I am receiving the following error when calling "glLinkProgram" (so here I am):

> Internal error compiling shader with Metal backend.
> Please submit this shader, or website as a bug to https://bugs.webkit.org

I am trying compile and link an OpenGL ES 2.0 shader via ANGLE to Metal 
on Mac OS X. The same shader works fine via OpenGL ES directly (Mac OS X 
without ANGLE to Metal). Also, the same shader works fine for ANGLE to 
DirectX (Windows 10).

Something goes wrong when trying to link the shader via ANGLE to Metal!? 

**** VERTEX SHADER PART: 

#ifdef GL_ES                                         
  precision mediump float;                           
  #define TEXP mediump                               
  #define COLP lowp                                  
#else                                                
  #define TEXP                                       
  #define COLP                                       
#endif                                               
attribute vec4 a_pos;                                
attribute TEXP vec2 a_tex_uv;                        
attribute COLP vec4 a_col;                           
varying TEXP vec2 v_tex_uv;                          
varying COLP vec4 v_col;                             
void main()                                          
{                                                    
   gl_Position = a_pos;                              
   v_tex_uv = a_tex_uv;                              
   v_col = a_col;                                    
}                                                    

**** FRAGMENT SHADER PART:

#ifdef GL_ES                                         
  precision mediump float;                           
  #define TEXP mediump                               
  #define COLP lowp                                  
#else                                                
  #define TEXP                                       
  #define COLP                                       
#endif                                               
uniform sampler2D s_tex;                             
uniform float u_val;                                 
varying TEXP vec2 v_tex_uv;                          
varying COLP vec4 v_col;                             
void main()                                           
{                                                     
  gl_FragColor = texture2D(s_tex, v_tex_uv);          
  gl_FragColor *= v_col;                              
}                                                     
\