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nixos/nixpkgs: add override/merging capabilities from the module system to the nixpkgs.config option #80582

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nixos/nixpkgs: add override/merging capabilities from the module system to the nixpkgs.config option #80582

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75 changes: 50 additions & 25 deletions nixos/modules/misc/nixpkgs.nix
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Expand Up @@ -14,32 +14,57 @@ let
then f x
else f;

mergeConfig = lhs_: rhs_:
let
lhs = optCall lhs_ { inherit pkgs; };
rhs = optCall rhs_ { inherit pkgs; };
in
recursiveUpdate lhs rhs //
optionalAttrs (lhs ? packageOverrides) {
packageOverrides = pkgs:
optCall lhs.packageOverrides pkgs //
optCall (attrByPath ["packageOverrides"] ({}) rhs) pkgs;
} //
optionalAttrs (lhs ? perlPackageOverrides) {
perlPackageOverrides = pkgs:
optCall lhs.perlPackageOverrides pkgs //
optCall (attrByPath ["perlPackageOverrides"] ({}) rhs) pkgs;
};

configType = mkOptionType {
mergableConfigType = mkOptionType {
name = "nixpkgs-config";
description = "nixpkgs config";
check = x:
let traceXIfNot = c:
if c x then true
else lib.traceSeqN 1 x false;
in traceXIfNot isConfig;
merge = args: fold (def: mergeConfig def.value) {};
check = isConfig;
merge = loc: defs:
let
# Ensure that each attribute from nixpkgs.config appears at the
# first iteration to make sure that nothing is lost.
allValues = fold recursiveUpdate {} defs;
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I'm aware that this is a gross hack to make sure that any attr-names that are defined in any moduel taken into account is known to the merger. Are there any suggestions for a better workaround? :)


# Recurses through the `config` attr-set for nixpkgs and ensures that
# no conflicting definitions exist and that overrides are resolved properly.
mapFun = path: value:
if isAttrs value && !(value ? _type) then value
else let
# Evaluate mkIf/mkMerge with `lib.dischargeProperties` and append the
# value to the list of declarations. If a value is `null`, it means that
# it was not declared in one of the configs and can be ignored.
appendVal = all: value_: next:
let
# FIXME support `mkMerge [{ snens = mkIf cond val; }]`
discharged = dischargeProperties value_;
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As mentioned in the comment, mk{If,Merge,Before,...} aren't evaluated inside a mkMerge (mkMerge [ (mkIf cond { /* ... */ } ]) works fine though). IMHO this would make the code even more complex, but are there any suggestions how fix this? :)

# FIXME check if there's a case where `discharged` is `[]` and
# therefore breaks `head`.
value = let h = head discharged; in if isAttrs h
then foldl recursiveUpdate {} discharged
else h;
in all ++ (if value == null then [] else [{
inherit (next) file;
inherit value;
}]);

# Gather all declarations of a value in the `nixpkgs.config` attr-set.
allDeclarations = foldl
(all: next: appendVal all (optCall (attrByPath path null next) finalPkgs) next)
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The optCall in the recursive mapAttrs replaces the merging behavior for {perlP,p}ackageOverrides. Please note that I'm now using finalPkgs rather than pkgs as this seems more appropriate to me (since finalPkgs also takes overlays into account). If this is a wrong decision, please let me know, we probably might want to use pkgs rather than finalPkgs here.

[]
defs;

# Evaluate all overrides (defined using mkOverride/mkForce/etc) and pick the
# value with the highes priority.
result = sortProperties (filterOverrides allDeclarations);

# Merge all declarations (if a list or an attr-set is given, those can be merged together),
# if a "unique" value is given, it's ensured that no conflicting definitions exist.
#
# FIXME This is missing support for separatedString!
merge = let h = (head result).value or null; in
if isList h || isAttrs h then mergeDefaultOption else mergeOneOption;
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As mentioned in the comment, separatedString doesn't work here. As recursiveUpdate did silent overrides, this never worked before, but are there any suggestions how to fix this as well? :)

in
merge (["nixpkgs" "config"] ++ (tail path)) result;
in mapAttrsRecursiveCond (x: !(x ? _type)) mapFun allValues;
};

overlayType = mkOptionType {
Expand Down Expand Up @@ -113,7 +138,7 @@ in
''
{ allowBroken = true; allowUnfree = true; }
'';
type = configType;
type = mergableConfigType;
description = ''
The configuration of the Nix Packages collection. (For
details, see the Nixpkgs documentation.) It allows you to set
Expand Down