[MapVector] Introduce {keys,values} iterators (llvm#169675)

Similar to DenseMap::{keys,values}, introduce MapVector::{keys,values}.

Author: artagnon

llvm/include/llvm/ADT/MapVector.h

@@ -99,6 +99,11 @@ class MapVector {
     return try_emplace_impl(Key).first->second;
   }
 
+  [[nodiscard]] auto keys() { return make_first_range(Vector); }
+  [[nodiscard]] auto keys() const { return make_first_range(Vector); }
+  [[nodiscard]] auto values() { return make_second_range(Vector); }
+  [[nodiscard]] auto values() const { return make_second_range(Vector); }
+
   // Returns a copy of the value.  Only allowed if ValueT is copyable.
   [[nodiscard]] ValueT lookup(const KeyT &Key) const {
     static_assert(std::is_copy_constructible_v<ValueT>,

llvm/unittests/ADT/MapVectorTest.cpp

@@ -307,6 +307,24 @@ TEST(MapVectorTest, AtTest) {
   EXPECT_EQ(ConstMV.at(1), 12);
 }
 
+TEST(MapVectorTest, KeysValuesIterator) {
+  MapVector<int, int> MV;
+
+  MV.insert(std::make_pair(1, 11));
+  MV.insert(std::make_pair(2, 12));
+  MV.insert(std::make_pair(3, 13));
+  MV.insert(std::make_pair(4, 14));
+  MV.insert(std::make_pair(5, 15));
+  MV.insert(std::make_pair(6, 16));
+
+  EXPECT_THAT(MV.keys(), testing::ElementsAre(1, 2, 3, 4, 5, 6));
+  EXPECT_THAT(MV.values(), testing::ElementsAre(11, 12, 13, 14, 15, 16));
+
+  const MapVector<int, int> &ConstMV = MV;
+  EXPECT_THAT(ConstMV.keys(), testing::ElementsAre(1, 2, 3, 4, 5, 6));
+  EXPECT_THAT(ConstMV.values(), testing::ElementsAre(11, 12, 13, 14, 15, 16));
+}
+
 template <class IntType> struct MapVectorMappedTypeTest : ::testing::Test {
   using int_type = IntType;
 };