feat: support explicit resource management in no-loop-func (#19895)

mdjermanovic · web-flow · commit a6a63259de6c · 2025-07-04T06:40:19.000+02:00
* feat: support explicit resource management in `no-loop-func`

* replace tabs with spaces
diff --git a/docs/src/rules/no-loop-func.md b/docs/src/rules/no-loop-func.md
@@ -115,6 +115,34 @@ for (let i=10; i; i--) {
     a();
 }
 
+for (const i of foo) {
+    var a = function() { return i; }; // OK, all references are referring to block scoped variables in the loop.
+    a();
+}
+
+for (using i of foo) {
+    var a = function() { return i; }; // OK, all references are referring to block scoped variables in the loop.
+    a();
+}
+
+for (var i=10; i; i--) {
+    const foo = getsomething(i);
+    var a = function() { return foo; }; // OK, all references are referring to block scoped variables in the loop.
+    a();
+}
+
+for (var i=10; i; i--) {
+    using foo = getsomething(i);
+    var a = function() { return foo; }; // OK, all references are referring to block scoped variables in the loop.
+    a();
+}
+
+for (var i=10; i; i--) {
+    await using foo = getsomething(i);
+    var a = function() { return foo; }; // OK, all references are referring to block scoped variables in the loop.
+    a();
+}
+
 var foo = 100;
 for (let i=10; i; i--) {
     var a = function() { return foo; }; // OK, all references are referring to never modified variables.
diff --git a/lib/rules/no-loop-func.js b/lib/rules/no-loop-func.js
@@ -9,6 +9,8 @@
 // Helpers
 //------------------------------------------------------------------------------
 
+const CONSTANT_BINDINGS = new Set(["const", "using", "await using"]);
+
 /**
  * Identifies is a node is a FunctionExpression which is part of an IIFE
  * @param {ASTNode} node Node to test
@@ -148,8 +150,8 @@ module.exports = {
 					? declaration.kind
 					: "";
 
-			// Variables which are declared by `const` is safe.
-			if (kind === "const") {
+			// Constant variables are safe.
+			if (CONSTANT_BINDINGS.has(kind)) {
 				return true;
 			}
 
diff --git a/tests/lib/rules/no-loop-func.js b/tests/lib/rules/no-loop-func.js
@@ -50,6 +50,22 @@ ruleTester.run("no-loop-func", rule, {
 			code: "for (const i of {}) { (function() { i; }) }",
 			languageOptions: { ecmaVersion: 6 },
 		},
+		{
+			code: "for (using i of foo) { (function() { i; }) }",
+			languageOptions: { ecmaVersion: 2026 },
+		},
+		{
+			code: "for (await using i of foo) { (function() { i; }) }",
+			languageOptions: { ecmaVersion: 2026 },
+		},
+		{
+			code: "for (var i = 0; i < 10; ++i) { using foo = bar(i); (function() { foo; }) }",
+			languageOptions: { ecmaVersion: 2026 },
+		},
+		{
+			code: "for (var i = 0; i < 10; ++i) { await using foo = bar(i); (function() { foo; }) }",
+			languageOptions: { ecmaVersion: 2026 },
+		},
 		{
 			code: "for (let i = 0; i < 10; ++i) { for (let x in xs.filter(x => x != i)) {  } }",
 			languageOptions: { ecmaVersion: 6 },
@@ -170,7 +186,7 @@ ruleTester.run("no-loop-func", rule, {
                 current.c;
                 current.d;
             })();
-            
+
             current = current.upper;
             }
             `,
@@ -208,6 +224,42 @@ ruleTester.run("no-loop-func", rule, {
             `,
 			languageOptions: { ecmaVersion: 6 },
 		},
+		{
+			code: `
+            const foo = bar;
+
+            for (var i = 0; i < 5; i++) {
+                arr.push(() => foo);
+            }
+
+			foo = baz; // This is a runtime error, but not concern of this rule. For this rule, variable 'foo' is constant.
+            `,
+			languageOptions: { ecmaVersion: 6 },
+		},
+		{
+			code: `
+            using foo = bar;
+
+            for (var i = 0; i < 5; i++) {
+                arr.push(() => foo);
+            }
+
+			foo = baz; // This is a runtime error, but not concern of this rule. For this rule, variable 'foo' is constant.
+            `,
+			languageOptions: { ecmaVersion: 2026 },
+		},
+		{
+			code: `
+            await using foo = bar;
+
+            for (var i = 0; i < 5; i++) {
+                arr.push(() => foo);
+            }
+
+			foo = baz; // This is a runtime error, but not concern of this rule. For this rule, variable 'foo' is constant.
+            `,
+			languageOptions: { ecmaVersion: 2026 },
+		},
 	],
 	invalid: [
 		{
@@ -471,7 +523,7 @@ ruleTester.run("no-loop-func", rule, {
                     current;
                     arr.push(f);
                 })();
-                
+
                 current = current.upper;
             }
             `,
@@ -615,7 +667,7 @@ ruleTester.run("no-loop-func", rule, {
 
             for (var i = 0; i < 5; i++) {
                 arr.push((() => {
-                    return () => 
+                    return () =>
                         (() => i)();
                 })());
             }
@@ -666,7 +718,7 @@ ruleTester.run("no-loop-func", rule, {
                         return i;
                     })();
                 })();
-            
+
             }
             `,
 			languageOptions: { ecmaVersion: 2022 },
@@ -839,7 +891,7 @@ ruleTesterTypeScript.run("no-loop-func", rule, {
       // ConfiguredType is in globals, UnconfiguredType is not
       // Both should be considered safe as they are type references
       const process = (configItem: ConfiguredType, unconfigItem: UnconfiguredType) => {
-        return { 
+        return {
           config: configItem.value,
           unconfig: unconfigItem.value
         };
@@ -892,14 +944,14 @@ ruleTesterTypeScript.run("no-loop-func", rule, {
     id: number;
     name: string;
   }
-  
+
   const items: Item[] = [];
   for (var i = 0; i < 10; i++) {
     items.push({
       id: i,
       name: "Item " + i
     });
-    
+
     const process = function(callback: (item: Item) => void): void {
       callback({ id: i, name: "Item " + i });
     };
@@ -916,7 +968,7 @@ ruleTesterTypeScript.run("no-loop-func", rule, {
 		{
 			code: `
   type Processor<T> = (item: T) => void;
-		
+
   for (var i = 0; i < 10; i++) {
     const processor: Processor<number> = (item) => {
       return item + i;
