[glsl-in] naga panic: index out of bound in swizzle expression

[Vipitis]

I encountered this panic while working with shadertoys through wgpu-py. The original shader where this happened: https://www.shadertoy.com/view/clB3D3 and a minimal reconstruction: https://www.shadertoy.com/view/cltfRn

case that panics:

#define MIX2(c) mix(c.xy, c.xy, 0.5)
const vec2 blank = MIX2(vec2(0.0,1.0));
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = fragCoord/iResolution.xy;
    vec2 col = MIX2(uv);
    fragColor = vec4(col,0.0,1.0);
}

equivalent case that works (comment out the unused const)

#define MIX2(c) mix(c.xy, c.xy, 0.5)
// const vec2 blank = MIX2(vec2(0.0,1.0));
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = fragCoord/iResolution.xy;
    vec2 col = MIX2(uv);
    fragColor = vec4(col,0.0,1.0);
}

equivalent case that throws an error without swizzle (error might be with the implementation, but at least it doesn't panic)

#define MIX2(c) mix(c, c, 0.5)
const vec2 blank = MIX2(vec2(0.0,1.0));
void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    vec2 uv = fragCoord/iResolution.xy;
    vec2 col = MIX2(uv);
    fragColor = vec4(col,0.0,1.0);
}

I used naga-cli 0.14.0 and wgpu-py shadertoy util to add the compatibility code for shadertoy syntax.

Full error trace:

naga panic_shader4.frag 
thread 'main' panicked at ~\.cargo\registry\src\index.crates.io-6f17d22bba15001f\naga-0.14.0\src\front\glsl\variables.rs:336:28:
index out of bounds: the len is 12 but the index is 15
stack backtrace:
   0:     0x7ff6c169c3da - <unknown>
   1:     0x7ff6c16b4acb - <unknown>
   2:     0x7ff6c16992e1 - <unknown>
   3:     0x7ff6c169c15a - <unknown>
   4:     0x7ff6c169e75a - <unknown>
   5:     0x7ff6c169e3c8 - <unknown>
   6:     0x7ff6c169ee0e - <unknown>
   7:     0x7ff6c169ecfd - <unknown>
   8:     0x7ff6c169cdc9 - <unknown>
   9:     0x7ff6c169ea00 - <unknown>
  10:     0x7ff6c16d7b35 - <unknown>
  11:     0x7ff6c16d7cae - <unknown>
  12:     0x7ff6c15818a9 - <unknown>
  13:     0x7ff6c1527077 - <unknown>
  14:     0x7ff6c15746b5 - <unknown>
  15:     0x7ff6c15277bc - <unknown>
  16:     0x7ff6c1525d2d - <unknown>
  17:     0x7ff6c15ed931 - <unknown>
  18:     0x7ff6c15ee8b9 - <unknown>
  19:     0x7ff6c15f02bd - <unknown>
  20:     0x7ff6c15ff25d - <unknown>
  21:     0x7ff6c158308f - <unknown>
  22:     0x7ff6c13effb5 - <unknown>
  23:     0x7ff6c13fd636 - <unknown>
  24:     0x7ff6c13fd64c - <unknown>
  25:     0x7ff6c1693348 - <unknown>
  26:     0x7ff6c13f4f8c - <unknown>
  27:     0x7ff6c16bca68 - <unknown>
  28:     0x7ffd609e7344 - BaseThreadInitThunk
  29:     0x7ffd60b226b1 - RtlUserThreadStart

the perma link to the line it mentions:

wgpu/naga/src/front/glsl/variables.rs

Line 320 in ebcfd25

} = ctx[expression]