diff --git a/lib/default.nix b/lib/default.nix index d2239d26ead..e3c1ed71346 100644 --- a/lib/default.nix +++ b/lib/default.nix @@ -5,7 +5,7 @@ */ let - inherit (import ./fixed-points.nix {}) makeExtensible; + inherit (import ./fixed-points.nix { inherit lib; }) makeExtensible; lib = makeExtensible (self: let callLibs = file: import file { lib = self; }; @@ -69,7 +69,7 @@ let importJSON importTOML warn info showWarnings nixpkgsVersion version mod compare splitByAndCompare functionArgs setFunctionArgs isFunction toHexString toBaseDigits; inherit (self.fixedPoints) fix fix' converge extends composeExtensions - makeExtensible makeExtensibleWithCustomName; + composeManyExtensions makeExtensible makeExtensibleWithCustomName; inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath getAttrFromPath attrVals attrValues getAttrs catAttrs filterAttrs filterAttrsRecursive foldAttrs collect nameValuePair mapAttrs diff --git a/lib/fixed-points.nix b/lib/fixed-points.nix index 968930526a6..f998bc74e1d 100644 --- a/lib/fixed-points.nix +++ b/lib/fixed-points.nix @@ -1,4 +1,4 @@ -{ ... }: +{ lib, ... }: rec { # Compute the fixed point of the given function `f`, which is usually an # attribute set that expects its final, non-recursive representation as an @@ -77,6 +77,15 @@ rec { super' = super // fApplied; in fApplied // g self super'; + # Compose several extending functions of the type expected by 'extends' into + # one where changes made in preceding functions are made available to + # subsequent ones. + # + # composeManyExtensions : [packageSet -> packageSet -> packageSet] -> packageSet -> packageSet -> packageSet + # ^final ^prev ^overrides ^final ^prev ^overrides + composeManyExtensions = + lib.foldr (x: y: composeExtensions x y) (self: super: {}); + # Create an overridable, recursive attribute set. For example: # # nix-repl> obj = makeExtensible (self: { }) diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix index 6175f15819a..35a5801c724 100644 --- a/lib/tests/misc.nix +++ b/lib/tests/misc.nix @@ -87,6 +87,26 @@ runTests { expected = true; }; + testComposeManyExtensions0 = { + expr = let obj = makeExtensible (self: { foo = true; }); + emptyComposition = composeManyExtensions []; + composed = obj.extend emptyComposition; + in composed.foo; + expected = true; + }; + + testComposeManyExtensions = + let f = self: super: { bar = false; baz = true; }; + g = self: super: { bar = super.baz or false; }; + h = self: super: { qux = super.bar or false; }; + obj = makeExtensible (self: { foo = self.qux; }); + in { + expr = let composition = composeManyExtensions [f g h]; + composed = obj.extend composition; + in composed.foo; + expected = (obj.extend (composeExtensions f (composeExtensions g h))).foo; + }; + testBitAnd = { expr = (bitAnd 3 10); expected = 2;