[libcxx-commits] [libcxx] [libc++] Improve the tests for vector::erase (PR #116265)

[Louis Dionne via libcxx-commits]

================
@@ -200,5 +174,48 @@ int main(int, char**) {
   }
 #endif
 
+  // Real world example with std::string, mostly intended to test trivial relocation
+  {
+    std::vector<std::string> v;
+
+    // fill the vector with half short string and half long strings
+    std::string short_string = "short";
+    std::string long_string(256, 'x');
+    for (int i = 0; i != 10; ++i) {
+      v.push_back(i % 2 == 0 ? short_string : long_string);
+    }
+
+    std::vector<std::string> original = v;
+
+    auto it = v.erase(v.cbegin() + 2, v.cbegin() + 8);
+    assert(v.size() == 4);
+    assert(v[0] == original[0]);
+    assert(v[1] == original[1]);
+    assert(v[2] == original[8]);
+    assert(v[3] == original[9]);
+    assert(it == v.begin() + 2);
+  }
+
+  // Make sure we satisfy the complexity requirement in terms of the number of times the assignment
+  // operator is called.
+  {
+    Tracker tracker;
+    std::vector<TrackedAssignment> v;
+
+    // Set up the vector with 5 elements.
+    for (int i = 0; i != 5; ++i) {
+      v.emplace_back(&tracker);
+    }
+    assert(tracker.copy_assignments == 0);
+    assert(tracker.move_assignments == 0);
+
+    // Erase elements [1] and [2] from it. Elements [3] [4] should be shifted, so we should
+    // see 2 move assignments (and nothing else).
+    v.erase(v.begin() + 1, v.begin() + 3);
+    assert(v.size() == 3);
+    assert(tracker.copy_assignments == 0);
+    assert(tracker.move_assignments == 2);
----------------
ldionne wrote:

Whether this is actually mandated is currently being challenged. Since this is the behavior we currently have, I would like to leave this test in just so that we can explicitly see whether a change is changing that. After talking with some folks today at the WG21 meeting, I think it might be reasonable to change this behavior but that would be a different patch.

https://github.com/llvm/llvm-project/pull/116265