Do GLSL code snippets stored in named strings have to be compileable code to #include via ARB_shading_language_include extension? - opengl

Question

I learned how to use https://registry.khronos.org/OpenGL/extensions/ARB/ARB_shading_language_include.txt extension thanks to opengl - How to Using the #include in glsl support ARB_shading_language_include - Stack Overflow. I prepared the following named string and shader:
option A
// NamedString /lib/VertexData.glsl
struct VertexData {
vec3 objectPosition;
vec3 worldPosition;
};
VertexData fillVertexData() {
VertexData v;
v.objectPosition = objectPosition;
v.worldPosition = vec3(worldFromObject * vec4(objectPosition, 1));
return v
}
// MyShader.vert
#version 430
#extension GL_ARB_shading_language_include : require
layout(location = 0) in vec3 objectPosition;
uniform mat4 worldFromObject; // Model
uniform mat4 viewFromWorld; // View
uniform mat4 projectionFromView; // Projection
#include "/lib/VertexData.glsl"
out VertexData v;
void main() {
v = fillVertexData();
gl_Position = projectionFromView * viewFromWorld * vec4(v.worldPosition, 1);
}
When compiling the shader via glCompileShaderIncludeARB(vertex, 0, NULL, NULL); I get following error: Error. Message: 0:18(21): error: 'objectPosition' undeclared. The objectPosition vertex attribute declared in MyShader.vert is not recognized.
Whereas if I move the fillVertexData() function to MyShader.vert shader, it works fine.
option B
// NamedString /lib/VertexData.glsl
struct VertexData {
vec3 objectPosition;
vec3 worldPosition;
};
// MyShader.vert
#version 430
#extension GL_ARB_shading_language_include : require
layout(location = 0) in vec3 objectPosition;
uniform mat4 worldFromObject; // Model
uniform mat4 viewFromWorld; // View
uniform mat4 projectionFromView; // Projection
#include "/lib/VertexData.glsl"
out VertexData v;
VertexData fillVertexData() {
VertexData v;
v.objectPosition = objectPosition;
v.worldPosition = vec3(worldFromObject * vec4(objectPosition, 1));
return v
}
void main() {
v = fillVertexData();
gl_Position = projectionFromView * viewFromWorld * vec4(v.worldPosition, 1);
}
This made me think that the extension checks the scope of variables per named string. But that's not the behavior I expect from an #include preprocessor macro system. It should NOT care about variable scopes and just preprocess MyShader.vert and compile that one.
I tried option A via GL_GOOGLE_include_directive and glslangValidator -l MyShader.vert does NOT throw any errors for both options, and generated GLSL code via -E looks correct. Which was my expectation.
I read the extension specifications and it didn't mention that variables that are used in a named string should be declared by the time the extension is processing that named string. Am I doing something wrong? Or is this by design of ARB_shading_language_extension? Any suggestions on how I can keep fillVertexData() in the named string?
By the way, before writing my own #include implementation for my own app, I wanted to exhaust existing solutions. I first tried glslang library. But the preprocessor output I get from it is not compileable GLSL: my version of OpenGL does not support GL_GOOGLE_include_directive and it fills the code with #line directives where the second parameter is NOT an integer but a string (filename) which is not valid GLSL.
Using ARB_shading_language_extension was my second attempt of having reusable GLSL code via #includes.