Zig fails to get the include paths on NixOS Unstable

[sagehane]

Problem:

NixOS fails to detect system header locations on Unstable, accompanied by the following error:

warning: Unrecognized C flag from NIX_CFLAGS_COMPILE: -frandom-seed=<some 10 digit string>

Tested on:

$ nixos-version
21.05pre275822.916ee862e87 (Okapi)

How to reproduce:

1. Prepare a Zig project that interfaces with C code, such as the the raylib example code on the main page.
2. Use nix-shell to install the required dependencies (raylib in this case).
3. Attempt to compile the file (zig build-exe cimport.zig -lc -lraylib as per the code comment).

The cause:

NixOS/nixpkgs#102251 added -frandom-seed as one of the flags of NIX_CFLAGS_COMPILE.

An example of what happens after running nix-shell -p raylib:

$ echo $NIX_CFLAGS_COMPILE
-frandom-seed=k1in0vqnyx -isystem /nix/store/ndbz36pb6rl0n2582n6598az61bsa7pl-raylib-3.5.0/include -isystem /nix/store/ndbz36pb6rl0n2582n6598az61bsa7pl-raylib-3.5.0/include

Since Zig doesn't expect this, it breaks out of the loop described here and doesn't properly add the header paths.

Possible Solutions:

Zig should adds support for passing -frandom-seed. Should be the ideal fix? Should just be about working on that loop mentioned above.

Also, idk if Zig is supposed to have feature parity with Clang, but frandom-seed seems to be mentioned here.

---

According to NixOS/nixpkgs#109033, NixOS currently lacks a way to disable this flag from being added.

As such, for people who just want to "ignore" the problem, they can add something like this to the shell.nix file:

  # This is a workaround that needs to be revised
  shellHook = ''
    NIX_CFLAGS_COMPILE="$(echo "$NIX_CFLAGS_COMPILE" | sed -e "s/-frandom-seed=[^-]*//")"
  '';

[will]

I'm having a similar issue while building a zig 0.13 project inside of the devshell provided by github:Cloudef/zig2nix on macos. zig build worked fine until I added exe.linkSystemLibrary("libgit2"); to the build.zig file. Then it started erroring with

error: warning: Unrecognized C flag from NIX_CFLAGS_COMPILE: -isysroot
warning: Unrecognized C flag from NIX_CFLAGS_COMPILE: /nix/store/7n8zp0cpbnf1rf7d3dc7gi0x43iadqn3-sdkroot-11.0/MacOSX11.0.sdk

and the value for that env var for me is

❯ echo $NIX_CFLAGS_COMPILE
 -frandom-seed=maaa31cchk -isysroot /nix/store/7n8zp0cpbnf1rf7d3dc7gi0x43iadqn3-sdkroot-11.0/MacOSX11.0.sdk

[nektro]

that's #18998. also make sure to check out Communitys