Warning on self assignment

[Arun Chandrasekaran via Digitalmars-d-learn]

So I was telling my colleague that D would warn on self 
assignment, but found that I was wrong.

https://run.dlang.io/is/HLhtek
```
module a;

import std.stdio;

void main() {
    string a;
    a = a;          // Can the compiler warn at this line that 
there is no effect?
    writeln(a);
    return;
}
```