[wgsl-in] Error on param redefinition

[SparkyPotato]

Previously,

fn x(a: f32, a: vec2<f32>) {}

was silently accepted by naga, binding the second parameter to a.

Now, it errors with

error: redefinition of `a`
  ┌─ ..\naga tests\wgsl.wgsl:1:6
  │
1 │ fn x(a: f32, a: vec2<f32>) {}
  │      ^       ^ redefinition of `a`
  │      │
  │      previous definition of `a`

[teoxoy]

Thanks for the PR; it looks good!

I think this would fix #2312 as well; would you mind adding one more test case for it?

[SparkyPotato]

Thanks for the PR; it looks good!

I think this would fix #2312 as well; would you mind adding one more test case for it?

The issue there was that we were pushing a scope for the arguments, and then another for the block. I fixed that by not using self.block, and commenting the reason why so we don't end up with a regression during future refactoring.

[teoxoy]

Looks good, thanks!