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

[ ] 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