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>
Certain desugaring schemes may require the parser to use some builtin
function to do some of the work (e.g. currently `throw` is used to
lazily cause an error if a `<>`-style path is not in the search path)
Unfortunately, these names are not reserved keywords, so an expression
that uses such a syntactic sugar will not see the expected behavior
(see tests/lang/eval-okay-redefine-builtin.nix for an example).
This adds the ExprBuiltin AST type, which when evaluated uses the value
from the rootmost variable scope (which of course is initialized
internally and can't shadow any of the builtins).
Signed-off-by: Shea Levy <shea@shealevy.com>
Antiquotes should evaluate to strings or paths. This is usually
checked, except in the case where the antiquote makes up the entire
string, as in "${expr}". This is optimised to expr, which discards
the runtime type checks / coercions.
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>
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>
In Nixpkgs, the attribute in all-packages.nix corresponding to a
package is usually equal to the package name. However, this doesn't
work if the package contains a dash, which is fairly common. The
convention is to replace the dash with an underscore (e.g. "dbus-lib"
becomes "dbus_glib"), but that's annoying. So now dashes are valid in
variable / attribute names, allowing you to write:
dbus-glib = callPackage ../development/libraries/dbus-glib { };
and
buildInputs = [ dbus-glib ];
Since we don't have a negation or subtraction operation in Nix, this
is unambiguous.
other simplifications.
* Use <nix/...> to locate the corepkgs. This allows them to be
overriden through $NIX_PATH.
* Use bash's pipefail option in the NAR builder so that we don't need
to create a temporary file.
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
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.
check' now succeeds :-)
* An attribute set such as `{ foo = { enable = true; };
foo.port = 23; }' now parses. It was previously rejected, but I'm
too lazy to implement the check. (The only reason to reject it is
that the reverse, `{ foo.port = 23; foo = { enable = true; }; }', is
rejected, which is kind of ugly.)
* src/libexpr/expr-to-xml.cc (nix::showAttrs): Add `location'
parameter. Provide location XML attributes when it's true. Update
callers.
(nix::printTermAsXML): Likewise.
* src/libexpr/expr-to-xml.hh (nix::printTermAsXML): Update prototype;
have `location' default to `false'.
* src/nix-instantiate/nix-instantiate.cc (printResult, processExpr): Add
`location' parameter; update callers.
(run): Add support for `--no-location'.
* src/nix-instantiate/help.txt: Update accordingly.
* tests/lang.sh: Invoke `nix-instantiate' with `--no-location' for the
XML tests.
* tests/lang/eval-okay-toxml.exp, tests/lang/eval-okay-to-xml.nix: New
files.
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.
intersectAttrs returns the (right-biased) intersection between two
attribute sets, e.g. every attribute from the second set that also
exists in the first. functionArgs returns the set of attributes
expected by a function.
The main goal of these is to allow the elimination of most of
all-packages.nix. Most package instantiations in all-packages.nix
have this form:
foo = import ./foo.nix {
inherit a b c;
};
With intersectAttrs and functionArgs, this can be written as:
foo = callPackage (import ./foo.nix) { };
where
callPackage = f: args:
f ((builtins.intersectAttrs (builtins.functionArgs f) pkgs) // args);
I.e., foo.nix is called with all attributes from "pkgs" that it
actually needs (e.g., pkgs.a, pkgs.b and pkgs.c). (callPackage can
do any other generic package-level stuff we might want, such as
applying makeOverridable.) Of course, the automatically supplied
arguments can be overriden if needed, e.g.
foo = callPackage (import ./foo.nix) {
c = c_version_2;
};
but for the vast majority of packages, this won't be needed.
The advantages are to reduce the amount of typing needed to add a
dependency (from three sites to two), and to reduce the number of
trivial commits to all-packages.nix. For the former, there have
been two previous attempts:
- Use "args: with args;" in the package's function definition.
This however obscures the actual expected arguments of a
function, which is very bad.
- Use "{ arg1, arg2, ... }:" in the package's function definition
(i.e. use the ellipis "..." to allow arbitrary additional
arguments), and then call the function with all of "pkgs" as an
argument. But this inhibits error detection if you call it with
an misspelled (or obsolete) argument.
attributes of the rec are in scope of `e'. This is useful in
expressions such as
rec {
lib = import ./lib;
inherit (lib) concatStrings;
}
It does change the semantics of expressions such as
let x = {y = 1;}; in rec { x = {y = 2;}; inherit (x) y; }.y
This now returns 2 instead of 1. However, no code in Nixpkgs or
NixOS seems to rely on the old behaviour.
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'.
