3 files changed, 108 insertions, 23 deletions
diff --git a/absl/container/BUILD.bazel b/absl/container/BUILD.bazel
index ee017431c88b..7d550cb16c5a 100644
--- a/absl/container/BUILD.bazel
+++ b/absl/container/BUILD.bazel
@@ -112,6 +112,9 @@ cc_library(
     srcs = ["internal/test_instance_tracker.cc"],
     hdrs = ["internal/test_instance_tracker.h"],
     copts = ABSL_DEFAULT_COPTS,
+    visibility = [
+        "//absl:__subpackages__",
+    ],
 )
 
 cc_test(
diff --git a/absl/container/inlined_vector.h b/absl/container/inlined_vector.h
index f68ca5074149..e0bb900cbb66 100644
--- a/absl/container/inlined_vector.h
+++ b/absl/container/inlined_vector.h
@@ -82,7 +82,8 @@ class InlinedVector {
   using reverse_iterator = std::reverse_iterator<iterator>;
   using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
-  InlinedVector() noexcept(noexcept(allocator_type()))
+  InlinedVector() noexcept(
+      std::is_nothrow_default_constructible<allocator_type>::value)
       : allocator_and_tag_(allocator_type()) {}
 
   explicit InlinedVector(const allocator_type& alloc) noexcept
@@ -148,6 +149,9 @@ class InlinedVector {
   ~InlinedVector() { clear(); }
 
   InlinedVector& operator=(const InlinedVector& v) {
+    if (this == &v) {
+      return *this;
+    }
     // Optimized to avoid reallocation.
     // Prefer reassignment to copy construction for elements.
     if (size() < v.size()) {  // grow
@@ -680,6 +684,8 @@ class InlinedVector {
   // portion and the start of the uninitialized portion of the created gap.
   // The number of initialized spots is pair.second - pair.first;
   // the number of raw spots is n - (pair.second - pair.first).
+  //
+  // Updates the size of the InlinedVector internally.
   std::pair<iterator, iterator> ShiftRight(const_iterator position,
                                            size_type n);
 
@@ -1013,28 +1019,19 @@ typename InlinedVector<T, N, A>::iterator InlinedVector<T, N, A>::emplace(
     emplace_back(std::forward<Args>(args)...);
     return end() - 1;
   }
-  size_type s = size();
-  size_type idx = std::distance(cbegin(), position);
-  if (s == capacity()) {
-    EnlargeBy(1);
-  }
-  assert(s < capacity());
-  iterator pos = begin() + idx;  // Set 'pos' to a post-enlarge iterator.
 
-  pointer space;
-  if (allocated()) {
-    tag().set_allocated_size(s + 1);
-    space = allocated_space();
+  T new_t = T(std::forward<Args>(args)...);
+
+  auto range = ShiftRight(position, 1);
+  if (range.first == range.second) {
+    // constructing into uninitialized memory
+    Construct(range.first, std::move(new_t));
   } else {
-    tag().set_inline_size(s + 1);
-    space = inlined_space();
+    // assigning into moved-from object
+    *range.first = T(std::move(new_t));
   }
-  Construct(space + s, std::move(space[s - 1]));
-  std::move_backward(pos, space + s - 1, space + s);
-  Destroy(pos, pos + 1);
-  Construct(pos, std::forward<Args>(args)...);
 
-  return pos;
+  return range.first;
 }
 
 template <typename T, size_t N, typename A>
@@ -1219,6 +1216,7 @@ auto InlinedVector<T, N, A>::ShiftRight(const_iterator position, size_type n)
     start_used = pos;
     start_raw = pos + new_elements_in_used_space;
   }
+  tag().add_size(n);
   return std::make_pair(start_used, start_raw);
 }
 
@@ -1297,10 +1295,12 @@ auto InlinedVector<T, N, A>::InsertWithCount(const_iterator position,
     -> iterator {
   assert(position >= begin() && position <= end());
   if (n == 0) return const_cast<iterator>(position);
+
+  value_type copy = v;
   std::pair<iterator, iterator> it_pair = ShiftRight(position, n);
-  std::fill(it_pair.first, it_pair.second, v);
-  UninitializedFill(it_pair.second, it_pair.first + n, v);
-  tag().add_size(n);
+  std::fill(it_pair.first, it_pair.second, copy);
+  UninitializedFill(it_pair.second, it_pair.first + n, copy);
+
   return it_pair.first;
 }
 
@@ -1336,7 +1336,6 @@ auto InlinedVector<T, N, A>::InsertWithRange(const_iterator position,
   ForwardIter open_spot = std::next(first, used_spots);
   std::copy(first, open_spot, it_pair.first);
   UninitializedCopy(open_spot, last, it_pair.second);
-  tag().add_size(n);
   return it_pair.first;
 }
 
diff --git a/absl/container/inlined_vector_test.cc b/absl/container/inlined_vector_test.cc
index c559a9a1fcba..055bca983cac 100644
--- a/absl/container/inlined_vector_test.cc
+++ b/absl/container/inlined_vector_test.cc
@@ -14,6 +14,7 @@
 
 #include "absl/container/inlined_vector.h"
 
+#include <algorithm>
 #include <forward_list>
 #include <list>
 #include <memory>
@@ -569,6 +570,16 @@ TEST(IntVec, CopyConstructorAndAssignment) {
   }
 }
 
+TEST(IntVec, AliasingCopyAssignment) {
+  for (int len = 0; len < 20; ++len) {
+    IntVec original;
+    Fill(&original, len);
+    IntVec dup = original;
+    dup = dup;
+    EXPECT_EQ(dup, original);
+  }
+}
+
 TEST(IntVec, MoveConstructorAndAssignment) {
   for (int len = 0; len < 20; len++) {
     IntVec v_in;
@@ -606,6 +617,78 @@ TEST(IntVec, MoveConstructorAndAssignment) {
   }
 }
 
+class NotTriviallyDestructible {
+ public:
+  NotTriviallyDestructible() : p_(new int(1)) {}
+  explicit NotTriviallyDestructible(int i) : p_(new int(i)) {}
+
+  NotTriviallyDestructible(const NotTriviallyDestructible& other)
+      : p_(new int(*other.p_)) {}
+
+  NotTriviallyDestructible& operator=(const NotTriviallyDestructible& other) {
+    p_ = absl::make_unique<int>(*other.p_);
+    return *this;
+  }
+
+  bool operator==(const NotTriviallyDestructible& other) const {
+    return *p_ == *other.p_;
+  }
+
+ private:
+  std::unique_ptr<int> p_;
+};
+
+TEST(AliasingTest, Emplace) {
+  for (int i = 2; i < 20; ++i) {
+    absl::InlinedVector<NotTriviallyDestructible, 10> vec;
+    for (int j = 0; j < i; ++j) {
+      vec.push_back(NotTriviallyDestructible(j));
+    }
+    vec.emplace(vec.begin(), vec[0]);
+    EXPECT_EQ(vec[0], vec[1]);
+    vec.emplace(vec.begin() + i / 2, vec[i / 2]);
+    EXPECT_EQ(vec[i / 2], vec[i / 2 + 1]);
+    vec.emplace(vec.end() - 1, vec.back());
+    EXPECT_EQ(vec[vec.size() - 2], vec.back());
+  }
+}
+
+TEST(AliasingTest, InsertWithCount) {
+  for (int i = 1; i < 20; ++i) {
+    absl::InlinedVector<NotTriviallyDestructible, 10> vec;
+    for (int j = 0; j < i; ++j) {
+      vec.push_back(NotTriviallyDestructible(j));
+    }
+    for (int n = 0; n < 5; ++n) {
+      // We use back where we can because it's guaranteed to become invalidated
+      vec.insert(vec.begin(), n, vec.back());
+      auto b = vec.begin();
+      EXPECT_TRUE(
+          std::all_of(b, b + n, [&vec](const NotTriviallyDestructible& x) {
+            return x == vec.back();
+          }));
+
+      auto m_idx = vec.size() / 2;
+      vec.insert(vec.begin() + m_idx, n, vec.back());
+      auto m = vec.begin() + m_idx;
+      EXPECT_TRUE(
+          std::all_of(m, m + n, [&vec](const NotTriviallyDestructible& x) {
+            return x == vec.back();
+          }));
+
+      // We want distinct values so the equality test is meaningful,
+      // vec[vec.size() - 1] is also almost always invalidated.
+      auto old_e = vec.size() - 1;
+      auto val = vec[old_e];
+      vec.insert(vec.end(), n, vec[old_e]);
+      auto e = vec.begin() + old_e;
+      EXPECT_TRUE(std::all_of(
+          e, e + n,
+          [&val](const NotTriviallyDestructible& x) { return x == val; }));
+    }
+  }
+}
+
 TEST(OverheadTest, Storage) {
   // Check for size overhead.
   // In particular, ensure that std::allocator doesn't cost anything to store.