Missing error if ClassDeclaration is used in Statement position

TypeScript Version: 2.8.0-dev.20180318

Search Terms: class statement

Code

let codition = false as boolean;

if (condition)
    class C {} // runtime error if transpiled to ES2015 or above: Unexpected token class
if (condition)
    enum E { Foo } // should probably be an error?

new C(); // runtime error if transpiled to ES5, because 'C' is undefined
E.Foo; // runtime error: cannot read property 'Foo' of 'E'

Expected behavior:

Expected a compile error on class C and maybe on enum E

Actual behavior:
no error for these declarations, instead I get a runtime error when targeting ES2015 or above.

Playground Link:

Related Issues:

首先，使用指定的 TypeScript 版本和编译器目标重现所提供的条件类和 enum 示例。跟踪语句位置中的声明是如何被解析和检查的，然后验证无效情况会产生编译错误，而有效的声明上下文不受影响。