[New] add no-unused-class-component-methods

CHANGELOG.md

@@ -5,6 +5,11 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 
 ## Unreleased
 
+### Added
+* [`no-unused-class-component-methods`]: Handle unused class component methods ([#2166][] @jakeleventhal @pawelnvk)
+
+[#2166]: https://github.com/yannickcr/eslint-plugin-react/pull/2166
+
 ## [7.26.1] - 2021.09.29
 
 ### Fixed
@@ -3482,6 +3487,7 @@ If you're still not using React 15 you can keep the old behavior by setting the
 [`no-unknown-property`]: docs/rules/no-unknown-property.md
 [`no-unsafe`]: docs/rules/no-unsafe.md
 [`no-unstable-nested-components`]: docs/rules/no-unstable-nested-components.md
+[`no-unused-class-component-methods`]: docs/rules/no-unused-class-component-methods.md
 [`no-unused-prop-types`]: docs/rules/no-unused-prop-types.md
 [`no-unused-state`]: docs/rules/no-unused-state.md
 [`no-will-update-set-state`]: docs/rules/no-will-update-set-state.md

README.md

@@ -156,6 +156,7 @@ Enable the rules that you would like to use.
 | ✔ | 🔧 | [react/no-unknown-property](docs/rules/no-unknown-property.md) | Prevent usage of unknown DOM property |
 |  |  | [react/no-unsafe](docs/rules/no-unsafe.md) | Prevent usage of unsafe lifecycle methods |
 |  |  | [react/no-unstable-nested-components](docs/rules/no-unstable-nested-components.md) | Prevent creating unstable components inside components |
+|  |  | [react/no-unused-class-component-methods](docs/rules/no-unused-class-component-methods.md) | Prevent declaring unused methods of component class |
 |  |  | [react/no-unused-prop-types](docs/rules/no-unused-prop-types.md) | Prevent definitions of unused prop types |
 |  |  | [react/no-unused-state](docs/rules/no-unused-state.md) | Prevent definition of unused state fields |
 |  |  | [react/no-will-update-set-state](docs/rules/no-will-update-set-state.md) | Prevent usage of setState in componentWillUpdate |

docs/rules/no-unused-class-component-methods.md

@@ -0,0 +1,34 @@
+# Prevent declaring unused methods of component class (react/no-unused-class-component-methods)
+
+Warns you if you have defined a method or property but it is never being used anywhere.
+
+## Rule Details
+
+The following patterns are considered warnings:
+
+```jsx
+class Foo extends React.Component {
+  handleClick() {}
+  render() {
+    return null;
+  }
+}
+```
+
+The following patterns are **not** considered warnings:
+
+```jsx
+class Foo extends React.Component {
+  static getDerivedStateFromError(error) {
+    return { hasError: true };
+  }
+  action() {}
+  componentDidMount() {
+    this.action();
+  }
+  render() {
+    return null;
+  }
+}
+});
+```

index.js

@@ -78,6 +78,7 @@ const allRules = {
   'no-unknown-property': require('./lib/rules/no-unknown-property'),
   'no-unsafe': require('./lib/rules/no-unsafe'),
   'no-unstable-nested-components': require('./lib/rules/no-unstable-nested-components'),
+  'no-unused-class-component-methods': require('./lib/rules/no-unused-class-component-methods'),
   'no-unused-prop-types': require('./lib/rules/no-unused-prop-types'),
   'no-unused-state': require('./lib/rules/no-unused-state'),
   'no-will-update-set-state': require('./lib/rules/no-will-update-set-state'),

lib/rules/no-unused-class-component-methods.js

@@ -0,0 +1,244 @@
+/**
+ * @fileoverview Prevent declaring unused methods and properties of component class
+ * @author Paweł Nowak, Berton Zhu
+ */
+
+'use strict';
+
+const Components = require('../util/Components');
+const docsUrl = require('../util/docsUrl');
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+const LIFECYCLE_METHODS = new Set([
+  'constructor',
+  'componentDidCatch',
+  'componentDidMount',
+  'componentDidUpdate',
+  'componentWillMount',
+  'componentWillReceiveProps',
+  'componentWillUnmount',
+  'componentWillUpdate',
+  'getSnapshotBeforeUpdate',
+  'render',
+  'shouldComponentUpdate',
+  'UNSAFE_componentWillMount',
+  'UNSAFE_componentWillReceiveProps',
+  'UNSAFE_componentWillUpdate'
+]);
+
+const ES6_LIFECYCLE = new Set([
+  'state'
+]);
+
+const ES5_LIFECYCLE = new Set([
+  'getInitialState',
+  'getDefaultProps',
+  'mixins'
+]);
+
+function isKeyLiteralLike(node, property) {
+  return property.type === 'Literal'
+     || (property.type === 'TemplateLiteral' && property.expressions.length === 0)
+     || (node.computed === false && property.type === 'Identifier');
+}
+
+// Descend through all wrapping TypeCastExpressions and return the expression
+// that was cast.
+function uncast(node) {
+  while (node.type === 'TypeCastExpression') {
+    node = node.expression;
+  }
+  return node;
+}
+
+// Return the name of an identifier or the string value of a literal. Useful
+// anywhere that a literal may be used as a key (e.g., member expressions,
+// method definitions, ObjectExpression property keys).
+function getName(node) {
+  node = uncast(node);
+  const type = node.type;
+
+  if (type === 'Identifier') {
+    return node.name;
+  }
+  if (type === 'Literal') {
+    return String(node.value);
+  }
+  if (type === 'TemplateLiteral' && node.expressions.length === 0) {
+    return node.quasis[0].value.raw;
+  }
+  return null;
+}
+
+function isThisExpression(node) {
+  return uncast(node).type === 'ThisExpression';
+}
+
+function getInitialClassInfo(node, isClass) {
+  return {
+    classNode: node,
+    isClass,
+    // Set of nodes where properties were defined.
+    properties: new Set(),
+
+    // Set of names of properties that we've seen used.
+    usedProperties: new Set(),
+
+    inStatic: false
+  };
+}
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Prevent declaring unused methods of component class',
+      category: 'Best Practices',
+      recommended: false,
+      url: docsUrl('no-unused-class-component-methods')
+    },
+    schema: [
+      {
+        type: 'object',
+        additionalProperties: false
+      }
+    ]
+  },
+
+  create: Components.detect((context, components, utils) => {
+    let classInfo = null;
+
+    // Takes an ObjectExpression node and adds all named Property nodes to the
+    // current set of properties.
+    function addProperty(node) {
+      classInfo.properties.add(node);
+    }
+
+    // Adds the name of the given node as a used property if the node is an
+    // Identifier or a Literal. Other node types are ignored.
+    function addUsedProperty(node) {
+      const name = getName(node);
+      if (name) {
+        classInfo.usedProperties.add(name);
+      }
+    }
+
+    function reportUnusedProperties() {
+      // Report all unused properties.
+      for (const node of classInfo.properties) { // eslint-disable-line no-restricted-syntax
+        const name = getName(node);
+        if (
+          !classInfo.usedProperties.has(name)
+           && !LIFECYCLE_METHODS.has(name)
+           && (classInfo.isClass ? !ES6_LIFECYCLE.has(name) : !ES5_LIFECYCLE.has(name))
+        ) {
+          const className = (classInfo.classNode.id && classInfo.classNode.id.name) || '';
+
+          context.report({
+            node,
+            message: `Unused method or property "${name}"${className ? ` of class "${className}"` : ''}`
+          });
+        }
+      }
+    }
+
+    function exitMethod() {
+      if (!classInfo || !classInfo.inStatic) {
+        return;
+      }
+
+      classInfo.inStatic = false;
+    }
+
+    return {
+      ClassDeclaration(node) {
+        if (utils.isES6Component(node)) {
+          classInfo = getInitialClassInfo(node, true);
+        }
+      },
+
+      ObjectExpression(node) {
+        if (utils.isES5Component(node)) {
+          classInfo = getInitialClassInfo(node, false);
+        }
+      },
+
+      'ClassDeclaration:exit'() {
+        if (!classInfo) {
+          return;
+        }
+        reportUnusedProperties();
+        classInfo = null;
+      },
+
+      'ObjectExpression:exit'(node) {
+        if (!classInfo || classInfo.classNode !== node) {
+          return;
+        }
+        reportUnusedProperties();
+        classInfo = null;
+      },
+
+      Property(node) {
+        if (!classInfo || classInfo.classNode !== node.parent) {
+          return;
+        }
+
+        if (isKeyLiteralLike(node, node.key)) {
+          addProperty(node.key);
+        }
+      },
+
+      'ClassProperty, MethodDefinition'(node) {
+        if (!classInfo) {
+          return;
+        }
+
+        if (node.static) {
+          classInfo.inStatic = true;
+          return;
+        }
+
+        if (isKeyLiteralLike(node, node.key)) {
+          addProperty(node.key);
+        }
+      },
+
+      'ClassProperty:exit': exitMethod,
+      'MethodDefinition:exit': exitMethod,
+
+      MemberExpression(node) {
+        if (!classInfo || classInfo.inStatic) {
+          return;
+        }
+
+        if (isThisExpression(node.object) && isKeyLiteralLike(node, node.property)) {
+          if (node.parent.type === 'AssignmentExpression' && node.parent.left === node) {
+            // detect `this.property = xxx`
+            addProperty(node.property);
+          } else {
+            // detect `this.property()`, `x = this.property`, etc.
+            addUsedProperty(node.property);
+          }
+        }
+      },
+
+      VariableDeclarator(node) {
+        if (!classInfo || classInfo.inStatic) {
+          return;
+        }
+
+        // detect `{ foo, bar: baz } = this`
+        if (node.init && isThisExpression(node.init) && node.id.type === 'ObjectPattern') {
+          node.id.properties.forEach((prop) => {
+            if (prop.type === 'Property' && isKeyLiteralLike(prop, prop.key)) {
+              addUsedProperty(prop.key);
+            }
+          });
+        }
+      }
+    };
+  })
+};