Our use of boost::coroutine2 depends on -lboost_context,
which in turn depends on `-lboost_thread`, which in turn depends
on `-lboost_system`.
I suspect that this builds on nix only because of low-level hacks
like NIX_LDFLAGS.
This commit passes the proper linker flags, thus fixing bootstrap
builds on non-nix distributions like Ubuntu 16.04.
With these changes, I can build Nix on Ubuntu 16.04 using:
./bootstrap.sh
./configure --prefix=$HOME/editline-prefix \
--disable-doc-gen \
CXX=g++-7 \
--with-boost=$HOME/boost-prefix \
EDITLINE_CFLAGS=-I$HOME/editline-prefix/include \
EDITLINE_LIBS=-leditline \
LDFLAGS=-L$HOME/editline-prefix/lib
make
where
* g++-7 comes from gcc-7 from
https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test,
* editline 1.14 from https://github.com/troglobit/editline/releases/tag/1.14.0
was installed into `$HOME/editline-prefix`
(because Ubuntu 16.04's `editline` is too old to have the function nix uses),
* boost 1.66 from
https://www.boost.org/doc/libs/1_66_0/more/getting_started/unix-variants.html
was installed into $HOME/boost-prefix (because Ubuntu 16.04 only has 1.58)
'updateCV.notify_one()' does nothing if the update thread is not
waiting for updateCV (in particular this happens when it is sleeping
on quitCV). So also set a variable to ensure that the update isn't
lost.
This exploits the hermetic nature of flake evaluation to speed up
repeated evaluations of a flake output attribute.
For example (doing 'nix build' on an already present package):
$ time nix build nixpkgs:firefox
real 0m1.497s
user 0m1.160s
sys 0m0.139s
$ time nix build nixpkgs:firefox
real 0m0.052s
user 0m0.038s
sys 0m0.007s
The cache is ~/.cache/nix/eval-cache-v1.sqlite, which has entries like
INSERT INTO Attributes VALUES(
X'92a907d4efe933af2a46959b082cdff176aa5bfeb47a98fabd234809a67ab195',
'packages.firefox',
1,
'/nix/store/pbalzf8x19hckr8cwdv62rd6g0lqgc38-firefox-67.0.drv /nix/store/g6q0gx0v6xvdnizp8lrcw7c4gdkzana0-firefox-67.0 out');
where the hash 92a9... is a fingerprint over the flake store path and
the contents of the lockfile. Because flakes are evaluated in pure
mode, this uniquely identifies the evaluation result.
As long as the flake input is locked, it is now only fetched when it
is evaluated (e.g. "nixpkgs" is fetched when
"inputs.nixpkgs.<something>" is evaluated).
This required adding an "id" attribute to the members of "inputs" in
lockfiles, e.g.
"inputs": {
"nixpkgs/release-19.03": {
"id": "nixpkgs",
"inputs": {},
"narHash": "sha256-eYtxncIMFVmOHaHBtTdPGcs/AnJqKqA6tHCm0UmPYQU=",
"nonFlakeInputs": {},
"uri": "github:edolstra/nixpkgs/e9d5882bb861dc48f8d46960e7c820efdbe8f9c1"
}
}
because the flake ID needs to be known beforehand to construct the
"inputs" attrset.
Fixes#2913.
This is like 'nix run', except that the command to execute is defined
in a flake output, e.g.
defaultApp = {
type = "app";
program = "${packages.blender_2_80}/bin/blender";
};
Thus you can do
$ nix app blender-bin
to start Blender from the 'blender-bin' flake.
In the future, we can extend this with sandboxing. (For example we
would want to be able to specify that Blender should not have network
access by default and should only have access to certain paths in the
user's home directory.)
