Missing error if ClassDeclaration is used in Statement position

[ajafff]

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:

[RyanCavanaugh]

Locally-scoped enums are valid so the code isn't technically wrong but I can't see anyone doing that on purpose either

[ajafff]

@RyanCavanaugh

the code isn't technically wrong

If that's the case, I would expect that enum E is not visible outside of IfStatement.thenStatement. Otherwise this can cause hard to diagnose bugs.
And if the enum is not visible outside of its own declaration, there's no point in declaring it at all.

[nicdard]

I would like to try to help with this one