How would I set sampler2D uniforms in OpenGL in a SPIR-V Shader?

I am compiling this shader with glslangValidator, and am using OpenGL 4.3 Core Profile with the extension GL_ARB_gl_spirv, and using the GLAD webservice to generate function pointers to access the Core OpenGL API, and SDL2 to create the context, if that is of any use.

If I have a fragment shader like so:

#version 430 core

//output Fragment Color
layout (location = 0) out vec4 outFragColor;

//Texture coordinates passed from the vertex shader
layout (location = 0) in vec2 inTexCoord;

uniform sampler2D inTexture;

void main()
{
    outFragColor = texture(inTexture, inTexCoord);
}

How would I be able to set which texture unit inTexture uses?

From what I have read online through documents, I cannot use glGetUniformLocation to get the location of this uniform to use in glUniform1i, because of the fact I am using SPIR-V, instead of GLSL directly.

What would I need to do to set it in a fashion like glUniform1i? Do I need to set the location in the layout modifier? The binding? I've tried to use Uniform Buffer Objects, but apparently sampler2D can only be a uniform.

Solution

Since GLSL 4.20, you have the ability to set the binding point for any opaque type like samplers from GLSL code directly. This is done through the binding layout qualifier:

layout(binding = #) uniform sampler2D inTexture;

The # here is whatever binding index you want to use. This is the index you use when binding the texture: glActiveTexture(GL_TEXTURE0 + #). That is, you don't need to use glProgramUniform to set the uniform's value anymore; you already set it in the shader.

If you want to modify the binding dynamically (and you shouldn't), GLSL 4.30 offers the ability to set the location for any non-block uniform value via the location layout qualifier:

layout(location = #) uniform sampler2D inTexture;

This makes # the uniform's location, which you can pass to any glProgramUniform call.