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

lib.toExtension: init

parent 6749b1c4
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+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
+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;
}
+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