fix: syntax error in prefer-arrow-callback autofix

lib/rules/prefer-arrow-callback.js

@@ -335,6 +335,7 @@ module.exports = {
                             // Convert the function expression to an arrow function.
                             const functionToken = sourceCode.getFirstToken(node, node.async ? 1 : 0);
                             const leftParenToken = sourceCode.getTokenAfter(functionToken, astUtils.isOpeningParenToken);
+                            const tokenBeforeBody = sourceCode.getTokenBefore(node.body);
 
                             if (sourceCode.commentsExistBetween(functionToken, leftParenToken)) {
 
@@ -348,7 +349,7 @@ module.exports = {
                                 // Remove extra tokens and spaces.
                                 yield fixer.removeRange([functionToken.range[0], leftParenToken.range[0]]);
                             }
-                            yield fixer.insertTextBefore(node.body, "=> ");
+                            yield fixer.insertTextAfter(tokenBeforeBody, " =>");
 
                             // Get the node that will become the new arrow function.
                             let replacedNode = callbackInfo.isLexicalThis ? node.parent.parent : node;

tests/lib/rules/prefer-arrow-callback.js

@@ -205,6 +205,46 @@ ruleTester.run("prefer-arrow-callback", rule, {
             code: "foo((function() { return this; }?.bind)(this));",
             output: null,
             errors
+        },
+
+        // https://github.com/eslint/eslint/issues/16718
+        {
+            code: `
+            test(
+                function ()
+                { }
+            );
+            `,
+            output: `
+            test(
+                () =>
+                { }
+            );
+            `,
+            errors
+        },
+        {
+            code: `
+            test(
+                function (
+                    ...args
+                ) /* Lorem ipsum
+                dolor sit amet. */ {
+                    return args;
+                }
+            );
+            `,
+            output: `
+            test(
+                (
+                    ...args
+                ) => /* Lorem ipsum
+                dolor sit amet. */ {
+                    return args;
+                }
+            );
+            `,
+            errors
         }
     ]
 });