Disallow initializers in for-in and for-of loops

src/compiler/checker.ts

@@ -10769,6 +10769,12 @@ module ts {
                             Diagnostics.Only_a_single_variable_declaration_is_allowed_in_a_for_of_statement;
                         return grammarErrorOnFirstToken(variableList.declarations[1], diagnostic);
                     }
+                    if (variableList.declarations[0].initializer) {
+                        var diagnostic = forInOrOfStatement.kind === SyntaxKind.ForInStatement ?
+                            Diagnostics.The_variable_declaration_of_a_for_in_statement_cannot_have_an_initializer :
+                            Diagnostics.The_variable_declaration_of_a_for_of_statement_cannot_have_an_initializer;
+                        return grammarErrorOnNode(variableList.declarations[0].name, diagnostic);
+                    }
                 }
             }
 

src/compiler/diagnosticInformationMap.generated.ts

@@ -148,6 +148,8 @@ module ts {
         A_rest_element_cannot_have_an_initializer: { code: 1186, category: DiagnosticCategory.Error, key: "A rest element cannot have an initializer." },
         A_parameter_property_may_not_be_a_binding_pattern: { code: 1187, category: DiagnosticCategory.Error, key: "A parameter property may not be a binding pattern." },
         Only_a_single_variable_declaration_is_allowed_in_a_for_of_statement: { code: 1188, category: DiagnosticCategory.Error, key: "Only a single variable declaration is allowed in a 'for...of' statement." },
+        The_variable_declaration_of_a_for_in_statement_cannot_have_an_initializer: { code: 1189, category: DiagnosticCategory.Error, key: "The variable declaration of a 'for...in' statement cannot have an initializer." },
+        The_variable_declaration_of_a_for_of_statement_cannot_have_an_initializer: { code: 1190, category: DiagnosticCategory.Error, key: "The variable declaration of a 'for...of' statement cannot have an initializer." },
         Duplicate_identifier_0: { code: 2300, category: DiagnosticCategory.Error, key: "Duplicate identifier '{0}'." },
         Initializer_of_instance_member_variable_0_cannot_reference_identifier_1_declared_in_the_constructor: { code: 2301, category: DiagnosticCategory.Error, key: "Initializer of instance member variable '{0}' cannot reference identifier '{1}' declared in the constructor." },
         Static_members_cannot_reference_class_type_parameters: { code: 2302, category: DiagnosticCategory.Error, key: "Static members cannot reference class type parameters." },

src/compiler/diagnosticMessages.json

@@ -583,6 +583,14 @@
         "category": "Error",
         "code": 1188
     },
+    "The variable declaration of a 'for...in' statement cannot have an initializer.": {
+        "category": "Error",
+        "code": 1189
+    },
+    "The variable declaration of a 'for...of' statement cannot have an initializer.": {
+        "category": "Error",
+        "code": 1190
+    },
 
     "Duplicate identifier '{0}'.": {
         "category": "Error",