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Nix search path lookups like <nixpkgs> are now desugared to ‘findFile
nixPath <nixpkgs>’, where ‘findFile’ is a new primop. Thus you can
override the search path simply by saying
let
nixPath = [ { prefix = "nixpkgs"; path = "/my-nixpkgs"; } ];
in ... <nixpkgs> ...
In conjunction with ‘scopedImport’ (commit
c273c15cb13bb86420dda1e5341a4e19517532b5), the Nix search path can be
propagated across imports, e.g.
let
overrides = {
nixPath = [ ... ] ++ builtins.nixPath;
import = fn: scopedImport overrides fn;
scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
builtins = builtins // overrides;
};
in scopedImport overrides ./nixos
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Also fixes #261.
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‘scopedImport’ works like ‘import’, except that it takes a set of
attributes to be added to the lexical scope of the expression,
essentially extending or overriding the builtin variables. For
instance, the expression
scopedImport { x = 1; } ./foo.nix
where foo.nix contains ‘x’, will evaluate to 1.
This has a few applications:
* It allows getting rid of function argument specifications in package
expressions. For instance, a package expression like:
{ stdenv, fetchurl, libfoo }:
stdenv.mkDerivation { ... buildInputs = [ libfoo ]; }
can now we written as just
stdenv.mkDerivation { ... buildInputs = [ libfoo ]; }
and imported in all-packages.nix as:
bar = scopedImport pkgs ./bar.nix;
So whereas we once had dependencies listed in three places
(buildInputs, the function, and the call site), they now only need
to appear in one place.
* It allows overriding builtin functions. For instance, to trace all
calls to ‘map’:
let
overrides = {
map = f: xs: builtins.trace "map called!" (map f xs);
# Ensure that our override gets propagated by calls to
# import/scopedImport.
import = fn: scopedImport overrides fn;
scopedImport = attrs: fn: scopedImport (overrides // attrs) fn;
# Also update ‘builtins’.
builtins = builtins // overrides;
};
in scopedImport overrides ./bla.nix
* Similarly, it allows extending the set of builtin functions. For
instance, during Nixpkgs/NixOS evaluation, the Nixpkgs library
functions could be added to the default scope.
There is a downside: calls to scopedImport are not memoized, unlike
import. So importing a file multiple times leads to multiple parsings
/ evaluations. It would be possible to construct the AST only once,
but that would require careful handling of variables/environments.
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For example:
error: `tail' called on an empty list, at
/home/eelco/Dev/nixpkgs/pkgs/applications/misc/hello/ex-2/default.nix:13:7
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This allows error messages like:
error: the anonymous function at `/etc/nixos/configuration.nix:1:1'
called without required argument `foo', at
`/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/lib/modules.nix:77:59'
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This reverts commit 273322c7732093a354e86df82cf75d6604b8bce8.
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Fixes #121. Note that we don't warn about missing $NIX_PATH entries
because it's intended that some may be missing (cf. the default
$NIX_PATH on NixOS, which includes paths like /etc/nixos/nixpkgs for
backward compatibility).
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I.e. an attribute set { file = <string>; line = <int>; column = <int>; }.
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The local Value object prevented g++ from making a tail call. Not
clear why. In any case, not using a temporary makes g++ do the tail
call.
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We don't have any other kind of sets so calling them attribute sets is
unnecessarily verbose.
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Messages like
while evaluating the attribute `outPath' at `/nix/store/212ngf4ph63mp6p1np2bapkfikpakfv7-nix-1.6/share/nix/corepkgs/derivation.nix:18:9':
are redundant, because Nix already shows that it's evaluating a derivation:
while instantiating the derivation named `firefox-24.0' at `/home/eelco/Dev/nixpkgs/pkgs/applications/networking/browsers/firefox/default.nix:131:5':
while evaluating the derivation attribute `nativeBuildInputs' at `/home/eelco/Dev/nixpkgs/pkgs/stdenv/generic/default.nix:76:17':
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So if you do "nix-env -qa -A nixos", then other channels won't be
parsed/evaluated at all.
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Since we already cache files in normal form (fileEvalCache), caching
parse trees is redundant.
Note that getting rid of this cache doesn't actually save much memory
at the moment, because parse trees are currently not freed / GC'ed.
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This reduces the difference between inherited and non-inherited
attribute handling to the choice of which env to use (in recs and lets)
by setting the AttrDef::e to a new ExprVar in the parser rather than
carrying a separate AttrDef::v VarRef member.
As an added bonus, this allows inherited attributes that inherit from a
with to delay forcing evaluation of the with's attributes.
Signed-off-by: Shea Levy <shea@shealevy.com>
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So on 64-bit systems, integers are now 64-bit.
Fixes #158.
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Commit 20866a7031ca823055a221653b77986faa167329 added a ‘withAttrs’
field to Env, which is annoying because it makes every Env structure
bigger and we allocate millions of them. E.g. NixOS evaluation took
18 MiB more. So this commit squeezes ‘withAttrs’ into values[0].
Probably should use a union...
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Signed-off-by: Shea Levy <shea@shealevy.com>
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Evaluation of attribute sets is strict in the attribute names, which
means immediate evaluation of `with` attribute sets rules out some
potentially interesting use cases (e.g. where the attribute names of one
set depend in some way on another but we want to bring those names into
scope for some values in the second set).
The major example of this is overridable self-referential package sets
(e.g. all-packages.nix). With immediate `with` evaluation, the only
options for such sets are to either make them non-recursive and
explicitly use the name of the overridden set in non-overridden one
every time you want to reference another package, or make the set
recursive and use the `__overrides` hack. As shown in the test case that
comes with this commit, though, delayed `with` evaluation allows a nicer
third alternative.
Signed-off-by: Shea Levy <shea@shealevy.com>
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We now print all output paths of a package, e.g.
openssl-1.0.0i bin=/nix/store/gq2mvh0wb9l90djvsagln3aqywqmr6vl-openssl-1.0.0i-bin;man=/nix/store/7zwf5r5hsdarl3n86dasvb4chm2xzw9n-openssl-1.0.0i-man;/nix/store/cj7xvk7fjp9q887359j75pw3pzjfmqf1-openssl-1.0.0i
or (in XML mode)
<item attrPath="openssl" name="openssl-1.0.0i" system="x86_64-linux">
<output name="bin" path="/nix/store/gq2mvh0wb9l90djvsagln3aqywqmr6vl-openssl-1.0.0i-bin" />
<output name="man" path="/nix/store/7zwf5r5hsdarl3n86dasvb4chm2xzw9n-openssl-1.0.0i-man" />
<output name="out" path="/nix/store/cj7xvk7fjp9q887359j75pw3pzjfmqf1-openssl-1.0.0i" />
</item>
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This allows adding attributes like
attr = if stdenv.system == "bla" then something else null;
without changing the resulting derivation on non-<bla> platforms.
We once considered adding a special "ignore" value for this purpose,
but using null seems more elegant.
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This allows repairing corrupted derivations and other source files.
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This can serve as a generic efficient list builder. For instance, the
function ‘catAttrs’ in Nixpkgs can be rewritten from
attr: l: fold (s: l: if hasAttr attr s then [(getAttr attr s)] ++ l else l) [] l
to
attr: l: builtins.concatLists (map (s: if hasAttr attr s then [(getAttr attr s)] else []) l)
Statistics before:
time elapsed: 1.08683
size of a value: 24
environments allocated: 1384376 (35809568 bytes)
list elements: 6946783 (55574264 bytes)
list concatenations: 37434
values allocated: 1760440 (42250560 bytes)
attribute sets allocated: 392040
right-biased unions: 186334
values copied in right-biased unions: 591137
symbols in symbol table: 18273
number of thunks: 1297673
number of thunks avoided: 1380759
number of attr lookups: 430802
number of primop calls: 628912
number of function calls: 1333544
Statistics after (including new catAttrs):
time elapsed: 0.959854
size of a value: 24
environments allocated: 1010198 (26829296 bytes)
list elements: 1984878 (15879024 bytes)
list concatenations: 30488
values allocated: 1589760 (38154240 bytes)
attribute sets allocated: 392040
right-biased unions: 186334
values copied in right-biased unions: 591137
symbols in symbol table: 18274
number of thunks: 1040925
number of thunks avoided: 1038428
number of attr lookups: 438419
number of primop calls: 474844
number of function calls: 959366
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Setting the environment variable NIX_COUNT_CALLS to 1 enables some
basic profiling in the evaluator. It will count calls to functions
and primops as well as evaluations of attributes.
For example, to see where evaluation of a NixOS configuration spends
its time:
$ NIX_SHOW_STATS=1 NIX_COUNT_CALLS=1 ./src/nix-instantiate/nix-instantiate '<nixos>' -A system --readonly-mode
...
calls to 39 primops:
239532 head
233962 tail
191252 hasAttr
...
calls to 1595 functions:
224157 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/lists.nix:17:19'
221767 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/lists.nix:17:14'
221767 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/lists.nix:17:10'
...
evaluations of 7088 attributes:
167377 undefined position
132459 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/attrsets.nix:119:41'
47322 `/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgs/pkgs/lib/attrsets.nix:13:21'
...
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EvalState::eval(). This gives a 12% speedup on ‘nix-instantiate
/etc/nixos/nixos/ -A system --readonly-mode’ (from 1.01s to 0.89s).
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and allocate them only once.
* Move Value and related functions into value.hh.
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/etc/nixos/nixos -A system" spent about 10% of its time in
dynamic_cast.
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prevents files from being evaluated and stored as values multiple
times. For instance, evaluation of the ‘system’ attribute in NixOS
causes ‘nixpkgs/pkgs/lib/lists.nix’ to be evaluated 2019 times.
Caching gives a modest speedup and a decent memory footprint
reduction (e.g., from 1.44s to 1.28s, and from 81 MiB to 59 MiB with
GC_INITIAL_HEAP_SIZE=100000 on my system).
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directory
/home/eelco/src/stdenv-updates
that you want to use as the directory for import such as
with (import <nixpkgs> { });
then you can say
$ nix-build -I nixpkgs=/home/eelco/src/stdenv-updates
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brackets, e.g.
import <nixpkgs/pkgs/lib>
are resolved by looking them up relative to the elements listed in
the search path. This allows us to get rid of hacks like
import "${builtins.getEnv "NIXPKGS_ALL"}/pkgs/lib"
The search path can be specified through the ‘-I’ command-line flag
and through the colon-separated ‘NIX_PATH’ environment variable,
e.g.,
$ nix-build -I /etc/nixos ...
If a file is not found in the search path, an error message is
lazily thrown.
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