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modules: Update evalModules doc

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Robert Hensing 2021-10-29 14:58:28 +02:00
parent 22584ce667
commit 86f5136baf
1 changed files with 26 additions and 3 deletions
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lib/modules.nix
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@ -52,9 +52,32 @@ in
rec {
/* Evaluate a set of modules. The result is a set of two
attributes: ‘options’: the nested set of all option declarations,
and ‘config’: the nested set of all option values.
/*
Evaluate a set of modules. The result is a set with the attributes:
‘options’: The nested set of all option declarations,
‘config’: The nested set of all option values.
‘type’: A module system type representing the module set as a submodule,
to be extended by configuration from the containing module set.
‘extendModules’: A function similar to ‘evalModules’ but building on top
of the module set. Its arguments, ‘modules’ and ‘specialArgs’ are
added to the existing values.
Using ‘extendModules’ a few times has no performance impact as long
as you only reference the final ‘options’ and ‘config’.
If you do reference multiple ‘config’ (or ‘options’) from before and
after ‘extendModules’, performance is the same as with multiple
‘evalModules’ invocations, because the new modules' ability to
override existing configuration fundamentally requires a new
fixpoint to be constructed.
‘_module’: A portion of the configuration tree which is elided from
‘config’. It contains some values that are mostly internal to the
module system implementation.
!!! Please think twice before adding to this argument list! The more
that is specified here instead of in the modules themselves the harder
it is to transparently move a set of modules to be a submodule of another