A few packaging nits, coming from Nixpkgs/NixOS

Hi, you can see how we currently package this in https://github.com/nixos/nixpkgs/blob/master/pkgs/development/libraries/wasilibc/default.nix.

There are no imminent problems (the situation is less fraught than I thought) but I few things I think could be improved.

Install dirs

We generally like to have "mutliple outputs" for our libraries. That means we install to something like /nix/store/random-foo/lib, /nix/store/random-bar/include, etc. notice the random-{foo,bar} are not the same.

We generally use the "GNU-style: install dirs" to achieve this. C.f.

• Autoconf: https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Installation-Directory-Variables.html
• CMake: https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html
• Meson: https://mesonbuild.com/Builtin-options.html#directories

You have
https://github.com/WebAssembly/wasi-libc/blob/079adff840032c3455eb1cb34dc9ceaa0b2bfc0c/Makefile#L8
and
https://github.com/WebAssembly/wasi-libc/blob/079adff840032c3455eb1cb34dc9ceaa0b2bfc0c/Makefile#L246-L248

for this. It would be nice to make the second ones ?= too, and relax the assumption that that they share a parent directory.

That list bit part means getting rid of other uses of SYSROOT (it can just be a way to default the defaults for those three, so e.g.:

Tool env vars

You use WASM_*, e.g. WASM_CC. The convention however is that CC, LD, etc. are the tools for the current package, for the current platform, one is installing too. Conversely, if one needed to build e.g. some temporary codegen tool (a common use case, but not on in wasi libc to my knowledge), one would use CC_FOR_BUILD, LD_FOR_BUILD etc.

This means the WASM_ prefix is not needed.

I would suggest just getting rid of them. The wrapper wasi-sdk already does recursive make:
https://github.com/WebAssembly/wasi-sdk/blob/20c5bcd791e22895ea1c9721c9bd88081e3ed1f6/Makefile#L92-L96

build/wasi-libc.BUILT: build/llvm.BUILT
	$(MAKE) -C $(ROOT_DIR)/src/wasi-libc \
		WASM_CC=$(BUILD_PREFIX)/bin/clang \
		...

This makes scoped variables easy, so you can just do

build/wasi-libc.BUILT: build/llvm.BUILT
	$(MAKE) -C $(ROOT_DIR)/src/wasi-libc \
		CC=$(BUILD_PREFIX)/bin/clang \
		...

instead, and not worry about clashes with any "global" CC.

Start with the referenced Makefile assignments at lines 8 and 246-248, then inspect other SYSROOT and WASM_* uses. Review the wasi-sdk Makefile rule that invokes wasi-libc and the nixpkgs package definition. Done means install directories can be set independently and the tool environment follows the proposed convention without breaking the wrapper.