WGSL: const declarations in function scope cannot be used as const expressions

[ErichDonGubler]

Description

const-declared values in function scope (i.e., "local" const mySize = 2 inside a fn declaration) cannot be used in contexts where values must be constant-evaluatable, like array sizes.

Repro steps

1. Observe that while this passes validation in WGSL:

   const myArraySize = 2;
   @compute @workgroup_size(1, 1)
   fn main() {
   	var myArray: array<f32, myArraySize>;
   }

   …this does not:

   @compute @workgroup_size(1, 1)
   fn main() {
   	const myArraySize = 2; // Hello, I moved here!
   	var myArray: array<f32, myArraySize>;
   }

   …which returns an error from naga-cli:

   error: this operation is not supported in a const context
     ┌─ ../in.wgsl:4:26
     │
   4 │     var myArray: array<f32, myArraySize>;
     │                             ^^^^^^^^^^^ operation not supported here
   

Expected vs observed behavior

I expect that values bound to const declarations should be usable as a const expression in the same contexts, independent of where they are declared (lexical scoping notwithstanding).

[sagudev]

Indeed, I will check whats wrong.

[sagudev]

The problem is that we pass global ctx when resolving type:

wgpu/naga/src/front/wgsl/lower/mod.rs

Line 1455 in 3bcfe84

v.ty.map(|ast| self.resolve_ast_type(ast, &mut ctx.as_global()))