Test Clang integration

[Synthetica9]

There is some special code to support Clang (

EPNix/pkgs/epnix/epics-base/default.nix

Lines 47 to 93 in fefa2bf

	build_config_site =
	generateConf
	(with buildPackages.stdenv;
	{
	CC = "${cc.targetPrefix}cc";
	CCC = "${cc.targetPrefix}c++";
	CXX = "${cc.targetPrefix}c++";
	AR = "${cc.bintools.targetPrefix}ar";
	LD = "${cc.bintools.targetPrefix}ld";
	RANLIB = "${cc.bintools.targetPrefix}ranlib";
	ARFLAGS = "rc";
	}
	// optionalAttrs cc.isClang {
	GNU = "NO";
	CMPLR_CLASS = "clang";
	});
	# "host" as in Nix terminology (the machine which will run the generated code)
	host_config_site =
	generateConf
	(with stdenv;
	{
	CC = "${cc.targetPrefix}cc";
	CCC =
	if stdenv.cc.isClang
	then "${cc.targetPrefix}clang++"
	else "${cc.targetPrefix}c++";
	CXX =
	if stdenv.cc.isClang
	then "${cc.targetPrefix}clang++"
	else "${cc.targetPrefix}c++";
	AR = "${cc.bintools.targetPrefix}ar";
	LD = "${cc.bintools.targetPrefix}ld";
	RANLIB = "${cc.bintools.targetPrefix}ranlib";
	ARFLAGS = "rc";
	COMMANDLINE_LIBRARY = "READLINE_NCURSES";
	}
	// optionalAttrs cc.isClang {
	GNU = "NO";
	CMPLR_CLASS = "clang";
	});

)

I tried exercising this by overriding stdenv to clangStdenv, but that mixes gcc and clang...

The question here is two-fold

1. Is this still supported, or has this bit-rotted in the mean time? If this is still supported, how should I access this?
2. Should we test this somehow? Seems prudent to at least build the epics-base package with clang if we have specific code to support this

[minijackson]

Is this still supported, or has this bit-rotted in the mean time? If this is still supported, how should I access this?

I tested it a while time ago, to stop clang-tidy / clangd from bothering me by trying to include the gcc-specific header files.

Should we test this somehow? Seems prudent to at least build the epics-base package with clang if we have specific code to support this

I'm in favor of testing this. What's your usecase? Is this to prepare for macOS support?

I've managed to build epics-base with clang in the REPL like this:

pkgs = import <nixpkgs> { overlays = [epnix.overlays.default]; }
pkgs.epnix.epics-base.override {
  stdenv = pkgs.clangStdenv;
  buildPackages = pkgs.buildPackages // { stdenv = pkgs.buildPackages.clangStdenv; };
  mkEpicsPackage = pkgs.mkEpicsPackage.override {
    stdenv = pkgs.clangStdenv;
    buildPackages = pkgs.buildPackages // { stdenv = pkgs.buildPackages.clangStdenv; };
  };
}

It's way too convoluted for my taste. Here's what I think could make it simpler:

• retire mkEpicsPackage and use setup hooks instead
• see if we it's possible to use package splicing instead of buildPackages, so we don't need to specify clangStdenv twice.

[Synthetica9]

What's your usecase? Is this to prepare for macOS support?

I had no specific use-case, I wanted to try a different compiler to diagnose the hardening issue in solved in #67, but maybe OpenBSD down the line. I just ran into the Clang-specific code that was not exercised anywhere