Fix: error on multiple super classes (fixes #493) (#494)

Author: ikatyang

lib/ast-converter.js

@@ -26,13 +26,7 @@ const convert = require("./convert"),
  * @returns {Object}       converted error object
  */
 function convertError(error) {
-    const loc = error.file.getLineAndCharacterOfPosition(error.start);
-    return {
-        index: error.start,
-        lineNumber: loc.line + 1,
-        column: loc.character,
-        message: error.message || error.messageText
-    };
+    return nodeUtils.createError(error.file, error.start, error.message || error.messageText);
 }
 
 //------------------------------------------------------------------------------

lib/convert.js

@@ -1397,8 +1397,14 @@ module.exports = function convert(config) {
             const openBrace = nodeUtils.findNextToken(lastClassToken, ast);
             const superClass = heritageClauses.find(clause => clause.token === SyntaxKind.ExtendsKeyword);
 
-            if (superClass && superClass.types[0] && superClass.types[0].typeArguments) {
-                result.superTypeParameters = convertTypeArgumentsToTypeParameters(superClass.types[0].typeArguments);
+            if (superClass) {
+                if (superClass.types.length > 1) {
+                    throw nodeUtils.createError(ast, superClass.types[1].pos, "Classes can only extend a single class.");
+                }
+
+                if (superClass.types[0] && superClass.types[0].typeArguments) {
+                    result.superTypeParameters = convertTypeArgumentsToTypeParameters(superClass.types[0].typeArguments);
+                }
             }
 
             const implementsClause = heritageClauses.find(clause => clause.token === SyntaxKind.ImplementsKeyword);

lib/node-utils.js

@@ -191,7 +191,8 @@ module.exports = {
     isWithinTypeAnnotation,
     isTypeKeyword,
     isComment,
-    isJSDocComment
+    isJSDocComment,
+    createError
 };
 /* eslint-enable no-use-before-define */
 
@@ -767,3 +768,19 @@ function getNodeContainer(ast, start, end) {
 
     return container;
 }
+
+/**
+ * @param {Object} ast     the AST object
+ * @param {int} start      the index at which the error starts
+ * @param {string} message the error message
+ * @returns {Object}       converted error object
+ */
+function createError(ast, start, message) {
+    const loc = ast.getLineAndCharacterOfPosition(start);
+    return {
+        index: start,
+        lineNumber: loc.line + 1,
+        column: loc.character,
+        message
+    };
+}

tests/fixtures/ecma-features/classes/invalid-class-two-super-classes.src.js

@@ -0,0 +1 @@
+class A extends B, C {}

tests/lib/__snapshots__/ecma-features.js.snap

@@ -22287,6 +22287,8 @@ Object {
 }
 `;
 
+exports[`ecmaFeatures fixtures/classes/invalid-class-two-super-classes.src 1`] = `"Classes can only extend a single class."`;
+
 exports[`ecmaFeatures fixtures/classes/named-class-expression.src 1`] = `
 Object {
   "body": Array [