diff --git a/lib/customisation.nix b/lib/customisation.nix index 7be412bac353..66638b63342a 100644 --- a/lib/customisation.nix +++ b/lib/customisation.nix @@ -306,18 +306,129 @@ rec { in if drv == null then null else deepSeq drv' drv'; - /* Make a set of packages with a common scope. All packages called - with the provided `callPackage` will be evaluated with the same - arguments. Any package in the set may depend on any other. The - `overrideScope'` function allows subsequent modification of the package - set in a consistent way, i.e. all packages in the set will be - called with the overridden packages. The package sets may be - hierarchical: the packages in the set are called with the scope - provided by `newScope` and the set provides a `newScope` attribute - which can form the parent scope for later package sets. + /** + Make an attribute set (a "scope") from functions that take arguments from that same attribute set. + See [](#ex-makeScope) for how to use it. - Type: - makeScope :: (AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a) -> (AttrSet -> AttrSet) -> AttrSet + # Inputs + + 1. `newScope` (`AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a`) + + A function that takes an attribute set `attrs` and returns what ends up as `callPackage` in the output. + + Typical values are `callPackageWith` or the output attribute `newScope`. + + 2. `f` (`AttrSet -> AttrSet`) + + A function that takes an attribute set as returned by `makeScope newScope f` (a "scope") and returns any attribute set. + + This function is used to compute the fixpoint of the resulting scope using `callPackage`. + Its argument is the lazily evaluated reference to the value of that fixpoint, and is typically called `self` or `final`. + + See [](#ex-makeScope) for how to use it. + See [](#sec-functions-library-fixedPoints) for details on fixpoint computation. + + # Output + + `makeScope` returns an attribute set of a form called `scope`, which also contains the final attributes produced by `f`: + + ``` + scope :: { + callPackage :: ((AttrSet -> a) | Path) -> AttrSet -> a + newScope = AttrSet -> scope + overrideScope = (scope -> scope -> AttrSet) -> scope + packages :: AttrSet -> AttrSet + } + ``` + + - `callPackage` (`((AttrSet -> a) | Path) -> AttrSet -> a`) + + A function that + + 1. Takes a function `p`, or a path to a Nix file that contains a function `p`, which takes an attribute set and returns value of arbitrary type `a`, + 2. Takes an attribute set `args` with explicit attributes to pass to `p`, + 3. Calls `f` with attributes from the original attribute set `attrs` passed to `newScope` updated with `args, i.e. `attrs // args`, if they match the attributes in the argument of `p`. + + All such functions `p` will be called with the same value for `attrs`. + + See [](#ex-makeScope-callPackage) for how to use it. + + - `newScope` (`AttrSet -> scope`) + + Takes an attribute set `attrs` and returns a scope that extends the original scope. + + - `overrideScope` (`(scope -> scope -> AttrSet) -> scope`) + + Takes a function `g` of the form `final: prev: { # attributes }` to act as an overlay on `f`, and returns a new scope with values determined by `extends g f`. + See [](https://nixos.org/manual/nixpkgs/unstable/#function-library-lib.fixedPoints.extends) for details. + + This allows subsequent modification of the final attribute set in a consistent way, i.e. all functions `p` invoked with `callPackage` will be called with the modified values. + + - `packages` (`AttrSet -> AttrSet`) + + The value of the argument `f` to `makeScope`. + + - final attributes + + The final values returned by `f`. + + # Examples + + :::{#ex-makeScope .example} + # Create an interdependent package set on top of `pkgs` + + The functions in `foo.nix` and `bar.nix` can depend on each other, in the sense that `foo.nix` can contain a function that expects `bar` as an attribute in its argument. + + ```nix + let + pkgs = import { }; + in + pkgs.lib.makeScope pkgs.newScope (self: { + foo = self.callPackage ./foo.nix { }; + bar = self.callPackage ./bar.nix { }; + }) + ``` + + evaluates to + + ```nix + { + callPackage = «lambda»; + newScope = «lambda»; + overrideScope = «lambda»; + packages = «lambda»; + foo = «derivation»; + bar = «derivation»; + } + ``` + ::: + + :::{#ex-makeScope-callPackage .example} + # Using `callPackage` from a scope + + ```nix + let + pkgs = import { }; + inherit (pkgs) lib; + scope = lib.makeScope lib.callPackageWith (self: { a = 1; b = 2; }); + three = scope.callPackage ({ a, b }: a + b) { }; + four = scope.callPackage ({ a, b }: a + b) { a = 2; }; + in + [ three four ] + ``` + + evaluates to + + ```nix + [ 3 4 ] + ``` + ::: + + # Type + + ``` + makeScope :: (AttrSet -> ((AttrSet -> a) | Path) -> AttrSet -> a) -> (AttrSet -> AttrSet) -> scope + ``` */ makeScope = newScope: f: let self = f self // {