prefer-module: Use suggestions for 'use strict' directive

rules/prefer-module.js

@@ -10,6 +10,7 @@ const {replaceReferenceIdentifier, removeSpacesAfter} = require('./fix/index.js'
 const ERROR_USE_STRICT_DIRECTIVE = 'error/use-strict-directive';
 const ERROR_GLOBAL_RETURN = 'error/global-return';
 const ERROR_IDENTIFIER = 'error/identifier';
+const SUGGESTION_USE_STRICT_DIRECTIVE = 'suggestion/use-strict-directive';
 const SUGGESTION_DIRNAME = 'suggestion/dirname';
 const SUGGESTION_FILENAME = 'suggestion/filename';
 const SUGGESTION_IMPORT = 'suggestion/import';
@@ -18,6 +19,7 @@ const messages = {
 	[ERROR_USE_STRICT_DIRECTIVE]: 'Do not use "use strict" directive.',
 	[ERROR_GLOBAL_RETURN]: '"return" should be used inside a function.',
 	[ERROR_IDENTIFIER]: 'Do not use "{{name}}".',
+	[SUGGESTION_USE_STRICT_DIRECTIVE]: 'Remove "use strict" directive.',
 	[SUGGESTION_DIRNAME]: 'Replace "__dirname" with `"…(import.meta.url)"`.',
 	[SUGGESTION_FILENAME]: 'Replace "__filename" with `"…(import.meta.url)"`.',
 	[SUGGESTION_IMPORT]: 'Switch to `import`.',
@@ -212,24 +214,29 @@ function fixModuleExports(node, sourceCode) {
 }
 
 function create(context) {
-	const filename = context.getFilename();
+	const filename = context.getFilename().toLowerCase();
 
-	if (filename.toLowerCase().endsWith('.cjs')) {
+	if (filename.endsWith('.cjs')) {
 		return {};
 	}
 
 	const sourceCode = context.getSourceCode();
 
 	return {
 		'ExpressionStatement[directive="use strict"]'(node) {
-			return {
-				node,
-				messageId: ERROR_USE_STRICT_DIRECTIVE,
-				* fix(fixer) {
-					yield fixer.remove(node);
-					yield removeSpacesAfter(node, sourceCode, fixer);
-				},
+			const problem = {node, messageId: ERROR_USE_STRICT_DIRECTIVE};
+			const fix = function * (fixer) {
+				yield fixer.remove(node);
+				yield removeSpacesAfter(node, sourceCode, fixer);
 			};
+
+			if (filename.endsWith('.mjs')) {
+				problem.fix = fix;
+			} else {
+				problem.suggest = [{messageId: SUGGESTION_USE_STRICT_DIRECTIVE, fix}];
+			}
+
+			return problem;
 		},
 		'ReturnStatement:not(:function ReturnStatement)'(node) {
 			return {

test/prefer-module.mjs

@@ -29,6 +29,14 @@ test.snapshot({
 				console.log(1);
 			}
 		`,
+		{
+			code: outdent`
+				'use strict';
+
+				console.log(1);
+			`,
+			filename: 'example.mjs',
+		},
 	],
 });
 

test/snapshots/prefer-module.mjs.md

@@ -9,39 +9,35 @@ Generated by [AVA](https://avajs.dev).
       2 |
       3 | console.log(1);
 
-> Output
-
-    `␊
-      1 | console.log(1);␊
-    `
-
 > Error 1/1
 
     `␊
     > 1 | 'use strict';␊
         | ^^^^^^^^^^^^^ Do not use "use strict" directive.␊
       2 |␊
       3 | console.log(1);␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Remove "use strict" directive.␊
+      1 | console.log(1);␊
     `
 
 ## Invalid #2
       1 | "use strict";
       2 |
       3 | console.log(1);
 
-> Output
-
-    `␊
-      1 | console.log(1);␊
-    `
-
 > Error 1/1
 
     `␊
     > 1 | "use strict";␊
         | ^^^^^^^^^^^^^ Do not use "use strict" directive.␊
       2 |␊
       3 | console.log(1);␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Remove "use strict" directive.␊
+      1 | console.log(1);␊
     `
 
 ## Invalid #3
@@ -50,22 +46,46 @@ Generated by [AVA](https://avajs.dev).
       3 | 	console.log(1);
       4 | }
 
-> Output
+> Error 1/1
 
     `␊
       1 | function foo () {␊
+    > 2 | 	"use strict";␊
+        | 	^^^^^^^^^^^^^ Do not use "use strict" directive.␊
+      3 | 	console.log(1);␊
+      4 | }␊
+    ␊
+    --------------------------------------------------------------------------------␊
+    Suggestion 1/1: Remove "use strict" directive.␊
+      1 | function foo () {␊
       2 | 	console.log(1);␊
       3 | }␊
     `
 
+## Invalid #4
+      1 | 'use strict';
+      2 |
+      3 | console.log(1);
+
+> Filename
+
+    `␊
+    example.mjs␊
+    `
+
+> Output
+
+    `␊
+      1 | console.log(1);␊
+    `
+
 > Error 1/1
 
     `␊
-      1 | function foo () {␊
-    > 2 | 	"use strict";␊
-        | 	^^^^^^^^^^^^^ Do not use "use strict" directive.␊
-      3 | 	console.log(1);␊
-      4 | }␊
+    > 1 | 'use strict';␊
+        | ^^^^^^^^^^^^^ Do not use "use strict" directive.␊
+      2 |␊
+      3 | console.log(1);␊
     `
 
 ## Invalid #1