Commit 11c20cd3 authored by Yueh-Shun Li's avatar Yueh-Shun Li
Browse files

lib.toExtension: init 



Co-authored-by: default avatarRobert Hensing <roberth@users.noreply.github.com>
parent 6749b1c4

lib/default.nix

+2 −1
Original line number Diff line number Diff line
@@ -79,7 +79,8 @@ let 
      fromHexString toHexString toBaseDigits inPureEvalMode isBool isInt pathExists

      genericClosure readFile;

    inherit (self.fixedPoints) fix fix' converge extends composeExtensions

      composeManyExtensions makeExtensible makeExtensibleWithCustomName;

      composeManyExtensions makeExtensible makeExtensibleWithCustomName

      toExtension;

    inherit (self.attrsets) attrByPath hasAttrByPath setAttrByPath

      getAttrFromPath attrVals attrNames attrValues getAttrs catAttrs filterAttrs

      filterAttrsRecursive foldlAttrs foldAttrs collect nameValuePair mapAttrs

lib/fixed-points.nix

+64 −0
Original line number Diff line number Diff line
@@ -438,4 +438,68 @@ rec { 
        ${extenderName} = f: makeExtensibleWithCustomName extenderName (extends f rattrs);

      }

    );



  /**

    Convert to an extending function (overlay).



    `toExtension` is the `toFunction` for extending functions (a.k.a. extensions or overlays).

    It converts a non-function or a single-argument function to an extending function,

    while returning a double-argument function as-is.



    That is, it takes one of `x`, `prev: x`, or `final: prev: x`,

    and returns `final: prev: x`, where `x` is not a function.



    This function is extracted from the implementation of

    the fixed-point arguments support of `stdenv.mkDerivation`.

    It bridges the gap between `<pkg>.overrideAttrs`

    before and after the overlay-style support,

    as well as `config.packageOverrides` and `config.overlays` in `pkgs`.



    # Inputs



    `f`

    : The function or non-function to convert to an extending function.



    # Type



    ```

    toExtension ::: (a | a -> a | a -> a -> a) -> a -> a -> a

    a = AttrSet & !Function

    ```



    # Examples

    :::{.example}

    ## `lib.fixedPoints.toExtension` usage example



    ```nix

    fix (final: { a = 0; c = final.a; })

    => { a = 0; c = 0; };



    fix (extends (toExtension { a = 1; b = 2; }) (final: { a = 0; c = final.a; }))

    => { a = 1; b = 2; c = 1; };



    fix (extends (toExtension (prev: { a = 1; b = prev.a; })) (final: { a = 0; c = final.a; }))

    => { a = 1; b = 0; c = 1; };



    fix (extends (toExtension (final: prev: { a = 1; b = prev.a; c = final.a + 1 })) (final: { a = 0; c = final.a; }))

    => { a = 1; b = 0; c = 2; };

    ```

    :::

  */

  toExtension =

    f:

    if lib.isFunction f then

      final: prev:

      let

        fPrev = f prev;

      in

      if lib.isFunction fPrev then

        # f is (final: prev: { ... })

        f final prev

      else

        # f is (prev: { ... })

        fPrev

    else

      # f is { ... }

      final: prev: f;

}

lib/tests/misc.nix

+17 −0
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ let 
    const

    escapeXML

    evalModules

    extends

    filter

    fix

    fold
@@ -102,6 +103,7 @@ let 
    take

    testAllTrue

    toBaseDigits

    toExtension

    toHexString

    fromHexString

    toInt
@@ -1239,6 +1241,21 @@ runTests { 
    expected = {a = "a";};

  };



  testToExtension = {

    expr = [

      (fix (final: { a = 0; c = final.a; }))

      (fix (extends (toExtension { a = 1; b = 2; }) (final: { a = 0; c = final.a; })))

      (fix (extends (toExtension (prev: { a = 1; b = prev.a; })) (final: { a = 0; c = final.a; })))

      (fix (extends (toExtension (final: prev: { a = 1; b = prev.a; c = final.a + 1; })) (final: { a = 0; c = final.a; })))

    ];

    expected = [

      { a = 0; c = 0; }

      { a = 1; b = 2; c = 1; }

      { a = 1; b = 0; c = 1; }

      { a = 1; b = 0; c = 2; }

    ];

  };



# GENERATORS

# these tests assume attributes are converted to lists

# in alphabetical order