Commit 6626d8cc authored by Silvan Mosberger's avatar Silvan Mosberger
Browse files

lib.path.removePrefix: init

parent 7a49b67e

lib/path/default.nix

+53 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ let 
    concatMap

    foldl'

    take

    drop

    ;



  inherit (lib.strings)
@@ -217,6 +218,58 @@ in /* No rec! Add dependencies on this file at the top. */ { 
              second argument: "${toString path2}" with root "${toString path2Deconstructed.root}"'';

        take (length path1Deconstructed.components) path2Deconstructed.components == path1Deconstructed.components;



  /*

  Remove the first path as a component-wise prefix from the second path.

  The result is a normalised subpath string, see `lib.path.subpath.normalise`.



  Laws:



  - Inverts `append` for normalised subpaths:



        removePrefix p (append p s) == subpath.normalise s



  Type:

    removePrefix :: Path -> Path -> String



  Example:

    removePrefix /foo /foo/bar/baz

    => "./bar/baz"

    removePrefix /foo /foo

    => "./."

    removePrefix /foo/bar /foo

    => <error>

    removePrefix /. /foo

    => "./foo"

  */

  removePrefix =

    path1:

    assert assertMsg

      (isPath path1)

      "lib.path.removePrefix: First argument is of type ${typeOf path1}, but a path was expected.";

    let

      path1Deconstructed = deconstructPath path1;

      path1Length = length path1Deconstructed.components;

    in

      path2:

      assert assertMsg

        (isPath path2)

        "lib.path.removePrefix: Second argument is of type ${typeOf path2}, but a path was expected.";

      let

        path2Deconstructed = deconstructPath path2;

        success = take path1Length path2Deconstructed.components == path1Deconstructed.components;

        components =

          if success then

            drop path1Length path2Deconstructed.components

          else

            throw ''

              lib.path.removePrefix: The first path argument "${toString path1}" is not a component-wise prefix of the second path argument "${toString path2}".'';

      in

        assert assertMsg

        (path1Deconstructed.root == path2Deconstructed.root) ''

          lib.path.removePrefix: Filesystem roots must be the same for both paths, but paths with different roots were given:

              first argument: "${toString path1}" with root "${toString path1Deconstructed.root}"

              second argument: "${toString path2}" with root "${toString path2Deconstructed.root}"'';

        joinRelPath components;



  /* Whether a value is a valid subpath string.

lib/path/tests/unit.nix

+18 −1
Original line number Diff line number Diff line
@@ -3,7 +3,7 @@ 
{ libpath }:

let

  lib = import libpath;

  inherit (lib.path) hasPrefix append subpath;

  inherit (lib.path) hasPrefix removePrefix append subpath;



  cases = lib.runTests {

    # Test examples from the lib.path.append documentation
@@ -57,6 +57,23 @@ let 
      expected = true;

    };



    testRemovePrefixExample1 = {

      expr = removePrefix /foo /foo/bar/baz;

      expected = "./bar/baz";

    };

    testRemovePrefixExample2 = {

      expr = removePrefix /foo /foo;

      expected = "./.";

    };

    testRemovePrefixExample3 = {

      expr = (builtins.tryEval (removePrefix /foo/bar /foo)).success;

      expected = false;

    };

    testRemovePrefixExample4 = {

      expr = removePrefix /. /foo;

      expected = "./foo";

    };



    # Test examples from the lib.path.subpath.isValid documentation

    testSubpathIsValidExample1 = {

      expr = subpath.isValid null;