Disallow generators in an ambient context

src/compiler/checker.ts

@@ -12550,6 +12550,9 @@ module ts {
                     node.kind === SyntaxKind.FunctionDeclaration ||
                     node.kind === SyntaxKind.FunctionExpression ||
                     node.kind === SyntaxKind.MethodDeclaration);
+                if (isInAmbientContext(node)) {
+                    return grammarErrorOnNode(node.asteriskToken, Diagnostics.Generators_are_not_allowed_in_an_ambient_context);
+                }
                 if (languageVersion < ScriptTarget.ES6) {
                     return grammarErrorOnNode(node.asteriskToken, Diagnostics.Generators_are_only_available_when_targeting_ECMAScript_6_or_higher);
                 }

src/compiler/diagnosticInformationMap.generated.ts

@@ -175,6 +175,7 @@ module ts {
         Type_expected_0_is_a_reserved_word_in_strict_mode_Class_definitions_are_automatically_in_strict_mode: { code: 1216, category: DiagnosticCategory.Error, key: "Type expected. '{0}' is a reserved word in strict mode. Class definitions are automatically in strict mode." },
         Export_assignment_is_not_supported_when_module_flag_is_system: { code: 1218, category: DiagnosticCategory.Error, key: "Export assignment is not supported when '--module' flag is 'system'." },
         Generators_are_only_available_when_targeting_ECMAScript_6_or_higher: { code: 1219, category: DiagnosticCategory.Error, key: "Generators are only available when targeting ECMAScript 6 or higher." },
+        Generators_are_not_allowed_in_an_ambient_context: { code: 1220, category: DiagnosticCategory.Error, key: "Generators are not allowed in an ambient context." },
         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

@@ -687,6 +687,10 @@
         "category": "Error",
         "code": 1219
     },
+    "Generators are not allowed in an ambient context.": {
+        "category": "Error",
+        "code": 1220
+    },
 
 
     "Duplicate identifier '{0}'.": {