Comment obtenir de nouvelles versions de Nixpkgs stdenv pour définir NIX_CFLAGS/NIX_LDFLAGS pour 'libav'?

Question

Le stdenv des versions plus récentes de Nixpkgs ne parvient pas à définir NIX_CFLAGS/NIX_LDFLAGS pour le package libav, qui a fonctionné dans les anciennes versions. Que fais-je wong?

Le script suivant illustre le problème. Elle gère plusieurs construit avec buildInputs = [ libav ]; en utilisant différentes versions du STDENV et imprime les valeurs respectives de NIX_LDFLAGS et NIX_CFLAGS_COMPILE:

# Eval in shell 
nix-build --no-out-link - <<'EOF' 
let 
pkgs = (import <nixpkgs> {}); 
fetchNixPkgs = { rev, sha256 }: 
    pkgs.fetchFromGitHub rec { 
    inherit sha256 rev; 
    owner = "NixOS"; 
    repo = "nixpkgs-channels"; 
    name = "adhoc-nixpkgs"; 
    }; 
loadNixPkgs = args: import (fetchNixPkgs args) {}; 
pkgsVersions = { 
    # Aug 21, 2016 
    # This one works correctly: CFLAGS/LDFLAGS includes references to libav 
    working = loadNixPkgs { 
    rev = "5120af001f2bb163b58c41c84b11a0c136a207fe"; 
    sha256 = "18h0aww5m17fip90zld8yqbz9f76ax5ws13krqgrccghn9i9hjlj"; 
    }; 
    # Jul 5, 2017 
    # The latest version: libav isn't included in CFLAGS/LDFLAGS 
    # This issue is also present in older versions 
    current = loadNixPkgs { 
    rev = "c2e3f7b687660fed7e0056ef1300a2efdfca6e4e"; 
    sha256 = "0yp34xr8nkagn75d5sc0igynipvvr3mjcmz52scqd9isd7nmmfjs"; 
    }; 
    # Nov 11, 2016. An older version with the same issue 
    older = loadNixPkgs { 
    rev = "cf57b79fb1b4d1c261a1b27eaed75aefe99bd498"; 
    sha256 = "1m5yjfnjckl8qjz2kxjj7zy074jdmn4r1csqgmf65024hlhqdz8r"; 
    }; 
}; 
libav = pkgsVersions.current.libav.dev; 
# libav = pkgsVersions.working.libav; # This one works, too 
showEnv = pkgsVersion: 
    let 
    pkgs = pkgsVersions.${pkgsVersion}; 
    in 
    pkgs.runCommand "test-env" { inherit pkgsVersion; buildInputs = [ libav ]; } '' 
    mkdir -p $out 
    echo 
    echo "============ Build environment for pkgs version '$pkgsVersion' ============" 
    echo NIX_LDFLAGS=$NIX_LDFLAGS 
    echo NIX_CFLAGS_COMPILE=$NIX_CFLAGS_COMPILE 
    echo 
    ''; 
in 
map showEnv (builtins.attrNames pkgsVersions) 
EOF 

Sortie:

building path(s) ‘/nix/store/32jvx9cqafs54jcd0fbcdq6y93wyg8nm-test-env’ 

(Commentary: That's how it should look like) 
↓ 
============ Build environment for pkgs version 'working' ============ 
NIX_LDFLAGS=-rpath /nix/store/32jvx9cqafs54jcd0fbcdq6y93wyg8nm-test-env/lib64 -rpath /nix/store/32jvx9cqafs54jcd0fbcdq6y93wyg8nm-test-env/lib -L/nix/store/b4viv3w9hzshp1i6zld219s3aszqdb4n-libav-11.9-dev/lib -L/nix/store/9li7l66zhd6lwhh34vbkx7zydk9cw3sz-libav-11.9/lib 
NIX_CFLAGS_COMPILE= -isystem /nix/store/b4viv3w9hzshp1i6zld219s3aszqdb4n-libav-11.9-dev/include 


building path(s) ‘/nix/store/j75z46xvfcl9512pi1rmahmslmlzk4ks-test-env’ 

============ Build environment for pkgs version 'current' ============ 
NIX_LDFLAGS=-rpath /nix/store/j75z46xvfcl9512pi1rmahmslmlzk4ks-test-env/lib64 -rpath /nix/store/j75z46xvfcl9512pi1rmahmslmlzk4ks-test-env/lib 
NIX_CFLAGS_COMPILE= 

building path(s) ‘/nix/store/1gic4s1jdv36pjkn5akrn98y215ll2al-test-env’ 

============ Build environment for pkgs version 'older' ============ 
NIX_LDFLAGS=-rpath /nix/store/1gic4s1jdv36pjkn5akrn98y215ll2al-test-env/lib64 -rpath /nix/store/1gic4s1jdv36pjkn5akrn98y215ll2al-test-env/lib 
NIX_CFLAGS_COMPILE= 

Answer 1

La solution est d'ajouter gcc-buildInputs ou à utiliser runCommandCC au lieu de runCommand:

nix-build --no-out-link - <<'EOF' 
with (import <nixpkgs> {}); 
runCommand "test-env" { buildInputs = [ gcc libav ]; } '' 
    mkdir -p $out 
    echo NIX_LDFLAGS=$NIX_LDFLAGS 
    echo NIX_CFLAGS_COMPILE=$NIX_CFLAGS_COMPILE 
'' 
EOF