIds>({
         stackContext?.member == null ||
         stackContext.usesThis ||
         (ignoreOverrideMethods && stackContext.member.override) ||
-        (ignoreClassesThatImplementAnInterface &&
-          stackContext.class.implements.length)
+        (ignoreClassesThatImplementAnInterface === true &&
+          stackContext.class.implements.length > 0) ||
+        (ignoreClassesThatImplementAnInterface === 'public-fields' &&
+          stackContext.class.implements.length > 0 &&
+          isPublicField(stackContext.member.accessibility))
       ) {
         return;
       }