ANGLE AST Validation Bypass

Shader source (262 byte reproducer)

#version 300 es
precision mediump float;
int u0mode; out vec4 fragOut;
void main(){
  vec4 c = vec4(0);
  for(int i=0;i<0;i++){ if(0==u0mode){break;} }
  switch(u0mode){ case 0: case 1: ; }
  switch(u0mode){
    case 0: break;
      vec4 c = vec4(0);
      for(int i=0;i<0;i++) fragOut.g=.0;
    default: c.a=.0;
  }
}

Translated source (live — from this browser via WEBGL_debug_shaders)

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Standalone analysis — malformed output evidence (static — from offline ANGLE translator analysis)

HLSL output (D3D path):
switch (_u0mode) {
  case (0):
    break;
  default:
    (_c3006.w = 0.0);    // UNDECLARED — declaration was dropped
    break;
}

ESSL output:
switch (_uu0mode) {
  case (0):
    break;
  default:
    (_uc.w = 0.0);       // UNDECLARED — same corruption
}

GLSL 4.50 output:
switch (_uu0mode) {
  case (0):
    break;
  default:
    (_uc.w = 0.0);       // UNDECLARED — same corruption
}

In all cases ANGLE returns compilation success while emitting
code referencing variables (_c3006 / _uc) that are never declared.