No deep equal check in memo rule

eslint-plugin-expensify/no-deep-equal-in-memo.js

@@ -0,0 +1,174 @@
+/**
+ * ESLint rule: no-deep-equal-in-memo
+ *
+ * Enforces using shallow comparisons instead of deep equality checks in React.memo
+ * comparison functions for better performance.
+ *
+ * This rule implements the PERF-5 guideline: Use shallow comparisons instead of deep comparisons.
+ */
+import _ from 'lodash';
+
+const name = 'no-deep-equal-in-memo';
+
+const meta = {
+    type: 'problem',
+    docs: {
+        description: 'Disallow deep equality checks in React.memo comparison functions. Use shallow comparisons of specific properties instead.',
+        recommended: 'error',
+    },
+    schema: [],
+    messages: {
+        noDeepEqualInMemo: 'Avoid using deep equality checks ({{functionName}}) in React.memo. Compare specific relevant properties with shallow equality instead for better performance.',
+    },
+};
+
+/**
+ * Set of deep comparison function names to detect
+ */
+const DEEP_COMPARISON_FUNCTIONS = new Set([
+    'deepEqual',
+    'isEqual',
+]);
+
+/**
+ * Check if a call expression is a deep comparison function
+ * @param {Node} node - The CallExpression node
+ * @returns {{isDeepComparison: boolean, functionName: string|null}}
+ */
+function isDeepComparisonCall(node) {
+    if (node.type !== 'CallExpression') {
+        return {isDeepComparison: false, functionName: null};
+    }
+
+    // Check for direct function calls: deepEqual(), isEqual()
+    if (node.callee.type === 'Identifier' && DEEP_COMPARISON_FUNCTIONS.has(node.callee.name)) {
+        return {isDeepComparison: true, functionName: node.callee.name};
+    }
+
+    // Check for lodash calls: _.isEqual()
+    if (
+        node.callee.type === 'MemberExpression'
+        && node.callee.object.type === 'Identifier'
+        && node.callee.object.name === '_'
+        && node.callee.property.type === 'Identifier'
+        && DEEP_COMPARISON_FUNCTIONS.has(node.callee.property.name)
+    ) {
+        return {isDeepComparison: true, functionName: `_.${node.callee.property.name}`};
+    }
+
+    return {isDeepComparison: false, functionName: null};
+}
+
+/**
+ * Check if a call expression is React.memo or memo
+ * @param {Node} node - The CallExpression node
+ * @returns {boolean}
+ */
+function isReactMemoCall(node) {
+    if (node.type !== 'CallExpression') {
+        return false;
+    }
+
+    // Check for React.memo()
+    if (
+        node.callee.type === 'MemberExpression'
+        && node.callee.object.type === 'Identifier'
+        && node.callee.object.name === 'React'
+        && node.callee.property.type === 'Identifier'
+        && node.callee.property.name === 'memo'
+    ) {
+        return true;
+    }
+
+    // Check for memo() (named import)
+    if (node.callee.type === 'Identifier' && node.callee.name === 'memo') {
+        return true;
+    }
+
+    return false;
+}
+
+/**
+ * Traverse AST to find deep comparison calls
+ * @param {Node} node - The node to traverse
+ * @param {Function} callback - Called when a deep comparison is found
+ * @param {Set<Node>} visited - Set of visited nodes to prevent cycles
+ */
+function traverseForDeepComparisons(node, callback, visited = new Set()) {
+    if (!node || !node.type || visited.has(node)) {
+        return;
+    }
+
+    visited.add(node);
+
+    // Check if this node is a deep comparison call
+    const {isDeepComparison, functionName} = isDeepComparisonCall(node);
+    if (isDeepComparison) {
+        callback(node, functionName);
+    }
+
+    // Traverse child nodes
+    for (const key of _.keys(node)) {
+        // Skip metadata and parent references to avoid cycles
+        if (key === 'parent' || key === 'type' || key === 'range' || key === 'loc') {
+            continue;
+        }
+
+        const value = node[key];
+
+        if (_.isArray(value)) {
+            for (const item of value) {
+                if (item && typeof item === 'object' && item.type) {
+                    traverseForDeepComparisons(item, callback, visited);
+                }
+            }
+        } else if (value && typeof value === 'object' && value.type) {
+            traverseForDeepComparisons(value, callback, visited);
+        }
+    }
+}
+
+function create(context) {
+    return {
+        CallExpression(node) {
+            // Check if this is a React.memo() or memo() call
+            if (!isReactMemoCall(node)) {
+                return;
+            }
+
+            // Check if there's a second argument (comparison function)
+            if (node.arguments.length < 2) {
+                return;
+            }
+
+            const comparisonFunction = node.arguments[1];
+
+            // The comparison function should be a function expression or arrow function
+            if (
+                comparisonFunction.type !== 'FunctionExpression'
+                && comparisonFunction.type !== 'ArrowFunctionExpression'
+            ) {
+                return;
+            }
+
+            // Traverse the comparison function to find deep comparison calls
+            const visited = new Set();
+            traverseForDeepComparisons(
+                comparisonFunction.body,
+                (deepComparisonNode, functionName) => {
+                    context.report({
+                        node: deepComparisonNode,
+                        messageId: 'noDeepEqualInMemo',
+                        data: {
+                            functionName,
+                        },
+                    });
+                },
+                visited,
+            );
+        },
+    };
+}
+
+export {name, meta, create};
+