write ‘attrs ? a.b’ to test whether ‘attrs’ has an attribute ‘a’
containing an attribute ‘b’. This is more convenient than ‘attrs ?
a && attrs.a ? b’.
Slight change in the semantics: it's no longer an error if the
left-hand side of ‘?’ is not an attribute set. In that case it just
returns false. So, ‘null ? foo’ no longer throws an error.
a pointer to a Value, rather than the Value directly. This improves
the effectiveness of garbage collection a lot: if the Value is
stored inside the set directly, then any live pointer to the Value
causes all other attributes in the set to be live as well.
errors with position info.
* For all positions, use the position of the first character of the
first token, rather than the last character of the first token plus
one.
use site, allowing environments to be stores as vectors of values
rather than maps. This should speed up evaluation and reduce the
number of allocations.
efficiently. The symbol table ensures that there is only one copy
of each symbol, thus allowing symbols to be compared efficiently
using a pointer equality test.
allowed. So `name1@name2', `{attrs1}@{attrs2}' and so on are now no
longer legal. This is no big loss because they were not useful
anyway.
This also changes the output of builtins.toXML for @-patterns
slightly.
shorthand for {x = {y = {z = ...;};};}. This is especially useful
for NixOS configuration files, e.g.
{
services = {
sshd = {
enable = true;
port = 2022;
};
};
}
can now be written as
{
services.sshd.enable = true;
services.sshd.port = 2022;
}
However, it is currently not permitted to write
{
services.sshd = {enable = true;};
services.sshd.port = 2022;
}
as this is considered a duplicate definition of `services.sshd'.
in attribute set pattern matches. This allows defining a function
that takes *at least* the listed attributes, while ignoring
additional attributes. For instance,
{stdenv, fetchurl, fuse, ...}:
stdenv.mkDerivation {
...
};
defines a function that requires an attribute set that contains the
specified attributes but ignores others. The main advantage is that
we can then write in all-packages.nix
aefs = import ../bla/aefs pkgs;
instead of
aefs = import ../bla/aefs {
inherit stdenv fetchurl fuse;
};
This saves a lot of typing (not to mention not having to update
all-packages.nix with purely mechanical changes). It saves as much
typing as the "args: with args;" style, but has the advantage that
the function arguments are properly declared (not implicit in what
the body of the "with" uses).
functions that take a single argument (plain lambdas) into one AST
node (Function) that contains a Pattern node describing the
arguments. Current patterns are single lazy arguments (VarPat) and
matching against an attribute set (AttrsPat).
This refactoring allows other kinds of patterns to be added easily,
such as Haskell-style @-patterns, or list pattern matching.
undefined variables by definition. This matters for the
implementation of "with", which does a call to checkVarDefs to see
if the body of the with has no undefined variables. (It can't be
checked at parse time because you don't know which variables are in
the "with" attribute set.) If we check closed terms, then we check
not just the with body but also the substituted terms, which are
typically very large. This is the cause of the poor nix-env
performance on Nixpkgs lately. It didn't happen earlier because
"with" wasn't used very often in the past.
This fix improves nix-env performance roughly 60x on current Nixpkgs.
nix-env -qa is down from 29.3s to 0.5s on my laptop, and nix-env -qa
--out-path is down from 229s to 3.39s. Not bad for a 1-line fix :-)
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
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'.)
argument has a valid value, i.e., is in a certain domain. E.g.,
{ foo : [true false]
, bar : ["a" "b" "c"]
}: ...
This previously could be done using assertions, but domain checks
will allow the buildfarm to automatically extract the configuration
space from functions.
(closed(closed(closed(...)))) since this reduces performance by
producing bigger terms and killing caching (which incidentally also
prevents useful infinite recursion detection).
`derivations.cc', etc.
* Store the SHA-256 content hash of store paths in the database after
they have been built/added. This is so that we can check whether
the store has been messed with (a la `rpm --verify').
* When registering path validity, verify that the closure property
holds.
Eelco Dolstra