[libc++][ranges] Fix the return value of `{copy,move}_backward`.

The return value for both of these algorithms is specified as
```
`{last, result - N}` for the overloads in namespace `ranges`.
```
But the current implementation instead returns `{first, result - N}`.

Also add both algorithms to the relevant "robust" tests.

Differential Revision: https://reviews.llvm.org/D130968

(cherry picked from commit f537a01d3989d37aafc050a92c74e69d35381f8c)

1 files changed, 9 insertions, 9 deletions

diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy_backward.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy_backward.pass.cpp
index b75eced30b79..d99fa4888430 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy_backward.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy_backward.pass.cpp
@@ -65,7 +65,7 @@ constexpr void test_iterators() {
       std::same_as<std::ranges::in_out_result<In, Out>> auto ret =
         std::ranges::copy_backward(In(in.data()), Sent(In(in.data() + in.size())), Out(out.data() + out.size()));
       assert(in == out);
-      assert(base(ret.in) == in.data());
+      assert(base(ret.in) == in.data() + in.size());
       assert(base(ret.out) == out.data());
     }
     {
@@ -75,7 +75,7 @@ constexpr void test_iterators() {
       std::same_as<std::ranges::in_out_result<In, Out>> auto ret =
           std::ranges::copy_backward(range, Out(out.data() + out.size()));
       assert(in == out);
-      assert(base(ret.in) == in.data());
+      assert(base(ret.in) == in.data() + in.size());
       assert(base(ret.out) == out.data());
     }
   }
@@ -86,7 +86,7 @@ constexpr void test_iterators() {
       std::array<int, 0> out;
       auto ret =
           std::ranges::copy_backward(In(in.data()), Sent(In(in.data() + in.size())), Out(out.data() + out.size()));
-      assert(base(ret.in) == in.data());
+      assert(base(ret.in) == in.data() + in.size());
       assert(base(ret.out) == out.data());
     }
     {
@@ -94,7 +94,7 @@ constexpr void test_iterators() {
       std::array<int, 0> out;
       auto range = std::ranges::subrange(In(in.data()), Sent(In(in.data() + in.size())));
       auto ret = std::ranges::copy_backward(range, Out(out.data()));
-      assert(base(ret.in) == in.data());
+      assert(base(ret.in) == in.data() + in.size());
       assert(base(ret.out) == out.data());
     }
   }
@@ -143,7 +143,7 @@ constexpr bool test() {
     std::array<int, 4> out;
     std::same_as<std::ranges::in_out_result<int*, int*>> auto ret =
         std::ranges::copy_backward(std::views::all(in), out.data() + out.size());
-    assert(ret.in == in.data());
+    assert(ret.in == in.data() + in.size());
     assert(ret.out == out.data());
     assert(in == out);
   }
@@ -163,7 +163,7 @@ constexpr bool test() {
       std::array<CopyOnce, 4> in {};
       std::array<CopyOnce, 4> out {};
       auto ret = std::ranges::copy_backward(in.begin(), in.end(), out.end());
-      assert(ret.in == in.begin());
+      assert(ret.in == in.end());
       assert(ret.out == out.begin());
       assert(std::all_of(out.begin(), out.end(), [](const auto& e) { return e.copied; }));
     }
@@ -171,7 +171,7 @@ constexpr bool test() {
       std::array<CopyOnce, 4> in {};
       std::array<CopyOnce, 4> out {};
       auto ret = std::ranges::copy_backward(in, out.end());
-      assert(ret.in == in.begin());
+      assert(ret.in == in.end());
       assert(ret.out == out.begin());
       assert(std::all_of(out.begin(), out.end(), [](const auto& e) { return e.copied; }));
     }
@@ -196,7 +196,7 @@ constexpr bool test() {
       out[2].next = &out[1];
       out[2].canCopy = true;
       auto ret = std::ranges::copy_backward(in, out.end());
-      assert(ret.in == in.begin());
+      assert(ret.in == in.end());
       assert(ret.out == out.begin());
       assert(out[0].canCopy);
       assert(out[1].canCopy);
@@ -209,7 +209,7 @@ constexpr bool test() {
       out[2].next = &out[1];
       out[2].canCopy = true;
       auto ret = std::ranges::copy_backward(in.begin(), in.end(), out.end());
-      assert(ret.in == in.begin());
+      assert(ret.in == in.end());
       assert(ret.out == out.begin());
       assert(out[0].canCopy);
       assert(out[1].canCopy);