Is this a bug?

[Elfstone]

On Thursday, 16 March 2023 at 03:40:04 UTC, Elfstone wrote:
> ```D
> struct Matrix(S, size_t M, size_t N)
> {
> }
>
> alias Vec3(S) = Matrix!(S, 3, 1);
>
> void main()
> {
>     import std.stdio;
>
>     writeln(is(Vec3!float == Matrix!(S, 3, 1), S)); // `alias` 
> `S` is defined here
>     writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S)); 
> // Error: declaration `S` is already defined
> }
> ```
>
> Even though the following code compiles.
>
> ```D
>     writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
>     writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
> ```

Oops, the above code compiles, because I added comments!!!

Now this really doesn't compile:

```D
struct Matrix(S, size_t M, size_t N)
{
}

alias Vec3(S) = Matrix!(S, 3, 1);

void main()
{
     import std.stdio;

     writeln(is(Vec3!float == Matrix!(S, 3, 1), S));
     writeln(is(Matrix!(float, 3, 1) == Matrix!(S, 3, 1), S));
}
```