[ADT] Use adl_begin in make_first_range and make_second_range

llvm/include/llvm/ADT/STLExtras.h

@@ -1434,7 +1434,7 @@ template <typename EltTy, typename FirstTy> class first_or_second_type {
 
 /// Given a container of pairs, return a range over the first elements.
 template <typename ContainerTy> auto make_first_range(ContainerTy &&c) {
-  using EltTy = decltype((*std::begin(c)));
+  using EltTy = decltype(*adl_begin(c));
   return llvm::map_range(std::forward<ContainerTy>(c),
                          [](EltTy elt) -> typename detail::first_or_second_type<
                                            EltTy, decltype((elt.first))>::type {
@@ -1444,7 +1444,7 @@ template <typename ContainerTy> auto make_first_range(ContainerTy &&c) {
 
 /// Given a container of pairs, return a range over the second elements.
 template <typename ContainerTy> auto make_second_range(ContainerTy &&c) {
-  using EltTy = decltype((*std::begin(c)));
+  using EltTy = decltype(*adl_begin(c));
   return llvm::map_range(
       std::forward<ContainerTy>(c),
       [](EltTy elt) ->

llvm/unittests/ADT/STLExtrasTest.cpp

@@ -428,9 +428,17 @@ struct List {
 std::list<int>::const_iterator begin(const List &list) {
   return list.data.begin();
 }
-
 std::list<int>::const_iterator end(const List &list) { return list.data.end(); }
 
+struct Pairs {
+  std::vector<std::pair<std::string, int>> data;
+  using const_iterator =
+      std::vector<std::pair<std::string, int>>::const_iterator;
+};
+
+Pairs::const_iterator begin(const Pairs &p) { return p.data.begin(); }
+Pairs::const_iterator end(const Pairs &p) { return p.data.end(); }
+
 struct requires_move {};
 int *begin(requires_move &&) { return nullptr; }
 int *end(requires_move &&) { return nullptr; }
@@ -524,6 +532,15 @@ TEST(STLExtrasTest, ConcatRangeADL) {
   EXPECT_THAT(concat<const int>(S0, S1), ElementsAre(1, 2, 3, 4));
 }
 
+TEST(STLExtrasTest, MakeFirstSecondRangeADL) {
+  // Make sure that we use the `begin`/`end` functions from `some_namespace`,
+  // using ADL.
+  some_namespace::Pairs Pairs;
+  Pairs.data = {{"foo", 1}, {"bar", 2}};
+  EXPECT_THAT(make_first_range(Pairs), ElementsAre("foo", "bar"));
+  EXPECT_THAT(make_second_range(Pairs), ElementsAre(1, 2));
+}
+
 template <typename T> struct Iterator {
   int i = 0;
   T operator*() const { return i; }