GL_ARB_ES3_1_compatibility extension not supported

[baldurk]

For gl_HelperInvocation in desktop GLSL this was added in GL_ARB_ES3_1_compatibility which became core in GLSL version 450. The extension though is written against GL 4.4 and so should be usable in a GLSL version 440 shader with the appropriate #extension.

It looks like glslang currently doesn't allow this extension: https://godbolt.org/z/j49Po3oW8

#version 440 core

#extension GL_ARB_ES3_1_compatibility : require

layout(binding = 0) uniform foo
{
    vec4 data;
} bar;

layout(location = 0) out vec4 col;

void main() {
    col = gl_HelperInvocation ? vec4(0, 1, 0, 1) : vec4(1, 0, 0, 1);
}

As this produces an error:

<source>
<source>:3: '#extension' : extension not supported: GL_ARB_ES3_1_compatibility
<source>:3: '#extension' : extra tokens -- expected newline 
<source>:3: '' : compilation terminated 
3 compilation errors.  No code generated.

Hopefully I've understood the track of these extensions correctly and this should be allowed.

[arcady-lunarg]

I agree with your reading of the spec, the extension requires OpenGL 4.4 (i.e. GLSL 4.40) and was promoted to core in 4.50, but glslang should still support it. I think nobody got around to doing it because it was promoted to core relatively quickly.

[baldurk]

Yeh indeed it seems like mostly a non-issue but technically correct. I only noticed because I was aiming for minimum support necessary.