lib: init lists.uniqueStrings

lib/default.nix

@@ -287,6 +287,7 @@ let
         init
         crossLists
         unique
+        uniqueStrings
         allUnique
         intersectLists
         subtractLists

lib/lists.nix

@@ -11,7 +11,7 @@ let
     warn
     pipe
     ;
-  inherit (lib.attrsets) mapAttrs;
+  inherit (lib.attrsets) mapAttrs attrNames;
   inherit (lib) max;
 in
 rec {
@@ -1839,6 +1839,10 @@ rec {
   /**
     Remove duplicate elements from the `list`. O(n^2) complexity.
 
+    :::{.note}
+    If the list only contains strings and order is not important, the complexity can be reduced to O(n log n) by using [`lib.lists.uniqueStrings`](#function-library-lib.lists.uniqueStrings) instead.
+    :::
+
     # Inputs
 
     `list`
@@ -1864,6 +1868,43 @@ rec {
   */
   unique = foldl' (acc: e: if elem e acc then acc else acc ++ [ e ]) [ ];
 
+  /**
+    Removes duplicate strings from the `list`. O(n log n) complexity.
+
+    :::{.note}
+    Order is not preserved.
+
+    All elements of the list must be strings without context.
+
+    This function fails when the list contains a non-string element or a [string with context](https://nix.dev/manual/nix/latest/language/string-context.html).
+    In that case use [`lib.lists.unique`](#function-library-lib.lists.unique) instead.
+    :::
+
+    # Inputs
+
+    `list`
+
+    : List of strings
+
+    # Type
+
+    ```
+    uniqueStrings :: [ String ] -> [ String ]
+    ```
+
+    # Examples
+    :::{.example}
+    ## `lib.lists.uniqueStrings` usage example
+
+    ```nix
+    uniqueStrings [ "foo" "bar" "foo" ]
+    => [ "bar" "foo" ] # order is not preserved
+    ```
+
+    :::
+  */
+  uniqueStrings = list: attrNames (groupBy id list);
+
   /**
     Check if list contains only unique elements. O(n^2) complexity.
 

lib/tests/misc.nix

@@ -113,6 +113,7 @@ let
     toIntBase10
     toShellVars
     types
+    uniqueStrings
     updateManyAttrsByPath
     versions
     xor
@@ -1934,6 +1935,69 @@ runTests {
     expected = false;
   };
 
+  testUniqueStrings_empty = {
+    expr = uniqueStrings [ ];
+    expected = [ ];
+  };
+  testUniqueStrings_singles = {
+    expr = uniqueStrings [
+      "all"
+      "unique"
+      "already"
+    ];
+    expected = [
+      "all"
+      "already"
+      "unique"
+    ];
+  };
+  testUniqueStrings_allDuplicates = {
+    expr = uniqueStrings [
+      "dup"
+      "dup"
+      "dup"
+    ];
+    expected = [ "dup" ];
+  };
+  testUniqueStrings_some_duplicates = {
+    expr = uniqueStrings [
+      "foo"
+      "foo"
+      "bar"
+      "bar"
+      "baz"
+    ];
+    expected = [
+      "bar"
+      "baz"
+      "foo"
+    ];
+  };
+  testUniqueStrings_unicode = {
+    expr = uniqueStrings [
+      "café"
+      "@"
+      "#"
+      "@"
+      "#"
+      "$"
+      "😎"
+      "😎"
+      "🙃"
+      ""
+      ""
+    ];
+    expected = [
+      ""
+      "#"
+      "$"
+      "@"
+      "café"
+      "😎"
+      "🙃"
+    ];
+  };
+
   # ATTRSETS
 
   testConcatMapAttrs = {