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lib/modules: implement a way to override a property based on its previous value #286578

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101 changes: 63 additions & 38 deletions lib/modules.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -817,46 +817,63 @@ let
};

# Merge definitions of a value of a given type.
mergeDefinitions = loc: type: defs: rec {
defsFinal' =
let
# Process mkMerge and mkIf properties.
defs' = concatMap (m:
map (value: { inherit (m) file; inherit value; }) (builtins.addErrorContext "while evaluating definitions from `${m.file}':" (dischargeProperties m.value))
) defs;

# Process mkOverride properties.
defs'' = filterOverrides' defs';

# Sort mkOrder properties.
defs''' =
# Avoid sorting if we don't have to.
if any (def: def.value._type or "" == "order") defs''.values
then sortProperties defs''.values
else defs''.values;
in {
values = defs''';
inherit (defs'') highestPrio;
};
defsFinal = defsFinal'.values;

# Type-check the remaining definitions, and merge them. Or throw if no definitions.
mergedValue =
if isDefined then
if all (def: type.check def.value) defsFinal then type.merge loc defsFinal
else let allInvalid = filter (def: ! type.check def.value) defsFinal;
in throw "A definition for option `${showOption loc}' is not of type `${type.description}'. Definition values:${showDefs allInvalid}"
else
# (nixos-option detects this specific error message and gives it special
# handling. If changed here, please change it there too.)
throw "The option `${showOption loc}' is used but not defined.";
mergeDefinitions = loc: type: defs: let
# Process mkMerge and mkIf properties.
defs' = concatMap (m:
map (value: { inherit (m) file; inherit value; }) (builtins.addErrorContext "while evaluating definitions from `${m.file}':" (dischargeProperties m.value))
) defs;
getPrio = def: if lib.elem def.value._type or "" [ "override" "overrideWith" ] then def.value.priority else defaultOverridePriority;
highestPrioBelow = thresh: foldl' (prio: def: let p = getPrio def; in if p <= thresh then prio else (min p prio)) 9999 defs';
highestPrio = highestPrioBelow (-1);
filterOverrides = prio: let
strip = def: if def.value._type or "" == "override" then def // { value = def.value.content; } else def;
in {
values = concatMap (def: if getPrio def == prio then [(strip def)] else []) defs';
highestPrio = prio;
};
mergedForPrio = prio: rec {
defsFinal' =
let
# Process mkOverride properties.
defs'' = filterOverrides prio;

# Process mkOverrideWith
defs''' = let
p = highestPrioBelow prio;
mergedBelow = mergedForPrio p;
mapOverrideWith = def: def // { value = def.value.fn mergedBelow.mergedValue; };
in map (def: if def.value._type or "" == "overrideWith" then mapOverrideWith def else def) defs''.values;

# Sort mkOrder properties.
defs'''' =
# Avoid sorting if we don't have to.
if any (def: def.value._type or "" == "order") defs'''
then sortProperties defs'''
else defs''';
in {
values = defs'''';
inherit (defs'') highestPrio;
};
defsFinal = defsFinal'.values;

# Type-check the remaining definitions, and merge them. Or throw if no definitions.
mergedValue =
if isDefined then
if all (def: type.check def.value) defsFinal then type.merge loc defsFinal
else let allInvalid = filter (def: ! type.check def.value) defsFinal;
in throw "A definition for option `${showOption loc}' is not of type `${type.description}'. Definition values:${showDefs allInvalid}"
else
# (nixos-option detects this specific error message and gives it special
# handling. If changed here, please change it there too.)
throw "The option `${showOption loc}' is used but not defined.";

isDefined = defsFinal != [];
isDefined = defsFinal != [];

optionalValue =
if isDefined then { value = mergedValue; }
else {};
};
optionalValue =
if isDefined then { value = mergedValue; }
else {};
};
in mergedForPrio highestPrio;

/* Given a config set, expand mkMerge properties, and push down the
other properties into the children. The result is a list of
Expand Down Expand Up @@ -1016,11 +1033,17 @@ let
inherit priority content;
};

mkOverrideWith = priority: fn:
{ _type = "overrideWith";
inherit priority fn;
};

mkOptionDefault = mkOverride 1500; # priority of option defaults
mkDefault = mkOverride 1000; # used in config sections of non-user modules to set a default
defaultOverridePriority = 100;
mkImageMediaOverride = mkOverride 60; # image media profiles can be derived by inclusion into host config, hence needing to override host config, but do allow user to mkForce
mkForce = mkOverride 50;
mkForceWith = mkOverrideWith 50;
mkVMOverride = mkOverride 10; # used by ‘nixos-rebuild build-vm’

defaultPriority = lib.warnIf (lib.isInOldestRelease 2305) "lib.modules.defaultPriority is deprecated, please use lib.modules.defaultOverridePriority instead." defaultOverridePriority;
Expand Down Expand Up @@ -1351,13 +1374,15 @@ private //
mkDerivedConfig
mkFixStrictness
mkForce
mkForceWith
mkIf
mkImageMediaOverride
mkMerge
mkMergedOptionModule
mkOptionDefault
mkOrder
mkOverride
mkOverrideWith
mkRemovedOptionModule
mkRenamedOptionModule
mkRenamedOptionModuleWith
Expand Down