wgsl: validate assignment

[dj2]

Simple assignment

• vec.{x,y,z,w,r,g,b,a} = 1
• vec.xy = vec2(1) fails (no multi-swizzle on lhs)
• vec[0] = 1
• vec[-1] = 1 is not a validation error
• vec[99] = 1 is not a validation error
• ary[1] = 1
• ary[-1] = 1 is not a validation error
• ary[99] = 1 is not a validation error
• vec[min(max(1, 2), 1)] = 1
• struct.a = 1
• struct.a.b.c.d.e.r = 1
• *ptr = 1, write to a de-ref'd pointer
• structA = structB succeeds
• structA = structB validation error when structB has {runtime array, atomic, sampler?} (not constructable things)
• func().r = 1 where func returns a vec ... ?
• Assign where RHS type != LHS type is validation error
• Write to LHS where access mode is write fails
• Write to LHS in uniform address space fails
• Write to LHS in storage, read address space fails
• Write to {texture, sampler, pointer} fails
• RHS of {texture, sampler, pointer} fails validation (maybe the same as the above?)

Phony assignment

• RHS of {texture, sampler, pointer} succeed
• RHS of constructable passes
• RHS of non-constructable fails (struct with runtime array)
• RHS of function call

Compound assignment

• Compound assignment with space between the <char> and = fails parse
• Same set of tests as simple assignment
• Validate that e1 is only evaluated once (function call returning vec that increments global?)
• _ += 1 fails (for all compound types)

• https://www.w3.org/TR/WGSL/#assignment

[dj2]

I believe these are covered. We can fill individual issues for anything which is missing.