feat: fix logic for top-level this in no-invalid-this and no-eval (#…

…15712)

* feat: fix logic for top-level `this` in no-invalid-this and no-eval

* add test with `this.eval` to no-invalid-this

* update docs to clarify `no-invalid-this`

docs/rules/no-invalid-this.md

@@ -1,14 +1,18 @@
 # no-invalid-this
 
-Disallows `this` keywords outside of classes or class-like objects.
+Disallows use of `this` in contexts where the value of `this` is `undefined`.
 
 Under the strict mode, `this` keywords outside of classes or class-like objects might be `undefined` and raise a `TypeError`.
 
 ## Rule Details
 
-This rule aims to flag usage of `this` keywords outside of classes or class-like objects.
+This rule aims to flag usage of `this` keywords in contexts where the value of `this` is `undefined`.
 
-Basically, this rule checks whether or not a function containing `this` keyword is a constructor or a method.
+Top-level `this` in scripts is always considered valid because it refers to the global object regardless of the strict mode.
+
+Top-level `this` in ECMAScript modules is always considered invalid because its value is `undefined`.
+
+For `this` inside functions, this rule basically checks whether or not the function containing `this` keyword is a constructor or a method. Note that arrow functions have lexical `this`, and that therefore this rule checks their enclosing contexts.
 
 This rule judges from following conditions whether or not the function is a constructor:
 
@@ -30,6 +34,7 @@ And this rule allows `this` keywords in functions below:
 
 And this rule always allows `this` keywords in the following contexts:
 
+* At the top level of scripts.
 * In class field initializers.
 * In class static blocks.
 
@@ -46,9 +51,6 @@ Examples of **incorrect** code for this rule in strict mode:
 
 "use strict";
 
-this.a = 0;
-baz(() => this);
-
 (function() {
     this.a = 0;
     baz(() => this);
@@ -69,11 +71,6 @@ foo(function() {
     baz(() => this);
 });
 
-obj.foo = () => {
-    // `this` of arrow functions is the outer scope's.
-    this.a = 0;
-};
-
 var obj = {
     aaa: function() {
         return function foo() {
@@ -98,6 +95,9 @@ Examples of **correct** code for this rule in strict mode:
 
 "use strict";
 
+this.a = 0;
+baz(() => this);
+
 function Foo() {
     // OK, this is in a legacy style constructor.
     this.a = 0;

lib/rules/no-eval.js

@@ -87,6 +87,7 @@ module.exports = {
                 upper: funcInfo,
                 node,
                 strict,
+                isTopLevelOfScript: false,
                 defaultThis: false,
                 initialized: strict
             };
@@ -222,12 +223,14 @@ module.exports = {
                     strict =
                         scope.isStrict ||
                         node.sourceType === "module" ||
-                        (features.globalReturn && scope.childScopes[0].isStrict);
+                        (features.globalReturn && scope.childScopes[0].isStrict),
+                    isTopLevelOfScript = node.sourceType !== "module" && !features.globalReturn;
 
                 funcInfo = {
                     upper: null,
                     node,
                     strict,
+                    isTopLevelOfScript,
                     defaultThis: true,
                     initialized: true
                 };
@@ -269,7 +272,8 @@ module.exports = {
                     );
                 }
 
-                if (!funcInfo.strict && funcInfo.defaultThis) {
+                // `this` at the top level of scripts always refers to the global object
+                if (funcInfo.isTopLevelOfScript || (!funcInfo.strict && funcInfo.defaultThis)) {
 
                     // `this.eval` is possible built-in `eval`.
                     report(node.parent);

lib/rules/no-invalid-this.js

@@ -1,5 +1,5 @@
 /**
- * @fileoverview A rule to disallow `this` keywords outside of classes or class-like objects.
+ * @fileoverview A rule to disallow `this` keywords in contexts where the value of `this` is `undefined`.
  * @author Toru Nagashima
  */
 
@@ -36,7 +36,7 @@ module.exports = {
         type: "suggestion",
 
         docs: {
-            description: "disallow `this` keywords outside of classes or class-like objects",
+            description: "disallow use of `this` in contexts where the value of `this` is `undefined`",
             recommended: false,
             url: "https://eslint.org/docs/rules/no-invalid-this"
         },
@@ -98,11 +98,11 @@ module.exports = {
                     const scope = context.getScope();
                     const features = context.parserOptions.ecmaFeatures || {};
 
+                    // `this` at the top level of scripts always refers to the global object
                     stack.push({
                         init: true,
                         node,
                         valid: !(
-                            scope.isStrict ||
                             node.sourceType === "module" ||
                             (features.globalReturn && scope.childScopes[0].isStrict)
                         )

tests/lib/rules/no-eval.js

@@ -42,6 +42,8 @@ ruleTester.run("no-eval", rule, {
         { code: "function foo() { var eval = 'foo'; globalThis[eval]('foo') }", env: { es2020: true } },
         "this.noeval('foo');",
         "function foo() { 'use strict'; this.eval('foo'); }",
+        { code: "'use strict'; this.eval('foo');", parserOptions: { ecmaFeatures: { globalReturn: true } } },
+        { code: "this.eval('foo');", parserOptions: { ecmaVersion: 6, sourceType: "module" } },
         { code: "function foo() { this.eval('foo'); }", parserOptions: { ecmaVersion: 6, sourceType: "module" } },
         { code: "function foo() { this.eval('foo'); }", parserOptions: { ecmaFeatures: { impliedStrict: true } } },
         "var obj = {foo: function() { this.eval('foo'); }}",
@@ -92,6 +94,7 @@ ruleTester.run("no-eval", rule, {
         { code: "(0, window['eval'])('foo')", env: { browser: true }, errors: [{ messageId: "unexpected", type: "MemberExpression", column: 12, endColumn: 18 }] },
         { code: "var EVAL = eval; EVAL('foo')", errors: [{ messageId: "unexpected", type: "Identifier", column: 12, endColumn: 16 }] },
         { code: "var EVAL = this.eval; EVAL('foo')", errors: [{ messageId: "unexpected", type: "MemberExpression", column: 17, endColumn: 21 }] },
+        { code: "'use strict'; var EVAL = this.eval; EVAL('foo')", errors: [{ messageId: "unexpected", type: "MemberExpression", column: 31, endColumn: 35 }] },
         { code: "(function(exe){ exe('foo') })(eval);", errors: [{ messageId: "unexpected", type: "Identifier", column: 31, endColumn: 35 }] },
         { code: "window.eval('foo')", env: { browser: true }, errors: [{ messageId: "unexpected", type: "CallExpression", column: 8, endColumn: 12 }] },
         { code: "window.window.eval('foo')", env: { browser: true }, errors: [{ messageId: "unexpected", type: "CallExpression", column: 15, endColumn: 19 }] },
@@ -100,6 +103,7 @@ ruleTester.run("no-eval", rule, {
         { code: "global.global.eval('foo')", env: { node: true }, errors: [{ messageId: "unexpected", type: "CallExpression", column: 15, endColumn: 19 }] },
         { code: "global.global[`eval`]('foo')", parserOptions: { ecmaVersion: 6 }, env: { node: true }, errors: [{ messageId: "unexpected", type: "CallExpression", column: 15, endColumn: 21 }] },
         { code: "this.eval('foo')", errors: [{ messageId: "unexpected", type: "CallExpression", column: 6, endColumn: 10 }] },
+        { code: "'use strict'; this.eval('foo')", errors: [{ messageId: "unexpected", type: "CallExpression", column: 20, endColumn: 24 }] },
         { code: "function foo() { this.eval('foo') }", errors: [{ messageId: "unexpected", type: "CallExpression", column: 23, endColumn: 27 }] },
         { code: "var EVAL = globalThis.eval; EVAL('foo')", env: { es2020: true }, errors: [{ messageId: "unexpected", type: "MemberExpression", column: 23, endColumn: 27 }] },
         { code: "globalThis.eval('foo')", env: { es2020: true }, errors: [{ messageId: "unexpected", type: "CallExpression", column: 12, endColumn: 16 }] },
@@ -134,6 +138,11 @@ ruleTester.run("no-eval", rule, {
             parserOptions: { ecmaVersion: 2022 },
             errors: [{ messageId: "unexpected" }]
         },
+        {
+            code: "'use strict'; class C { [this.eval('foo')] }",
+            parserOptions: { ecmaVersion: 2022 },
+            errors: [{ messageId: "unexpected" }]
+        },
 
         {
             code: "class A { static {} [this.eval()]; }",

tests/lib/rules/no-invalid-this.js

@@ -106,8 +106,8 @@ const patterns = [
         code: "console.log(this); z(x => console.log(x, this));",
         parserOptions: { ecmaVersion: 6 },
         errors,
-        valid: [NORMAL],
-        invalid: [USE_STRICT, IMPLIED_STRICT, MODULES]
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT],
+        invalid: [MODULES]
     },
     {
         code: "console.log(this); z(x => console.log(x, this));",
@@ -125,8 +125,17 @@ const patterns = [
             ecmaVersion: 6
         },
         errors,
-        valid: [NORMAL],
-        invalid: [USE_STRICT, IMPLIED_STRICT, MODULES]
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT],
+        invalid: [MODULES]
+    },
+    {
+        code: "this.eval('foo');",
+        parserOptions: {
+            ecmaVersion: 6
+        },
+        errors: [{ messageId: "unexpectedThis", type: "ThisExpression" }],
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT],
+        invalid: [MODULES]
     },
 
     // IIFE.
@@ -374,8 +383,8 @@ const patterns = [
     {
         code: "obj.foo = (() => () => { console.log(this); z(x => console.log(x, this)); })();",
         parserOptions: { ecmaVersion: 6 },
-        valid: [NORMAL],
-        invalid: [USE_STRICT, IMPLIED_STRICT, MODULES],
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT],
+        invalid: [MODULES],
         errors
     },
     {
@@ -793,8 +802,8 @@ const patterns = [
     {
         code: "class C { [this.foo]; }",
         parserOptions: { ecmaVersion: 2022 },
-        valid: [NORMAL], // the global this in non-strict mode is OK.
-        invalid: [USE_STRICT, IMPLIED_STRICT, MODULES],
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT], // `this` is the top-level `this`
+        invalid: [MODULES],
         errors: [{ messageId: "unexpectedThis", type: "ThisExpression" }]
     },
     {
@@ -855,15 +864,15 @@ const patterns = [
     {
         code: "class C { static {} [this]; }",
         parserOptions: { ecmaVersion: 2022 },
-        valid: [NORMAL],
-        invalid: [USE_STRICT, IMPLIED_STRICT, MODULES],
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT],
+        invalid: [MODULES],
         errors: [{ messageId: "unexpectedThis", type: "ThisExpression" }]
     },
     {
         code: "class C { static {} [this.x]; }",
         parserOptions: { ecmaVersion: 2022 },
-        valid: [NORMAL],
-        invalid: [USE_STRICT, IMPLIED_STRICT, MODULES],
+        valid: [NORMAL, USE_STRICT, IMPLIED_STRICT],
+        invalid: [MODULES],
         errors: [{ messageId: "unexpectedThis", type: "ThisExpression" }]
     },