Detect unused class component method

Author: Paweł Nowak

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

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+# Prevent declaring unused methods of component class (react/no-unused-prop-types)
+
+Warns you if you have defined a method 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 {
+  action() {}
+  componentDidMount() {
+    this.action();
+  }
+  render() {
+    return null;
+  }
+}
+});
+```

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

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+/**
+ * @fileoverview Prevent declaring unused methods of component class
+ * @author Paweł Nowak
+ */
+
+'use strict';
+
+const Components = require('../util/Components');
+const astUtil = require('../util/ast');
+const docsUrl = require('../util/docsUrl');
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+const internalMethods = [
+  'constructor',
+  'componentDidCatch',
+  'componentDidMount',
+  'componentDidUpdate',
+  'componentWillMount',
+  'componentWillReceiveProps',
+  'componentWillUnmount',
+  'componentWillUpdate',
+  'getSnapshotBeforeUpdate',
+  'render',
+  'shouldComponentUpdate',
+  'UNSAFE_componentWillMount',
+  'UNSAFE_componentWillReceiveProps',
+  'UNSAFE_componentWillUpdate',
+]
+
+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) => {
+    const isNotComponent = node => (
+      !utils.isES5Component(node) &&
+      !utils.isES6Component(node) &&
+      !utils.isCreateElement(node)
+    );
+    const filterAllMethods = node => {
+      const isMethod = node.type === 'MethodDefinition';
+      const isArrowFunction = (
+        node.type === 'ClassProperty' &&
+        node.value.type === 'ArrowFunctionExpression'
+      );
+      return isMethod || isArrowFunction;
+    };
+    const checkMethods = node => {
+      if (isNotComponent(node)) return;
+      const properties = astUtil.getComponentProperties(node);
+      let methods = properties
+        .filter(property => (
+          filterAllMethods(property) &&
+          !internalMethods.includes(astUtil.getPropertyName(property))
+        ));
+      const getThisExpressions = subnode => {
+        if (!methods.length) return;
+
+        switch(subnode.type) {
+          case 'ClassProperty':
+          case 'JSXAttribute':
+          case 'MethodDefinition':
+            getThisExpressions(subnode.value);
+            break;
+          case 'ArrowFunctionExpression':
+          case 'FunctionExpression':
+            getThisExpressions(subnode.body);
+            break;
+          case 'BlockStatement':
+            subnode.body.forEach(getThisExpressions);
+            break;
+          case 'ReturnStatement':
+            getThisExpressions(subnode.argument);
+            break;
+          case 'JSXElement':
+            getThisExpressions(subnode.openingElement);
+            subnode.children.forEach(getThisExpressions);
+            break;
+          case 'JSXOpeningElement':
+            subnode.attributes.forEach(getThisExpressions);
+            break;
+          case 'JSXExpressionContainer':
+          case 'ExpressionStatement':
+            getThisExpressions(subnode.expression);
+            break;
+          case 'CallExpression':
+            getThisExpressions(subnode.callee);
+            break;
+          case 'VariableDeclaration':
+            subnode.declarations.forEach(getThisExpressions);
+            break;
+          case 'VariableDeclarator':
+            getThisExpressions(subnode.init);
+            break;
+          case 'MemberExpression':
+            if (subnode.object.type !== 'ThisExpression') return;
+
+            methods = methods.filter(method =>
+              subnode.property.name !== astUtil.getPropertyName(method)
+            );
+            break;
+          default:
+            break;
+        }
+      };
+
+      properties.forEach(getThisExpressions);
+
+      if (!methods.length) return;
+
+      methods.forEach(method => {
+        context.report({
+          node: method,
+          message: 'Unused method "{{method}}" of class "{{class}}"',
+          data: {
+            class: node.id.name,
+            method: astUtil.getPropertyName(method),
+          }
+        });
+      })
+    }
+
+    return {
+      ClassDeclaration: checkMethods,
+      ClassExpression: checkMethods,
+      ObjectExpression: checkMethods,
+    };
+  })
+};