feat: ignore IIFE's in the no-loop-func rule

docs/src/rules/no-loop-func.md

@@ -32,7 +32,7 @@ In this case, each function created within the loop returns a different number a
 
 This error is raised to highlight a piece of code that may not work as you expect it to and could also indicate a misunderstanding of how the language works. Your code may run without any problems if you do not fix this error, but in some situations it could behave unexpectedly.
 
-This rule disallows any function within a loop that contains unsafe references (e.g. to modified variables from the outer scope).
+This rule disallows any function within a loop that contains unsafe references (e.g. to modified variables from the outer scope). This rule ignores IIFEs but not async or generator functions.
 
 Examples of **incorrect** code for this rule:
 
@@ -41,10 +41,6 @@ Examples of **incorrect** code for this rule:
 ```js
 /*eslint no-loop-func: "error"*/
 
-for (var i=10; i; i--) {
-    (function() { return i; })();
-}
-
 var i = 0;
 while(i < 5) {
     var a = function() { return i; };
@@ -73,6 +69,25 @@ for (let i = 0; i < 10; ++i) {
     setTimeout(() => console.log(foo));
 }
 foo = 100;
+
+var arr = [];
+
+for (var i = 0; i < 5; i++) {
+    arr.push((f => f)(() => i));
+}
+
+for (var i = 0; i < 5; i++) {
+    arr.push((() => {
+        return () => i;
+    })());
+}
+
+for (var i = 0; i < 5; i++) {
+    (function fun () {
+        if (arr.includes(fun)) return i;
+        else arr.push(fun);
+    })();
+}
 ```
 
 :::
@@ -106,6 +121,22 @@ for (let i=10; i; i--) {
     a();
 }
 //... no modifications of foo after this loop ...
+
+var arr = [];
+
+for (var i=10; i; i--) {
+    (function() { return i; })();
+}
+
+for (var i = 0; i < 5; i++) {
+    arr.push((f => f)((() => i)()));
+}
+
+for (var i = 0; i < 5; i++) {
+    arr.push((() => {
+        return (() => i)();
+    })());
+}
 ```
 
 :::

lib/rules/no-loop-func.js

@@ -9,140 +9,16 @@
 // Helpers
 //------------------------------------------------------------------------------
 
-/**
- * Gets the containing loop node of a specified node.
- *
- * We don't need to check nested functions, so this ignores those.
- * `Scope.through` contains references of nested functions.
- * @param {ASTNode} node An AST node to get.
- * @returns {ASTNode|null} The containing loop node of the specified node, or
- *      `null`.
- */
-function getContainingLoopNode(node) {
-    for (let currentNode = node; currentNode.parent; currentNode = currentNode.parent) {
-        const parent = currentNode.parent;
-
-        switch (parent.type) {
-            case "WhileStatement":
-            case "DoWhileStatement":
-                return parent;
-
-            case "ForStatement":
-
-                // `init` is outside of the loop.
-                if (parent.init !== currentNode) {
-                    return parent;
-                }
-                break;
-
-            case "ForInStatement":
-            case "ForOfStatement":
-
-                // `right` is outside of the loop.
-                if (parent.right !== currentNode) {
-                    return parent;
-                }
-                break;
-
-            case "ArrowFunctionExpression":
-            case "FunctionExpression":
-            case "FunctionDeclaration":
-
-                // We don't need to check nested functions.
-                return null;
-
-            default:
-                break;
-        }
-    }
-
-    return null;
-}
 
 /**
- * Gets the containing loop node of a given node.
- * If the loop was nested, this returns the most outer loop.
- * @param {ASTNode} node A node to get. This is a loop node.
- * @param {ASTNode|null} excludedNode A node that the result node should not
- *      include.
- * @returns {ASTNode} The most outer loop node.
+ * Identifies is a node is a FunctionExpression which is part of an IIFE
+ * @param {ASTNode} node Node to test
+ * @returns {boolean} True if it's an IIFE
  */
-function getTopLoopNode(node, excludedNode) {
-    const border = excludedNode ? excludedNode.range[1] : 0;
-    let retv = node;
-    let containingLoopNode = node;
-
-    while (containingLoopNode && containingLoopNode.range[0] >= border) {
-        retv = containingLoopNode;
-        containingLoopNode = getContainingLoopNode(containingLoopNode);
-    }
-
-    return retv;
+function isIIFE(node) {
+    return (node.type === "FunctionExpression" || node.type === "ArrowFunctionExpression") && node.parent && node.parent.type === "CallExpression" && node.parent.callee === node;
 }
 
-/**
- * Checks whether a given reference which refers to an upper scope's variable is
- * safe or not.
- * @param {ASTNode} loopNode A containing loop node.
- * @param {eslint-scope.Reference} reference A reference to check.
- * @returns {boolean} `true` if the reference is safe or not.
- */
-function isSafe(loopNode, reference) {
-    const variable = reference.resolved;
-    const definition = variable && variable.defs[0];
-    const declaration = definition && definition.parent;
-    const kind = (declaration && declaration.type === "VariableDeclaration")
-        ? declaration.kind
-        : "";
-
-    // Variables which are declared by `const` is safe.
-    if (kind === "const") {
-        return true;
-    }
-
-    /*
-     * Variables which are declared by `let` in the loop is safe.
-     * It's a different instance from the next loop step's.
-     */
-    if (kind === "let" &&
-        declaration.range[0] > loopNode.range[0] &&
-        declaration.range[1] < loopNode.range[1]
-    ) {
-        return true;
-    }
-
-    /*
-     * WriteReferences which exist after this border are unsafe because those
-     * can modify the variable.
-     */
-    const border = getTopLoopNode(
-        loopNode,
-        (kind === "let") ? declaration : null
-    ).range[0];
-
-    /**
-     * Checks whether a given reference is safe or not.
-     * The reference is every reference of the upper scope's variable we are
-     * looking now.
-     *
-     * It's safe if the reference matches one of the following condition.
-     * - is readonly.
-     * - doesn't exist inside a local function and after the border.
-     * @param {eslint-scope.Reference} upperRef A reference to check.
-     * @returns {boolean} `true` if the reference is safe.
-     */
-    function isSafeReference(upperRef) {
-        const id = upperRef.identifier;
-
-        return (
-            !upperRef.isWrite() ||
-            variable.scope.variableScope === upperRef.from.variableScope &&
-            id.range[0] < border
-        );
-    }
-
-    return Boolean(variable) && variable.references.every(isSafeReference);
-}
 
 //------------------------------------------------------------------------------
 // Rule Definition
@@ -168,8 +44,147 @@ module.exports = {
 
     create(context) {
 
+        const SKIPPED_IIFE_NODES = new Set();
         const sourceCode = context.sourceCode;
 
+        /**
+         * Gets the containing loop node of a specified node.
+         *
+         * We don't need to check nested functions, so this ignores those, with the exception of IIFE.
+         * `Scope.through` contains references of nested functions.
+         * @param {ASTNode} node An AST node to get.
+         * @returns {ASTNode|null} The containing loop node of the specified node, or
+         *      `null`.
+         */
+        function getContainingLoopNode(node) {
+            for (let currentNode = node; currentNode.parent; currentNode = currentNode.parent) {
+                const parent = currentNode.parent;
+
+                switch (parent.type) {
+                    case "WhileStatement":
+                    case "DoWhileStatement":
+                        return parent;
+
+                    case "ForStatement":
+
+                        // `init` is outside of the loop.
+                        if (parent.init !== currentNode) {
+                            return parent;
+                        }
+                        break;
+
+                    case "ForInStatement":
+                    case "ForOfStatement":
+
+                        // `right` is outside of the loop.
+                        if (parent.right !== currentNode) {
+                            return parent;
+                        }
+                        break;
+
+                    case "ArrowFunctionExpression":
+                    case "FunctionExpression":
+                    case "FunctionDeclaration":
+
+                        // We need to check nested functions only in case of IIFE.
+                        if (SKIPPED_IIFE_NODES.has(parent)) {
+                            break;
+                        }
+
+                        return null;
+                    default:
+                        break;
+                }
+            }
+
+            return null;
+        }
+
+        /**
+         * Gets the containing loop node of a given node.
+         * If the loop was nested, this returns the most outer loop.
+         * @param {ASTNode} node A node to get. This is a loop node.
+         * @param {ASTNode|null} excludedNode A node that the result node should not
+         *      include.
+         * @returns {ASTNode} The most outer loop node.
+         */
+        function getTopLoopNode(node, excludedNode) {
+            const border = excludedNode ? excludedNode.range[1] : 0;
+            let retv = node;
+            let containingLoopNode = node;
+
+            while (containingLoopNode && containingLoopNode.range[0] >= border) {
+                retv = containingLoopNode;
+                containingLoopNode = getContainingLoopNode(containingLoopNode);
+            }
+
+            return retv;
+        }
+
+        /**
+         * Checks whether a given reference which refers to an upper scope's variable is
+         * safe or not.
+         * @param {ASTNode} loopNode A containing loop node.
+         * @param {eslint-scope.Reference} reference A reference to check.
+         * @returns {boolean} `true` if the reference is safe or not.
+         */
+        function isSafe(loopNode, reference) {
+            const variable = reference.resolved;
+            const definition = variable && variable.defs[0];
+            const declaration = definition && definition.parent;
+            const kind = (declaration && declaration.type === "VariableDeclaration")
+                ? declaration.kind
+                : "";
+
+            // Variables which are declared by `const` is safe.
+            if (kind === "const") {
+                return true;
+            }
+
+            /*
+             * Variables which are declared by `let` in the loop is safe.
+             * It's a different instance from the next loop step's.
+             */
+            if (kind === "let" &&
+                declaration.range[0] > loopNode.range[0] &&
+                declaration.range[1] < loopNode.range[1]
+            ) {
+                return true;
+            }
+
+            /*
+             * WriteReferences which exist after this border are unsafe because those
+             * can modify the variable.
+             */
+            const border = getTopLoopNode(
+                loopNode,
+                (kind === "let") ? declaration : null
+            ).range[0];
+
+            /**
+             * Checks whether a given reference is safe or not.
+             * The reference is every reference of the upper scope's variable we are
+             * looking now.
+             *
+             * It's safe if the reference matches one of the following condition.
+             * - is readonly.
+             * - doesn't exist inside a local function and after the border.
+             * @param {eslint-scope.Reference} upperRef A reference to check.
+             * @returns {boolean} `true` if the reference is safe.
+             */
+            function isSafeReference(upperRef) {
+                const id = upperRef.identifier;
+
+                return (
+                    !upperRef.isWrite() ||
+                    variable.scope.variableScope === upperRef.from.variableScope &&
+                    id.range[0] < border
+                );
+            }
+
+            return Boolean(variable) && variable.references.every(isSafeReference);
+        }
+
         /**
          * Reports functions which match the following condition:
          *
@@ -186,6 +201,23 @@ module.exports = {
             }
 
             const references = sourceCode.getScope(node).through;
+
+            // Check if the function is not asynchronous or a generator function
+            if (!(node.async || node.generator)) {
+                if (isIIFE(node)) {
+
+                    const isFunctionExpression = node.type === "FunctionExpression";
+
+                    // Check if the function is referenced elsewhere in the code
+                    const isFunctionReferenced = isFunctionExpression && node.id ? references.some(r => r.identifier.name === node.id.name) : false;
+
+                    if (!isFunctionReferenced) {
+                        SKIPPED_IIFE_NODES.add(node);
+                        return;
+                    }
+                }
+            }
+
             const unsafeRefs = references.filter(r => r.resolved && !isSafe(loopNode, r)).map(r => r.identifier.name);
 
             if (unsafeRefs.length > 0) {