mirror of
https://github.com/SebastianWendel/nixpkgs.git
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67b1265fb3
Suppose I have a Gemfile like this:
source "https://rubygems.org"
gem "actioncable"
gem "websocket-driver", group: :test
The gemset.nix generated by Bundix 2.4.1 will set ActionCable's groups
to [ "default" ], and websocket-driver's to [ "test" ]. This means that
the generated bundlerEnv wouldn't include websocket-driver unless the
test group was included, even though it's required by the default group.
This is arguably a bug in Bundix (websocket-driver's groups should
probably be [ "default" "test" ] or just [ "default" ]), but there's no
reason bundlerEnv should omit dependencies even given such an input --
it won't necessarily come from Bundix, and it would be good for
bundlerEnv to do the right thing.
To fix this, filterGemset is now a recursive function, that adds
dependencies of gems in the group to the filtered gemset until it
stabilises on the gems that match the required groups, and all of their
recursive dependencies.
102 lines
4.2 KiB
Nix
102 lines
4.2 KiB
Nix
{ ... }:
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rec {
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# Compute the fixed point of the given function `f`, which is usually an
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# attribute set that expects its final, non-recursive representation as an
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# argument:
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#
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# f = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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#
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# Nix evaluates this recursion until all references to `self` have been
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# resolved. At that point, the final result is returned and `f x = x` holds:
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#
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# nix-repl> fix f
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# { bar = "bar"; foo = "foo"; foobar = "foobar"; }
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#
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# Type: fix :: (a -> a) -> a
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#
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# See https://en.wikipedia.org/wiki/Fixed-point_combinator for further
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# details.
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fix = f: let x = f x; in x;
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# A variant of `fix` that records the original recursive attribute set in the
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# result. This is useful in combination with the `extends` function to
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# implement deep overriding. See pkgs/development/haskell-modules/default.nix
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# for a concrete example.
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fix' = f: let x = f x // { __unfix__ = f; }; in x;
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# Return the fixpoint that `f` converges to when called recursively, starting
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# with the input `x`.
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#
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# nix-repl> converge (x: x / 2) 16
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# 0
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converge = f: x:
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if (f x) == x
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then x
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else converge f (f x);
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# Modify the contents of an explicitly recursive attribute set in a way that
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# honors `self`-references. This is accomplished with a function
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#
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# g = self: super: { foo = super.foo + " + "; }
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#
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# that has access to the unmodified input (`super`) as well as the final
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# non-recursive representation of the attribute set (`self`). `extends`
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# differs from the native `//` operator insofar as that it's applied *before*
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# references to `self` are resolved:
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#
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# nix-repl> fix (extends g f)
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# { bar = "bar"; foo = "foo + "; foobar = "foo + bar"; }
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#
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# The name of the function is inspired by object-oriented inheritance, i.e.
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# think of it as an infix operator `g extends f` that mimics the syntax from
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# Java. It may seem counter-intuitive to have the "base class" as the second
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# argument, but it's nice this way if several uses of `extends` are cascaded.
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#
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# To get a better understanding how `extends` turns a function with a fix
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# point (the package set we start with) into a new function with a different fix
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# point (the desired packages set) lets just see, how `extends g f`
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# unfolds with `g` and `f` defined above:
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#
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# extends g f = self: let super = f self; in super // g self super;
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# = self: let super = { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }; in super // g self super
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# = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // g self { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; }
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# = self: { foo = "foo"; bar = "bar"; foobar = self.foo + self.bar; } // { foo = "foo" + " + "; }
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# = self: { foo = "foo + "; bar = "bar"; foobar = self.foo + self.bar; }
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#
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extends = f: rattrs: self: let super = rattrs self; in super // f self super;
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# Compose two extending functions of the type expected by 'extends'
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# into one where changes made in the first are available in the
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# 'super' of the second
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composeExtensions =
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f: g: self: super:
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let fApplied = f self super;
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super' = super // fApplied;
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in fApplied // g self super';
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# Create an overridable, recursive attribute set. For example:
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#
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# nix-repl> obj = makeExtensible (self: { })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; extend = «lambda»; }
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#
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# nix-repl> obj = obj.extend (self: super: { foo = "foo"; })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; extend = «lambda»; foo = "foo"; }
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#
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# nix-repl> obj = obj.extend (self: super: { foo = super.foo + " + "; bar = "bar"; foobar = self.foo + self.bar; })
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#
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# nix-repl> obj
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# { __unfix__ = «lambda»; bar = "bar"; extend = «lambda»; foo = "foo + "; foobar = "foo + bar"; }
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makeExtensible = makeExtensibleWithCustomName "extend";
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# Same as `makeExtensible` but the name of the extending attribute is
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# customized.
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makeExtensibleWithCustomName = extenderName: rattrs:
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fix' rattrs // {
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${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);
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};
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}
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