In #600 it seems we've coalesced around the first line of the shader being something like #version foobar (like GLSL). Will we use a similar mechanism for opting into shading language extensions?

If the answer is "yes," that means that extensions will be per-shader-module. However, there might be appetite for enabling/disabling extensions on a per-entry-point level.

If extensions are per-entry-point, we'd have to figure out what happens when a vertex shader with one set of extensions gets linked to a fragment shader with a different set of extensions. (Maybe the answer to this is extension-specific?)

If extensions are per-entry-point, how will extensions modify "what it means to be an entry point," like a possible ray tracing extension?