Fix: vars-on-top crashs at export declarations (fixes #6210) (#6220)

Author: mysticatea

lib/rules/vars-on-top.js

@@ -46,6 +46,23 @@ module.exports = {
                 node.type === "ImportDefaultSpecifier" || node.type === "ImportNamespaceSpecifier";
         }
 
+        /**
+         * Checks whether a given node is a variable declaration or not.
+         *
+         * @param {ASTNode} node - any node
+         * @returns {boolean} `true` if the node is a variable declaration.
+         */
+        function isVariableDeclaration(node) {
+            return (
+                node.type === "VariableDeclaration" ||
+                (
+                    node.type === "ExportNamedDeclaration" &&
+                    node.declaration &&
+                    node.declaration.type === "VariableDeclaration"
+                )
+            );
+        }
+
         /**
          * Checks whether this variable is on top of the block body
          * @param {ASTNode} node - The node to check
@@ -64,9 +81,7 @@ module.exports = {
             }
 
             for (; i < l; ++i) {
-                if (statements[i].type !== "VariableDeclaration" &&
-                        (statements[i].type !== "ExportNamedDeclaration" ||
-                        statements[i].declaration.type !== "VariableDeclaration")) {
+                if (!isVariableDeclaration(statements[i])) {
                     return false;
                 }
                 if (statements[i] === node) {

tests/lib/rules/vars-on-top.js

@@ -457,6 +457,40 @@ ruleTester.run("vars-on-top", rule, {
                 sourceType: "module"
             },
             errors: [{message: "All 'var' declarations must be at the top of the function scope.", type: "VariableDeclaration"}]
+        },
+        {
+            code: [
+                "import {foo} from 'foo';",
+                "export {foo};",
+                "var test = 1;"
+            ].join("\n"),
+            parserOptions: {
+                ecmaVersion: 6,
+                sourceType: "module"
+            },
+            errors: [{message: "All 'var' declarations must be at the top of the function scope.", type: "VariableDeclaration"}]
+        },
+        {
+            code: [
+                "export {foo} from 'foo';",
+                "var test = 1;"
+            ].join("\n"),
+            parserOptions: {
+                ecmaVersion: 6,
+                sourceType: "module"
+            },
+            errors: [{message: "All 'var' declarations must be at the top of the function scope.", type: "VariableDeclaration"}]
+        },
+        {
+            code: [
+                "export * from 'foo';",
+                "var test = 1;"
+            ].join("\n"),
+            parserOptions: {
+                ecmaVersion: 6,
+                sourceType: "module"
+            },
+            errors: [{message: "All 'var' declarations must be at the top of the function scope.", type: "VariableDeclaration"}]
         }
     ]
 });