ported from mozilla: Add UnorderedRemoveElement[s]At to nsTArray, r=froydnj

xpcom/tests/gtest/TestTArray.cpp

@@ -202,4 +202,124 @@ TEST(TArray, CopyOverlappingBackwards)
   }
 }
 
+TEST(TArray, UnorderedRemoveElements)
+{
+  // When removing an element from the end of the array, it can be removed in
+  // place, by destroying it and decrementing the length.
+  //
+  // [ 1, 2, 3 ] => [ 1, 2 ]
+  //         ^
+  {
+    nsTArray<int> array{ 1, 2, 3 };
+    array.UnorderedRemoveElementAt(2);
+
+    nsTArray<int> goal{ 1, 2 };
+    ASSERT_EQ(array, goal);
+  }
+
+  // When removing any other single element, it is removed by swapping it with
+  // the last element, and then decrementing the length as before.
+  //
+  // [ 1, 2, 3, 4, 5, 6 ]  => [ 1, 6, 3, 4, 5 ]
+  //      ^
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5, 6};
+    array.UnorderedRemoveElementAt(1);
+
+    nsTArray<int> goal{1, 6, 3, 4, 5};
+    ASSERT_EQ(array, goal);
+  }
+
+  // This method also supports efficiently removing a range of elements. If they
+  // are at the end, then they can all be removed like in the one element case.
+  //
+  // [ 1, 2, 3, 4, 5, 6 ] => [ 1, 2 ]
+  //         ^--------^
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5, 6};
+    array.UnorderedRemoveElementsAt(2, 4);
+
+    nsTArray<int> goal{1, 2};
+    ASSERT_EQ(array, goal);
+  }
+
+  // If more elements are removed than exist after the removed section, the
+  // remaining elements will be shifted down like in a normal removal.
+  //
+  // [ 1, 2, 3, 4, 5, 6, 7, 8 ] => [ 1, 2, 7, 8 ]
+  //         ^--------^
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5, 6, 7, 8};
+    array.UnorderedRemoveElementsAt(2, 4);
+
+    nsTArray<int> goal{1, 2, 7, 8};
+    ASSERT_EQ(array, goal);
+  }
+
+  // And if fewer elements are removed than exist after the removed section,
+  // elements will be moved from the end of the array to fill the vacated space.
+  //
+  // [ 1, 2, 3, 4, 5, 6, 7, 8 ] => [ 1, 7, 8, 4, 5, 6 ]
+  //      ^--^
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5, 6, 7, 8};
+    array.UnorderedRemoveElementsAt(1, 2);
+
+    nsTArray<int> goal{1, 7, 8, 4, 5, 6};
+    ASSERT_EQ(array, goal);
+  }
+
+  // We should do the right thing if we drain the entire array.
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5};
+    array.UnorderedRemoveElementsAt(0, 5);
+
+    nsTArray<int> goal{};
+    ASSERT_EQ(array, goal);
+  }
+
+  {
+    nsTArray<int> array{1};
+    array.UnorderedRemoveElementAt(0);
+
+    nsTArray<int> goal{};
+    ASSERT_EQ(array, goal);
+  }
+
+  // We should do the right thing if we remove the same number of elements that
+  // we have remaining.
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5, 6};
+    array.UnorderedRemoveElementsAt(2, 2);
+
+    nsTArray<int> goal{1, 2, 5, 6};
+    ASSERT_EQ(array, goal);
+  }
+
+  {
+    nsTArray<int> array{1, 2, 3};
+    array.UnorderedRemoveElementAt(1);
+
+    nsTArray<int> goal{1, 3};
+    ASSERT_EQ(array, goal);
+  }
+
+  // We should be able to remove elements from the front without issue.
+  {
+    nsTArray<int> array{1, 2, 3, 4, 5, 6};
+    array.UnorderedRemoveElementsAt(0, 2);
+
+    nsTArray<int> goal{5, 6, 3, 4};
+    ASSERT_EQ(array, goal);
+  }
+
+  {
+    nsTArray<int> array{1, 2, 3, 4};
+    array.UnorderedRemoveElementAt(0);
+
+    nsTArray<int> goal{4, 2, 3};
+    ASSERT_EQ(array, goal);
+  }
+}
+
 } // namespace TestTArray