I recently wrote some Nix code where I wrongly set a value to an option
which wasn't an actual option, but an attr-set of options. The mistake I
made can be demonstrated with an expression like this:
{
foo = { lib, pkgs, config, ... }: with lib; {
options.foo.bar.baz = mkOption {
type = types.str;
};
config.foo.bar = 23;
};
}
While it wasn't too hard to find the cause of the mistake for me, it was
necessary to have some practice in reading stack traces from the module
system since the eval-error I got was not very helpful:
error: --- TypeError --------------------------------------------------------- nix-build
at: (323:25) in file: /nix/store/3nm31brdz95pj8gch5gms6xwqh0xx55c-source/lib/modules.nix
322| foldl' (acc: module:
323| acc // (mapAttrs (n: v:
| ^
324| (acc.${n} or []) ++ f module v
value is an integer while a set was expected
(use '--show-trace' to show detailed location information)
I figured that such an error can be fairly confusing for someone who's
new to NixOS, so I decided to catch this case in th `byName` function in
`lib/modules.nix` by checking if the value to map through is an actual
attr-set. If not, a different error will be thrown.
For renames like
mkAliasOptionModule [ "services" "compton" ] [ "services" "picom" ]
where the target is an option set (like services.picom) instead of a single
option (like services.picom.enable), previously the renamed option type
was unset, leading to it being `types.unspecified`.
This changes it to be `types.submodule {}` instead, which makes more
sense.
Previously the .enable option was used to encode the condition as well,
which lead to some oddness:
- In order to encode an assertion, one had to invert it
- To disable a check, one had to mkForce it
By introducing a separate .check option this is solved because:
- It can be used to encode assertions
- Disabling is done separately with .enable option, whose default can be
overridden without a mkForce
Previously this option was thought to be necessary to avoid infinite
recursion, but it actually isn't, since the check evaluation isn't fed
back into the module fixed-point.
This implements assertions/warnings supported by the module system directly,
instead of just being a NixOS option (see
nixos/modules/misc/assertions.nix).
This has the following benefits:
- It allows cleanly redoing the user interface. The new
implementation specifically allows disabling assertions or
converting them to warnings instead.
- Assertions/warnings can now be thrown easily from within
submodules, which previously wasn't possible and needed workarounds.
Nix can perform static scope checking, but whenever code is inside
a `with` expression, the analysis breaks down, because it can't
know statically what's in the attribute set whose attributes were
brought into scope. In those cases, Nix has to assume that
everything works out.
Except it doesnt. Removing `with` from lib/ revealed an undefined
variable in an error message.
If that doesn't convince you that we're better off without `with`,
I can tell you that this PR results in a 3% evaluation performance
improvement because Nix can look up local variables by index.
This adds up with applications like the module system.
Furthermore, removing `with` makes the binding site of each
variable obvious, which helps with comprehension.
Previously if `_file` was specified by a module:
trace: warning: The type `types.string' of option `foo' defined in `/nix/store/yxhm2il5yrb92fldgriw0wyqh2kk9qyc-bug.nix' is deprecated. See https://github.com/NixOS/nixpkgs/pull/66346 for better alternative types.
With this change:
trace: warning: The type `types.string' of option `foo' defined in `/home/infinisil/src/nixpkgs/bug.nix' is deprecated. See https://github.com/NixOS/nixpkgs/pull/66346 for better alternative types.
If multiple definitions are passed, this evaluates them all as if they
were the only one, for a better error message. In particular this won't
show module-internal properties like `_type = "override"` and co.
The vision here is that configuration tools can generate .json or .toml
files, which can be plugged into an existing configuration.
Eg:
{ lib, ... }:
{
imports = [
(lib.modules.importJSON ./hardware-configuration.json)
];
}
Previously the only way to deprecate a type was using
theType = lib.warn "deprecated" (mkOptionType ...)
This caused the warning to be emitted when the type was evaluated, but
the error didn't include which option actually used that type.
With this commit, types can specify a deprecationMessage, which when
non-null, is printed along with the option that uses the type
An easy-to-make mistake when declaring e.g. a submodule is the accidental
confusion of `options` and `config`:
types.submodule {
config = {
foo = mkOption { /* ... */ };
};
}
However the error-message
The option `[definition 1-entry 1].foo' defined in `<expr.nix>' does not exist.
is fairly unhelpful because it seems as the options are declared at the
first sight. In fact, it took a colleague and me a while to track down such
a mistake a few days ago and we both agreed that this should be somehow caught
to save the time we spent debugging the module in question.
At first I decided to catch this error in the `submodules`-type directly
by checking whether `options` is undeclared, however this becomes fairly
complicated as soon as a submodule-declaration e.g. depends on existing
`config`-values which would've lead to some ugly `builtins.tryExec`-heuristic.
This patch now simply checks if the option's prefix has any options
defined if a point in evaluation is reached where it's clear that the
option in question doesn't exist. This means that this patch doesn't
change the logic of the module system, it only provides a more detailed
error in certain cases:
The option `[definition 1-entry 1].foo' defined in `<expr.nix>' does not exist.
However it seems as there are no options defined in [definition 1-entry 1]. Are you sure you've
declared your options properly? This happens if you e.g. declared your options in `types.submodule'
under `config' rather than `options'.
The refactoring in fd75dc8765
introduced a mistake in the error message that doesn't show the full
context anymore. E.g. with this module:
options.foo.bar = lib.mkOption {
type = lib.types.submodule {
baz = 10;
};
default = {};
};
You'd get the error
The option `baz' defined in `/home/infinisil/src/nixpkgs/config.nix' does not exist.
instead of the previous
The option `foo.bar.baz' defined in `/home/infinisil/src/nixpkgs/config.nix' does not exist.
This commit undoes this regression
For programs that have a lot of (Nix-representable) configuration options,
a simple way to represent this in a NixOS module is to declare an
option of a type like `attrsOf str`, representing a key-value mapping
which then gets generated into a config file. However with such a type,
there's no way to add type checking for only some key values.
On the other end of the spectrum, one can declare a single separate
option for every key value that the program supports, ending up with a module
with potentially 100s of options. This has the benefit that every value
gets type checked, catching mistakes at evaluation time already. However
the disadvantage is that the module becomes big, becomes coupled to the
program version and takes a lot of effort to write and maintain.
Previously there was a middle ground between these two
extremes: Declare an option of a type like `attrsOf str`, but declare
additional separate options for the values you wish to have type
checked, and assign their values to the `attrsOf str` option. While this
works decently, it has the problem of duplicated options, since now both
the additional options and the `attrsOf str` option can be used to set a
key value. This leads to confusion about what should happen if both are
set, which defaults should apply, and more.
Now with this change, a middle ground becomes available that solves above
problems: The module system now supports setting a freeform type, which
gets used for all definitions that don't have an associated option. This
means that you can now declare all options you wish to have type
checked, while for the rest a freeform type like `attrsOf str` can be
used.
This fundamentally changes how the module evaluation internally
handles definitions without an associated option.
Previously the values of these definitions were discarded and only
the names were propagated. This was fine because that's all that's
needed for optionally checking whether all definitions have an
associated option with _module.check.
However with the upcoming change of supporting freeform modules,
we *do* need the values of these.
With this change, the module evaluation cleanly separates definitions
that match an option, and ones that do not.
The _module option is added as an internal option set, and it messes up
the results of module evaluations, requiring people to manually filter
_modules out.
If people depend on this, they can still use config._module from inside
the modules, exposing _module as an explicitly declared user option. Or
alternatively with the _module attribute now returned by evalModules.
This helps with troubleshooting exceptions in config values, which were hard
to track down for options with many definitions.
The trace will look like:
error: while evaluating the attribute 'config.foo' at undefined position:
[...]
while evaluating the option `foo':
[...]
while evaluating definitions from `/home/user/mymod.nix':
while evaluating 'dischargeProperties' at /home/user/nixpkgs/lib/modules.nix:464:25, called from /home/user/nixpkgs/lib/modules.nix:392:137:
while evaluating the attribute 'value' at /home/user/nixpkgs/lib/modules.nix:277:44:
Value error!
where the `/home/user/mymod.nix` module is
{ lib, ... }: {
options.foo = lib.mkOption {
type = lib.types.lines;
};
config.foo = builtins.throw "Value error!";
}
Without this change, accessing `mergedValue` from `mergeDefinitions` in
case there are no definitions will throw an error like
error: evaluation aborted with the following error message: 'This case should never happen.'
This change makes it throw the appropriate error
error: The option `foo' is used but not defined.
This is fully backwards compatible.
This fixes imports from the store not being possible, which was caused by
https://github.com/NixOS/nixpkgs/pull/76857
E.g. such a case:
imports = [ "${home-manager}/nixos" ];
With this change, disabledModules applies recursively, meaning if you
have a module "foo.nix" with
imports = [ ./bar.nix ];
then setting
disabledModules = [ "foo.nix" ];
will disable both "foo.nix" and "bar.nix", whereas previously only
"foo.nix" would be disabled.
This change along with https://github.com/NixOS/nixpkgs/pull/61570 allows
modules to be fully disabled even when they have some `mkRenamedOption`
imports.
If I understand correctly, the problem isn't so much that you're assigning to
that top-level attribute, but that the assignment to the attribute (or any
child of the attribute) introduces the 'config' object and prevents 'lifting'
all settings to a generated 'config' object.
