So for instance "nix copy --to ... nixpkgs.hello" will build
nixpkgs.hello first. It's debatable whether this is a good idea. It
seems desirable for commands like "nix copy" but maybe not for
commands like "nix path-info".
Thus
$ nix build -f foo.nix
will build foo.nix.
And
$ nix build
will build default.nix. However, this may not be a good idea because
it's kind of inconsistent, given that "nix build foo" will build the
"foo" attribute from the default installation source (i.e. the
synthesis of $NIX_PATH), rather than ./default.nix. So I may revert
this.
This allows commands like 'nix path-info', 'nix copy', 'nix verify'
etc. to work on arbitrary installables. E.g. to copy geeqie to a
binary cache:
$ nix copy -r --to file:///tmp/binary-cache nixpkgs.geeqie
Or to get the closure size of thunderbird:
$ nix path-info -S nixpkgs.thunderbird
In particular, this disallows attribute names containing dots or
starting with dots. Hydra already disallowed these. This affects the
following packages in Nixpkgs master:
2048-in-terminal
2bwm
389-ds-base
90secondportraits
lispPackages.3bmd
lispPackages.hu.dwim.asdf
lispPackages.hu.dwim.def
Closes#1342.
The typical use is to inherit Config and add Setting<T> members:
class MyClass : private Config
{
Setting<int> foo{this, 123, "foo", "the number of foos to use"};
Setting<std::string> bar{this, "blabla", "bar", "the name of the bar"};
MyClass() : Config(readConfigFile("/etc/my-app.conf"))
{
std::cout << foo << "\n"; // will print 123 unless overriden
}
};
Currently, this is used by Store and its subclasses for store
parameters. You now get a warning if you specify a non-existant store
parameter in a store URI.
This provides a significant speedup, e.g. 64 s -> 12 s for
nix-build --dry-run -I nixpkgs=channel:nixos-16.03 '<nixpkgs/nixos/tests/misc.nix>' -A test
on a cold local and CloudFront cache.
The alternative is to use lots of concurrent daemon connections but
that seems wasteful.
This is useless because the client also caches path info, and can
cause problems for long-running clients like hydra-queue-runner
(i.e. it may return cached info about paths that have been
garbage-collected).
