cc @alyssais

Why the ping, sorry?

This attempts to address the stability issues we previously discussed in #51672.

glslang is handled a bit oddly because it has three different sources, all of which must be overridden simultaneously by e.g. vulkan-validation-layers. I'd prefer to do this in a way that uses the overrideAttrs pattern and doesn't force callers to invoke callPackage and thereby complicate overriding dependencies, but it's not clear to me how to do that.

I'd do it like this:

glslang.override {
  spirv-tools = …;
}.overrideAttrs ({ ... }: {
  version = …;
  src = fetchFromGitHub { … };
})

The stable releases of spirv-* aren't used by the stable release of glslang. If we override them within glslang's expression, then downstream packages which need different overrides break, and it's not clear to me how to write a wrapper expression that's better than what I've already got here.

Any thoughts? Was hoping to get this in for 19.03.

If the glslang expression looks like:

{ spirv-headers, ... }:
let spirv-headers = spirv-headers.overrideAttrs (...);
...

then a caller cannot usefully do

glslang.override { spirv-headers = spirv-headers.overrideAttrs (...); }

because the override will be clobbered inside glslang's expression. Unfortunately, the stable version of spirv-*, the versions of spirv-* used by the stable version of glslang itself, and the versions of spirv-* used with glslang by packages that depend on glslang are all different.

One option would be to pass the necessary overridden dependencies in from all-packages.nix; this would be unconventional, and take up a lot more space in an already-massive file, but it'd allow for a more conventional structure.

The latest commit fixes a regression I discovered that's present in master (and presumably 19.03). It can be easily worked around by depending on vulkan-headers directly. Perhaps we should be using propagatedBuildInputs for that in the first place?

In all-packages.nix:

glslang = callPackage ../development/compilers/glslang {
  spirv-tools = spirv-tools.overrideAttrs (_: {
    src = fetchFromGitHub { ... };
  });
  spirv-headers = spirv-tools.overrideAttrs (_: {
    src = fetchFromGitHub { ... };
  });
};

Then glslang/default.nix would be totally conventional.

Drafted the proposed changes, and further bumped the versions while I was at it.

Is this blocked?

As discussed with @Ralith on IRC, I don't think we need to include these headers just for backwards compatibility. They were removed from vulkan-loader upstream some time ago, it's up to the people using it to read the release notes that the headers aren't included anymore.