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Fixes #294.
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allow-arbitrary-code-during-evaluation option is true (default false)
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This can be used to import a dynamic shared object and return an
arbitrary value, including new primops. This can be used both to test
new primops without having to recompile nix every time, and to build
specialized primops that probably don't belong upstream (e.g. a function
that calls out to gpg to decrypt a nixops secret as-needed).
The imported function should initialize the Value & as needed. A single
import can define multiple values by creating an attrset or list, of
course.
An example initialization function might look like:
extern "C" void initialize(nix::EvalState & state, nix::Value & v)
{
v.type = nix::tPrimOp;
v.primOp = NEW nix::PrimOp(myFun, 1, state.symbols.create("myFun"));
}
Then `builtins.importNative ./example.so "initialize"` will evaluate to
the primop defined in the myFun function.
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We're not catching these anywhere.
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In addition to reducing duplication, this fixes both import from
derivation and import of derivation for scopedImport
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There really is no case I can think of where taking the context into
account is useful. Mostly it's just very inconvenient.
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It's slower than ExprVar since it doesn't compute a static
displacement. Since we're not using the throw primop in the
implementation of <...> anymore, it's also not really needed.
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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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It contains the Nix expression search path as a list of { prefix, path
} sets, e.g.
[ { path = "/nix/var/nix/profiles/per-user/root/channels/nixos"; prefix = ""; }
{ path = "/etc/nixos/configuration.nix"; prefix = "nixos-config"; }
{ path = "/home/eelco/Dev/nix/inst/share/nix/corepkgs"; prefix = "nix"; }
]
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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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Otherwise you just get ‘expected string `Derive(['’ which isn't very helpful.
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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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The newEnv variable was accessed (via the dynamicEnv) pointer after it
had gone out of scope.
Fixes #234.
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This reverts commit 273322c7732093a354e86df82cf75d6604b8bce8.
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If we're evaluating some application ‘v = f x’, we can't store ‘f’
temporarily in ‘v’, because if ‘f x’ refers to ‘v’, it will get ‘f’
rather than an infinite recursion error.
Unfortunately, this breaks the tail call optimisation introduced in
c897bac54954373f63511702731fe2cb23c0c98e.
Fixes #217.
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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
$NIX_PATH on NixOS, which includes paths like /etc/nixos/nixpkgs for
backward compatibility).
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Conflicts:
src/libexpr/eval.cc
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Signed-off-by: Shea Levy <shea@shealevy.com>
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Now, in addition to a."${b}".c, you can write a.${b}.c (applicable
wherever dynamic attributes are valid).
Signed-off-by: Shea Levy <shea@shealevy.com>
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This doesn't change any functionality but moves some behavior out of the
parser and into the evaluator in order to simplify the code.
Signed-off-by: Shea Levy <shea@shealevy.com>
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Since addAttr has to iterate through the AttrPath we pass it, it makes
more sense to just iterate through the AttrNames in addAttr instead. As
an added bonus, this allows attrsets where two dynamic attribute paths
have the same static leading part (see added test case for an example
that failed previously).
Signed-off-by: Shea Levy <shea@shealevy.com>
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This adds new syntax for attribute names:
* attrs."${name}" => getAttr name attrs
* attrs ? "${name}" => isAttrs attrs && hasAttr attrs name
* attrs."${name}" or def => if attrs ? "${name}" then attrs."${name}" else def
* { "${name}" = value; } => listToAttrs [{ inherit name value; }]
Of course, it's a bit more complicated than that. The attribute chains
can be arbitrarily long and contain combinations of static and dynamic
parts (e.g. attrs."${foo}".bar."${baz}" or qux), which is relatively
straightforward for the getAttrs/hasAttrs cases but is more complex for
the listToAttrs case due to rules about duplicate attribute definitions.
For attribute sets with dynamic attribute names, duplicate static
attributes are detected at parse time while duplicate dynamic attributes
are detected when the attribute set is forced. So, for example, { a =
null; a.b = null; "${"c"}" = true; } will be a parse-time error, while
{ a = {}; "${"a"}".b = null; c = true; } will be an eval-time error
(technically that case could theoretically be detected at parse time,
but the general case would require full evaluation). Moreover, duplicate
dynamic attributes are not allowed even in cases where they would be
with static attributes ({ a.b.d = true; a.b.c = false; } is legal, but {
a."${"b"}".d = true; a."${"b"}".c = false; } is not). This restriction
might be relaxed in the future in cases where the static variant would
not be an error, but it is not obvious that that is desirable.
Finally, recursive attribute sets with dynamic attributes have the
static attributes in scope but not the dynamic ones. So rec { a = true;
"${"b"}" = a; } is equivalent to { a = true; b = true; } but rec {
"${"a"}" = true; b = a; } would be an error or use a from the
surrounding scope if it exists.
Note that the getAttr, getAttr or default, and hasAttr are all
implemented purely in the parser as syntactic sugar, while attribute
sets with dynamic attribute names required changes to the AST to be
implemented cleanly.
This is an alternative solution to and closes #167
Signed-off-by: Shea Levy <shea@shealevy.com>
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