by priority and version install. That is, if there are multiple
packages with the same name, then pick the package with the highest
priority, and only use the version if there are multiple packages
with the same priority.
This makes it possible to mark specific versions/variant in Nixpkgs
more or less desirable than others. A typical example would be a
beta version of some package (e.g., "gcc-4.2.0rc1") which should not
be installed even though it is the highest version, except when it
is explicitly selected (e.g., "nix-env -i gcc-4.2.0rc1").
* Idem for nix-env -u, only the semantics are a bit trickier since we
also need to take into account the priority of the currently
installed package (we never upgrade to a lower priority, unless
--always is given).
evaluator. This was important because the NixOS expressions started
to hit 2 MB default stack size on Linux.
GCC is really dumb about stack space: it just adds up all the local
variables and temporaries of every scope into one huge stack frame.
This is really bad for deeply recursive functions. For instance,
every `throw Error(format("error message"))' causes a format object
of a few hundred bytes to be allocated on the stack. As a result,
every recursive call to evalExpr2() consumed 4680 bytes. By
splitting evalExpr2() and by moving the exception-throwing code out
of the main functions, evalExpr2() now only consumes 40 bytes.
Similar for evalExpr().
attribute) about installed packages in user environments. Thus, an
operation like `nix-env -q --description' shows useful information
not only on available packages but also on installed packages.
* nix-env now passes the entire manifest as an argument to the Nix
expression of the user environment builder (not just a list of
paths), so that in particular the user environment builder has
access to the meta attributes.
* New operation `--set-flag' in nix-env to change meta info of
installed packages. This will be useful to pass per-package
policies to the user environment builder (e.g., how to resolve
collision or whether to disable a package (NIX-80)) or upgrade
policies in nix-env (e.g., that a package should be "masked", that
is, left untouched by upgrade actions). Example:
$ nix-env --set-flag enabled false ghc-6.4
computing the store path (NIX-77). This is an important security
property in multi-user Nix stores.
Note that this changes the store paths of derivations (since the
derivation aterms are added using addTextToStore), but not most
outputs (unless they use builtins.toFile).
* `sub' to subtract two numbers.
* `stringLength' to get the length of a string.
* `substring' to get a substring of a string. These should be enough
to allow most string operations to be expressed.
<derivation outPath=... drvPath=...> attrs </derivation>. Only emit
the attributes of any specific derivation only. This prevents
exponententially large XML output due to the absense of sharing.
from a source directory. All files for which a predicate function
returns true are copied to the store. Typical example is to leave
out the .svn directory:
stdenv.mkDerivation {
...
src = builtins.filterSource
(path: baseNameOf (toString path) != ".svn")
./source-dir;
# as opposed to
# src = ./source-dir;
}
This is important because the .svn directory influences the hash in
a rather unpredictable and variable way.
containing functions that operate on the Nix store. One
implementation is LocalStore, which operates on the Nix store
directly. The next step, to enable secure multi-user Nix, is to
create a different implementation RemoteStore that talks to a
privileged daemon process that uses LocalStore to perform the actual
operations.
concatenation and string coercion. This was a big mess (see
e.g. NIX-67). Contexts are now folded into strings, so that they
don't cause evaluation errors when they're not expected. The
semantics of paths has been clarified (see nixexpr-ast.def).
toString() and coerceToString() have been merged.
Semantic change: paths are now copied to the store when they're in a
concatenation (and in most other situations - that's the
formalisation of the meaning of a path). So
"foo " + ./bla
evaluates to "foo /nix/store/hash...-bla", not "foo
/path/to/current-dir/bla". This prevents accidental impurities, and
is more consistent with the treatment of derivation outputs, e.g.,
`"foo " + bla' where `bla' is a derivation. (Here `bla' would be
replaced by the output path of `bla'.)
side should be a path, I guess.
* Handle paths that are in the store but not direct children of the
store directory.
* Ugh, hack to prevent double context wrapping.
