Commit eac25387 authored by Silvan Mosberger's avatar Silvan Mosberger
Browse files

lib.path.append: init 

This function can be used to append strings to Nix path values in a
safe way.
parent 5c4f6161

lib/path/default.nix

+47 −0
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ let 


  inherit (builtins)

    isString

    isPath

    split

    match

    ;
@@ -98,6 +99,52 @@ let 


in /* No rec! Add dependencies on this file at the top. */ {



  /* Append a subpath string to a path.



    Like `path + ("/" + string)` but safer, because it errors instead of returning potentially surprising results.

    More specifically, it checks that the first argument is a [path value type](https://nixos.org/manual/nix/stable/language/values.html#type-path"),

    and that the second argument is a valid subpath string (see `lib.path.subpath.isValid`).



    Type:

      append :: Path -> String -> Path



    Example:

      append /foo "bar/baz"

      => /foo/bar/baz



      # subpaths don't need to be normalised

      append /foo "./bar//baz/./"

      => /foo/bar/baz



      # can append to root directory

      append /. "foo/bar"

      => /foo/bar



      # first argument needs to be a path value type

      append "/foo" "bar"

      => <error>



      # second argument needs to be a valid subpath string

      append /foo /bar

      => <error>

      append /foo ""

      => <error>

      append /foo "/bar"

      => <error>

      append /foo "../bar"

      => <error>

  */

  append =

    # The absolute path to append to

    path:

    # The subpath string to append

    subpath:

    assert assertMsg (isPath path) ''

      lib.path.append: The first argument is of type ${builtins.typeOf path}, but a path was expected'';

    assert assertMsg (isValid subpath) ''

      lib.path.append: Second argument is not a valid subpath string:

          ${subpathInvalidReason subpath}'';

    path + ("/" + subpath);



  /* Whether a value is a valid subpath string.

lib/path/tests/unit.nix

+35 −1
Original line number Diff line number Diff line
@@ -3,9 +3,43 @@ 
{ libpath }:

let

  lib = import libpath;

  inherit (lib.path) subpath;

  inherit (lib.path) append subpath;



  cases = lib.runTests {

    # Test examples from the lib.path.append documentation

    testAppendExample1 = {

      expr = append /foo "bar/baz";

      expected = /foo/bar/baz;

    };

    testAppendExample2 = {

      expr = append /foo "./bar//baz/./";

      expected = /foo/bar/baz;

    };

    testAppendExample3 = {

      expr = append /. "foo/bar";

      expected = /foo/bar;

    };

    testAppendExample4 = {

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

      expected = false;

    };

    testAppendExample5 = {

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

      expected = false;

    };

    testAppendExample6 = {

      expr = (builtins.tryEval (append /foo "")).success;

      expected = false;

    };

    testAppendExample7 = {

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

      expected = false;

    };

    testAppendExample8 = {

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

      expected = false;

    };



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

    testSubpathIsValidExample1 = {

      expr = subpath.isValid null;