[Nix-dev] nix-build building (too much) stuff?

[Tobias Hunger]

Hello!

I am currently trying to make the perl-5.10 nix package know the location 
where vendor stuff should be installed to unbreak the perl code e.g.
contained in the dpkg derivation we have.

So I ran nix-build -K /etc/nixos/nixpkgs -A perl to test this.

With an unmodified default.nix that works fine:
/etc/nixos/nixpkgs/pkgs/development/interpreters/perl-5.10]# nix-build -K 
/etc/nixos/nixpkgs -A perl            
/nix/store/yqr853y8m593b9kq4a58gj19f3zw6grv-perl-5.10.1

Once I add a single space into one of the parameters passed when configuring 
perl I get this instead:

/etc/nixos/nixpkgs/pkgs/development/interpreters/perl-5.10]# nix-build -K 
/etc/nixos/nixpkgs -A perl            
these derivations will be built:
  /nix/store/090c3fnffv4ys8a0jdvfjr3l2bsdk2b1-ed-1.4.drv
  /nix/store/19aym1j8l4p74wflm4qi21w8b0fa9p01-gettext-0.18.1.1.drv
  /nix/store/1c5zcbm7fdh4bd6bfl31ak4vfq6vlgm4-gnugrep-2.7.drv
  /nix/store/1nxwa72d99w6cy8i50svpmgz8ja74a2q-patch-2.6.1.drv
  /nix/store/2iyzvbzd2fp7wvpl9d7n02zrw4m5gl5w-gnumake-3.82.drv
  /nix/store/403afjypxi6pj4djkbjlk8zrr1hh9a8q-ppl-0.10.2.drv
  /nix/store/46w94g62r65fwkqv8q74fr9zjsxiq7hv-xz-5.0.0.drv
  /nix/store/49733snbby663hhlfi80l7x7qlwccmld-gzip-1.4.drv
  /nix/store/4gpkfdgc4vcabra9n95412vp506sycjd-gnused-4.2.1.drv
  /nix/store/535bxg65srnn5f49mnmvhwdrfvbxiwzb-libelf-0.8.13.drv
  /nix/store/65cb6kakwpjdbq237ipasj2lcbgsw82l-cloog-ppl-0.15.9.drv
  /nix/store/6sc6yjsxp3wfhxjb967wpy8chyd799zg-gcc-wrapper-4.5.1.drv
  /nix/store/7wk646hki00x7imb90rmffj2fwf7ccjn-gmp-4.3.2.drv
  /nix/store/811qfz42qvprpjg6drsv7mfhk99ppvsh-stdenv-linux-boot.drv
  /nix/store/9n3lppm342rg7jjlca5k7jzhs9aqq94a-bison-2.4.3.drv
  /nix/store/a9yz6g4lm6p7awnzcb60535ac16xn502-gnutar-1.25.drv
  /nix/store/agdpgbcp7nwxsh2gp116gnkjb5sddhm5-coreutils-8.7.drv
  /nix/store/aj3skf911y0fk205l537jvsj22ijb048-gnum4-1.4.15.drv
  /nix/store/ap6mpzd3pzkgm643cdzkifd4vpdsqma9-perl-5.10.1.drv
  /nix/store/b4awy59a89hpm95h6r2yvdkm2yij9pns-zlib-1.2.5.drv
  /nix/store/bblz3sfnghmkqk0d5hi13jbaf9vmc3h6-stdenv-linux-boot.drv
  /nix/store/ccgx8cqskxbfy19ykqsl7ypd25wqgg2h-findutils-4.4.2.drv
  /nix/store/cn6cyzmli8icfi1kaycn119ha8i3iawn-replace-2.24.drv
  /nix/store/fmzl9pg264pa23vclvm9xm21n0mgm3rl-gmp-4.3.2.drv
  /nix/store/gq7q6q540n2g4bab7djrk6lial4zf6wa-gettext-0.18.1.1.drv
  /nix/store/i3dr46xml2nph7djw8vi45nnr43a1vxc-readline-6.1.drv
  /nix/store/j8ipspy7jplip0nydvfqj8b4bak47cmp-patchelf-0.5.drv
  /nix/store/ka9m6gcwj7kwzmvzcc0fh66cbj14y27h-acl-2.2.49.drv
  /nix/store/kc50mwbzr0f5ng679j28fvl3qlggb30p-gcc-4.5.1.drv
  /nix/store/kjhy09a3kmzx0yr1p5crcj5fq22a9878-perl-5.10.1.drv
  /nix/store/l4fic6ksh1j3a8mmbvqv60xxr6m1rz5d-libsigsegv-2.8.drv
  /nix/store/lbn13p54lvrm2h9fbk0qz1jxc2rijs27-bzip2-1.0.5.drv
  /nix/store/ldvac732i58gk48p5xi2b654m5is1d7b-which-2.20.drv
  /nix/store/m2wa36jg1jd1ywziyhp761l2vqxfjg9z-gcc-wrapper-4.5.1.drv
  /nix/store/mfrrq8bsa03z0qyb2m4x1p977pa4lwqg-gnum4-1.4.15.drv
  /nix/store/n49glpdlv6dnsg10asib3dgvy39j3wv8-pcre-8.10.drv
  /nix/store/p4i7jlk4zk08p0znrk2n6fqzcmjn63qj-bash-4.1-p2.drv
  /nix/store/pf1xr8jcz5bs0jr9qys5ipiyvbwc1yaa-texinfo-4.13a.drv
  /nix/store/pwvqgzml262019xczpbizj3xwfxlmycn-stdenv-linux.drv
  /nix/store/q05k15m19jwdgbk9xn2sc4092qyx0h8h-perl-5.10.1.drv
  /nix/store/r9kfr1ccd30p494k7vzkvjbpgpp9kfs4-attr-2.4.44.drv
  /nix/store/rawjh01f0kzdx2n5c40h0l50yzq3d33g-glibc-2.12.2.drv
  /nix/store/rjqyc15g83pk5g6q5wfcx8fqq5s8ympr-diffutils-3.0.drv
  /nix/store/s6dfcsrfpkp9hhd40cgq0296gqcnq5pv-linux-headers-2.6.32.16.drv
  /nix/store/va1n599g7y67a653acrmca5gm3zgmbny-ncurses-5.7.drv
  /nix/store/vnmbzsldsib41yk1w550s0qxyj48g8js-gmp-4.3.2.drv
  /nix/store/vppsqqc52d7v7s1hblx9p080zvdp43zk-mpfr-3.0.0.drv
  /nix/store/wqs2jqxci2dg39b0irjxas3a9ml27fxp-mpc-0.8.2.drv
  /nix/store/xagh1j9q0lzqzwxvj88mspjz023xrya5-bootstrap-gcc-wrapper.drv
  /nix/store/ywqhsh063zyrnj7c88sm2d7n9n8rznnv-gawk-3.1.8.drv
  /nix/store/zkhwn36qkqxzzsl6219q6vlpbbbdm71b-binutils-2.21.drv
building path(s) `/nix/store/n2cv7zqjslxiq94c9hja9qdl4x5bapz8-perl-5.10.1'

Could somebody please explain why that happens? How can I find out why 
something gets rebuild? Is there a way to rebuild perl only?

Best Regards,
Tobias