{
  inputs = {
    # nixpkgs.url = github:nixos/nixpkgs?ref=1a8754caf8eb8831b904daaf34b2ee737053b383; # commit for the 13.0.1 LLVM bump
    nixpkgs.url = github:nixos/nixpkgs/nixpkgs-unstable; # LLVM 13 is broken on Darwin on 21.11; using < instead of ^ so we get caching
    flake-utils.url = github:numtide/flake-utils;
  };

  # The issue only affects Darwin. Both because symbol rexport is only a thing
  # on mach-o platforms
  # (https://github.com/llvm/llvm-project/blob/4f13b999297140486b2faa1b5d8d7c768fb40dfb/libcxx/src/CMakeLists.txt#L202-L215)
  # and because `-lc++abi` is always added to the cc wrapper for Linux:
  # https://github.com/NixOS/nixpkgs/blob/a785ec661fadba2ded58467f951b51c34631c269/pkgs/build-support/cc-wrapper/default.nix#L382
  outputs = { self, nixpkgs, flake-utils }: flake-utils.lib.eachSystem [ "aarch64-darwin" "x86_64-darwin" ] (system:
    let
      normal = import nixpkgs { inherit system; };
      imp = func: import nixpkgs { inherit system; config.replaceStdenv = { pkgs }: (func pkgs).libcxxStdenv; };
      l_11 = imp (n: n.llvmPackages_11);
      l_12 = imp (n: n.llvmPackages_12);
      l_13 = imp (n: n.llvmPackages_13);
      l_13' = import nixpkgs {
        inherit system;
        # config.replaceStdenv = { pkgs }: pkgs.llvmPackages_13.libcxxStdenv.overrideAttrs (old: {
        #   postFixup = old.postFixup + ''
        #     echo "-lc++abi" >> $out/nix-support/libcxx-ldflags
        #   '';
        # });
        config.replaceStdenv = { pkgs }:
          let
            clang' = pkgs.llvmPackages_13.libcxxClang.overrideAttrs (old: {
              # We _should_ use an overlay or something similar here but they allegedly don't interact well with `replaceStdenv`.
              #
              # We're essentially adding this: https://github.com/NixOS/nixpkgs/blob/3491c5ea290bca5437845b6348919fcb23950af9/pkgs/build-support/cc-wrapper/default.nix#L382
              postFixup = old.postFixup + ''
                echo "-lc++abi" >> $out/nix-support/libcxx-ldflags
              '';
            });

            # https://github.com/NixOS/nixpkgs/blob/904ed45698338365f086c22ab5af167adf8bee9a/pkgs/development/compilers/llvm/13/default.nix#L241
            stdenv' = pkgs.overrideCC pkgs.stdenv clang';
          in
            stdenv';
      };

      cmd = ''clang++ -xc++ - <<<"int main() { throw 4; return 0; }" -v'';
      test = np: np.runCommandCC "test-cxx" {} ''
        ${cmd} -o $out
      '';
      hook = ''
        cd "$(mktemp -d)"
        libcxx_dir="$(${cmd} -o out -Wl,-v |& tee /dev/stderr | grep -P '\t/nix/store/.*-libcxx-.*/lib' | tail -1)"
        libcxx=$(echo "$libcxx_dir/libc++.dylib" | xargs)

        echo -e "\nlibcxx: $libcxx"
        echo "contains:"
        ${normal.llvmPackages.llvm}/bin/llvm-nm -C "$libcxx" | grep __cxa_allocate_exception
      '';
    in {

    # `nix flake check` shows the error
    checks.l11 = test l_11; # Works fine
    checks.l12 = test l_12; # Fails
    checks.l13 = test l_13; # Fails
    checks.l13' = test l_13'; # A workaround

    devShells = {
      llvm11 = l_11.mkShell { shellHook = hook; };
      llvm12 = l_12.mkShell { shellHook = hook; };
      llvm13 = l_13.mkShell { shellHook = hook; };
    };
  });
}