Export of internal Abseil changes

--
a78c34c705b15598ea00171d4ff8755e38fad863 by Derek Mauro <dmauro@google.com>:

Improve compiler support for ABSL_FALLTHROUGH_INTENDED

PiperOrigin-RevId: 370952333

--
aed0c26f1a2aac98e217ad1b44ce4a858780a223 by Martijn Vels <mvels@google.com>:

Add Cordz instrumentation for Flatten

PiperOrigin-RevId: 370815149

--
ff4a58d0109d39dc32ef7a5e5e669ca4e630c6d9 by Martijn Vels <mvels@google.com>:

Add Cordz instrumentation to RemovePrefix and RemoveSuffix

PiperOrigin-RevId: 370751602

--
40220a058b30ddd89c6e547591488d15342137dd by Martijn Vels <mvels@google.com>:

Add Cordz instrumentation to operator=(string_view)

PiperOrigin-RevId: 370737600

--
a2e49604f18b92e50b179b5477dfddb8f57538ca by Martijn Vels <mvels@google.com>:

Add cordz instrumentation for Subcord

PiperOrigin-RevId: 370724107

--
bcc3902e04fb4f14270aef00e18908e6a88474cd by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 370707219
GitOrigin-RevId: a78c34c705b15598ea00171d4ff8755e38fad863
Change-Id: I0270e536cbdeaf1f195199da822b314521de3b96

6 files changed, 192 insertions, 48 deletions

diff --git a/absl/strings/BUILD.bazel b/absl/strings/BUILD.bazel
index 68c71f0a..ae88f7bb 100644
--- a/absl/strings/BUILD.bazel
+++ b/absl/strings/BUILD.bazel
@@ -544,6 +544,7 @@ cc_library(
         ":cordz_sample_token",
         ":cordz_statistics",
         ":cordz_update_tracker",
+        ":strings",
         "//absl/base:config",
         "//absl/base:core_headers",
         "@com_google_googletest//:gtest",
diff --git a/absl/strings/CMakeLists.txt b/absl/strings/CMakeLists.txt
index 80ae2a60..8ebe91e6 100644
--- a/absl/strings/CMakeLists.txt
+++ b/absl/strings/CMakeLists.txt
@@ -852,6 +852,7 @@ absl_cc_library(
     absl::cordz_statistics
     absl::cordz_update_tracker
     absl::core_headers
+    absl::strings
   TESTONLY
 )
 
diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 15d17337..9262aee6 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -584,26 +584,35 @@ void Cord::Clear() {
 }
 
 Cord& Cord::operator=(absl::string_view src) {
+  auto constexpr method = CordzUpdateTracker::kAssignString;
   const char* data = src.data();
   size_t length = src.size();
   CordRep* tree = contents_.tree();
   if (length <= InlineRep::kMaxInline) {
-    // Embed into this->contents_
-    if (tree) CordzInfo::MaybeUntrackCord(contents_.cordz_info());
+    // Embed into this->contents_, which is somewhat subtle:
+    // - MaybeUntrackCord must be called before Unref(tree).
+    // - MaybeUntrackCord must be called before set_data() clobbers cordz_info.
+    // - set_data() must be called before Unref(tree) as it may reference tree.
+    if (tree != nullptr) CordzInfo::MaybeUntrackCord(contents_.cordz_info());
     contents_.set_data(data, length, true);
-    if (tree) CordRep::Unref(tree);
+    if (tree != nullptr) CordRep::Unref(tree);
     return *this;
   }
-  if (tree != nullptr && tree->tag >= FLAT &&
-      tree->flat()->Capacity() >= length && tree->refcount.IsOne()) {
-    // Copy in place if the existing FLAT node is reusable.
-    memmove(tree->flat()->Data(), data, length);
-    tree->length = length;
-    VerifyTree(tree);
-    return *this;
+  if (tree != nullptr) {
+    CordzUpdateScope scope(contents_.cordz_info(), method);
+    if (tree->tag >= FLAT && tree->flat()->Capacity() >= length &&
+        tree->refcount.IsOne()) {
+      // Copy in place if the existing FLAT node is reusable.
+      memmove(tree->flat()->Data(), data, length);
+      tree->length = length;
+      VerifyTree(tree);
+      return *this;
+    }
+    contents_.SetTree(NewTree(data, length, 0), scope);
+    CordRep::Unref(tree);
+  } else {
+    contents_.EmplaceTree(NewTree(data, length, 0), method);
   }
-  contents_.set_tree(NewTree(data, length, 0));
-  if (tree) CordRep::Unref(tree);
   return *this;
 }
 
@@ -893,12 +902,17 @@ void Cord::RemovePrefix(size_t n) {
   CordRep* tree = contents_.tree();
   if (tree == nullptr) {
     contents_.remove_prefix(n);
-  } else if (tree->tag == RING) {
-    contents_.replace_tree(CordRepRing::RemovePrefix(tree->ring(), n));
   } else {
-    CordRep* newrep = RemovePrefixFrom(tree, n);
-    CordRep::Unref(tree);
-    contents_.replace_tree(VerifyTree(newrep));
+    auto constexpr method = CordzUpdateTracker::kRemovePrefix;
+    CordzUpdateScope scope(contents_.cordz_info(), method);
+    if (tree->tag == RING) {
+      tree = CordRepRing::RemovePrefix(tree->ring(), n);
+    } else {
+      CordRep* newrep = RemovePrefixFrom(tree, n);
+      CordRep::Unref(tree);
+      tree = VerifyTree(newrep);
+    }
+    contents_.SetTreeOrEmpty(tree, scope);
   }
 }
 
@@ -909,12 +923,17 @@ void Cord::RemoveSuffix(size_t n) {
   CordRep* tree = contents_.tree();
   if (tree == nullptr) {
     contents_.reduce_size(n);
-  } else if (tree->tag == RING) {
-    contents_.replace_tree(CordRepRing::RemoveSuffix(tree->ring(), n));
   } else {
-    CordRep* newrep = RemoveSuffixFrom(tree, n);
-    CordRep::Unref(tree);
-    contents_.replace_tree(VerifyTree(newrep));
+    auto constexpr method = CordzUpdateTracker::kRemoveSuffix;
+    CordzUpdateScope scope(contents_.cordz_info(), method);
+    if (tree->tag == RING) {
+      tree = CordRepRing::RemoveSuffix(tree->ring(), n);
+    } else {
+      CordRep* newrep = RemoveSuffixFrom(tree, n);
+      CordRep::Unref(tree);
+      tree = VerifyTree(newrep);
+    }
+    contents_.SetTreeOrEmpty(tree, scope);
   }
 }
 
@@ -969,37 +988,51 @@ static CordRep* NewSubRange(CordRep* node, size_t pos, size_t n) {
   return results[0];
 }
 
+void Cord::CopyDataAtPosition(size_t pos, size_t new_size, char* dest) const {
+  assert(new_size <= cord_internal::kMaxInline);
+  assert(pos <= size());
+  assert(new_size <= size() - pos);
+  Cord::ChunkIterator it = chunk_begin();
+  it.AdvanceBytes(pos);
+  size_t remaining_size = new_size;
+  while (remaining_size > it->size()) {
+    cord_internal::SmallMemmove(dest, it->data(), it->size());
+    remaining_size -= it->size();
+    dest += it->size();
+    ++it;
+  }
+  cord_internal::SmallMemmove(dest, it->data(), remaining_size);
+}
+
 Cord Cord::Subcord(size_t pos, size_t new_size) const {
   Cord sub_cord;
   size_t length = size();
   if (pos > length) pos = length;
   if (new_size > length - pos) new_size = length - pos;
+  if (new_size == 0) return sub_cord;
+
   CordRep* tree = contents_.tree();
   if (tree == nullptr) {
     // sub_cord is newly constructed, no need to re-zero-out the tail of
     // contents_ memory.
     sub_cord.contents_.set_data(contents_.data() + pos, new_size, false);
-  } else if (new_size == 0) {
-    // We want to return empty subcord, so nothing to do.
-  } else if (new_size <= InlineRep::kMaxInline) {
-    Cord::ChunkIterator it = chunk_begin();
-    it.AdvanceBytes(pos);
-    char* dest = sub_cord.contents_.data_.as_chars();
-    size_t remaining_size = new_size;
-    while (remaining_size > it->size()) {
-      cord_internal::SmallMemmove(dest, it->data(), it->size());
-      remaining_size -= it->size();
-      dest += it->size();
-      ++it;
-    }
-    cord_internal::SmallMemmove(dest, it->data(), remaining_size);
+    return sub_cord;
+  }
+
+  if (new_size <= InlineRep::kMaxInline) {
+    CopyDataAtPosition(pos, new_size, sub_cord.contents_.data_.as_chars());
     sub_cord.contents_.set_inline_size(new_size);
-  } else if (tree->tag == RING) {
-    tree = CordRepRing::SubRing(CordRep::Ref(tree)->ring(), pos, new_size);
-    sub_cord.contents_.set_tree(tree);
+    return sub_cord;
+  }
+
+  if (tree->tag == RING) {
+    CordRepRing* ring = CordRep::Ref(tree)->ring();
+    tree = CordRepRing::SubRing(ring, pos, new_size);
   } else {
-    sub_cord.contents_.set_tree(NewSubRange(tree, pos, new_size));
+    tree = NewSubRange(tree, pos, new_size);
   }
+  sub_cord.contents_.EmplaceTree(tree, contents_.data_,
+                                 CordzUpdateTracker::kSubCord);
   return sub_cord;
 }
 
@@ -1676,6 +1709,7 @@ char Cord::operator[](size_t i) const {
 }
 
 absl::string_view Cord::FlattenSlowPath() {
+  assert(contents_.is_tree());
   size_t total_size = size();
   CordRep* new_rep;
   char* new_buffer;
@@ -1696,10 +1730,9 @@ absl::string_view Cord::FlattenSlowPath() {
                                             s.size());
         });
   }
-  if (CordRep* tree = contents_.tree()) {
-    CordRep::Unref(tree);
-  }
-  contents_.set_tree(new_rep);
+  CordzUpdateScope scope(contents_.cordz_info(), CordzUpdateTracker::kFlatten);
+  CordRep::Unref(contents_.as_tree());
+  contents_.SetTree(new_rep, scope);
   return absl::string_view(new_buffer, total_size);
 }
 
diff --git a/absl/strings/cord.h b/absl/strings/cord.h
index d5a13b34..d7b43247 100644
--- a/absl/strings/cord.h
+++ b/absl/strings/cord.h
@@ -692,6 +692,10 @@ class Cord {
   // called by Flatten() when the cord was not already flat.
   absl::string_view FlattenSlowPath();
 
+  // Copies `new_size` bytes starting at `pos` into `dest`. Requires at least
+  // `new_size` bytes to be available, and `new_size` to be <= kMaxInline.
+  void CopyDataAtPosition(size_t pos, size_t new_size, char* dest) const;
+
   // Actual cord contents are hidden inside the following simple
   // class so that we can isolate the bulk of cord.cc from changes
   // to the representation.
@@ -745,12 +749,21 @@ class Cord {
     // the CordzInfo instance is updated to reference the new `rep` value.
     void SetTree(CordRep* rep, const CordzUpdateScope& scope);
 
+    // Identical to SetTree(), except that `rep` is allowed to be null, in
+    // which case the current instance is reset to an empty value.
+    void SetTreeOrEmpty(CordRep* rep, const CordzUpdateScope& scope);
+
     // Sets the tree value for this instance, and randomly samples this cord.
     // This function disregards existing contents in `data_`, and should be
     // called when a Cord is 'promoted' from an 'uninitialized' or 'inlined'
     // value to a non-inlined (tree / ring) value.
     void EmplaceTree(CordRep* rep, MethodIdentifier method);
 
+    // Identical to EmplaceTree, except that it copies the parent stack from
+    // the provided `parent` data if the parent is sampled.
+    void EmplaceTree(CordRep* rep, const InlineData& parent,
+                     MethodIdentifier method);
+
     // Commits the change of a newly created, or updated `rep` root value into
     // this cord. `old_rep` indicates the old (inlined or tree) value of the
     // cord, and determines if the commit invokes SetTree() or EmplaceTree().
@@ -1071,6 +1084,12 @@ inline void Cord::InlineRep::EmplaceTree(CordRep* rep,
   CordzInfo::MaybeTrackCord(data_, method);
 }
 
+inline void Cord::InlineRep::EmplaceTree(CordRep* rep, const InlineData& parent,
+                                         MethodIdentifier method) {
+  data_.make_tree(rep);
+  CordzInfo::MaybeTrackCord(data_, parent, method);
+}
+
 inline void Cord::InlineRep::SetTree(CordRep* rep,
                                      const CordzUpdateScope& scope) {
   assert(rep);
@@ -1079,6 +1098,17 @@ inline void Cord::InlineRep::SetTree(CordRep* rep,
   scope.SetCordRep(rep);
 }
 
+inline void Cord::InlineRep::SetTreeOrEmpty(CordRep* rep,
+                                            const CordzUpdateScope& scope) {
+  assert(data_.is_tree());
+  if (rep) {
+    data_.set_tree(rep);
+  } else {
+    data_ = {};
+  }
+  scope.SetCordRep(rep);
+}
+
 inline void Cord::InlineRep::CommitTree(const CordRep* old_rep, CordRep* rep,
                                         const CordzUpdateScope& scope,
                                         MethodIdentifier method) {
diff --git a/absl/strings/cordz_test.cc b/absl/strings/cordz_test.cc
index b16e9686..84947cfd 100644
--- a/absl/strings/cordz_test.cc
+++ b/absl/strings/cordz_test.cc
@@ -52,6 +52,8 @@ inline void PrintTo(const Cord& cord, std::ostream* s) {
 
 namespace {
 
+auto constexpr kMaxInline = cord_internal::kMaxInline;
+
 // Returns a string_view value of the specified length
 // We do this to avoid 'consuming' large strings in Cord by default.
 absl::string_view MakeString(size_t size) {
@@ -139,6 +141,16 @@ TEST(CordzTest, MoveAssignCord) {
   EXPECT_THAT(cord, HasValidCordzInfoOf(Method::kConstructorString));
 }
 
+TEST_P(CordzUpdateTest, AssignSmallArray) {
+  cord() = MakeString(TestCordSize::kSmall);
+  EXPECT_THAT(cord(), HasValidCordzInfoOf(Method::kAssignString));
+}
+
+TEST_P(CordzUpdateTest, AssignInlinedArray) {
+  cord() = MakeString(TestCordSize::kInlined);
+  EXPECT_THAT(GetCordzInfoForTesting(cord()), Eq(nullptr));
+}
+
 TEST_P(CordzUpdateTest, AppendCord) {
   Cord src = UnsampledCord(MakeString(TestCordSize::kLarge));
   cord().Append(src);
@@ -166,6 +178,56 @@ TEST_P(CordzUpdateTest, AppendLargeArray) {
   EXPECT_THAT(cord(), HasValidCordzInfoOf(InitialOr(Method::kAppendString)));
 }
 
+TEST(CordzTest, RemovePrefix) {
+  CordzSamplingIntervalHelper sample_every(1);
+  Cord cord(MakeString(TestCordSize::kLarge));
+
+  // Half the cord
+  cord.RemovePrefix(cord.size() / 2);
+  EXPECT_THAT(cord, HasValidCordzInfoOf(Method::kConstructorString));
+  EXPECT_THAT(cord, CordzMethodCountEq(Method::kRemovePrefix, 1));
+
+  // TODO(mvels): RemovePrefix does not reset to inlined, except if empty?
+  cord.RemovePrefix(cord.size() - kMaxInline);
+  EXPECT_THAT(cord, HasValidCordzInfoOf(Method::kConstructorString));
+  EXPECT_THAT(cord, CordzMethodCountEq(Method::kRemovePrefix, 2));
+
+  cord.RemovePrefix(cord.size());
+  EXPECT_THAT(GetCordzInfoForTesting(cord), Eq(nullptr));
+}
+
+TEST(CordzTest, RemoveSuffix) {
+  CordzSamplingIntervalHelper sample_every(1);
+  Cord cord(MakeString(TestCordSize::kLarge));
+
+  // Half the cord
+  cord.RemoveSuffix(cord.size() / 2);
+  EXPECT_THAT(cord, HasValidCordzInfoOf(Method::kConstructorString));
+  EXPECT_THAT(cord, CordzMethodCountEq(Method::kRemoveSuffix, 1));
+
+  // TODO(mvels): RemoveSuffix does not reset to inlined, except if empty?
+  cord.RemoveSuffix(cord.size() - kMaxInline);
+  EXPECT_THAT(cord, HasValidCordzInfoOf(Method::kConstructorString));
+  EXPECT_THAT(cord, CordzMethodCountEq(Method::kRemoveSuffix, 2));
+
+  cord.RemoveSuffix(cord.size());
+  EXPECT_THAT(GetCordzInfoForTesting(cord), Eq(nullptr));
+}
+
+TEST(CordzTest, SubCord) {
+  CordzSamplingIntervalHelper sample_every{1};
+  Cord src(MakeString(TestCordSize::kLarge));
+
+  Cord cord1 = src.Subcord(10, src.size() / 2);
+  EXPECT_THAT(cord1, HasValidCordzInfoOf(Method::kSubCord));
+
+  Cord cord2 = src.Subcord(10, kMaxInline + 1);
+  EXPECT_THAT(cord2, HasValidCordzInfoOf(Method::kSubCord));
+
+  Cord cord3 = src.Subcord(10, kMaxInline);
+  EXPECT_THAT(GetCordzInfoForTesting(cord3), Eq(nullptr));
+}
+
 }  // namespace
 
 ABSL_NAMESPACE_END
diff --git a/absl/strings/cordz_test_helpers.h b/absl/strings/cordz_test_helpers.h
index d9573c97..e410eecf 100644
--- a/absl/strings/cordz_test_helpers.h
+++ b/absl/strings/cordz_test_helpers.h
@@ -27,6 +27,7 @@
 #include "absl/strings/internal/cordz_sample_token.h"
 #include "absl/strings/internal/cordz_statistics.h"
 #include "absl/strings/internal/cordz_update_tracker.h"
+#include "absl/strings/str_cat.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
@@ -34,7 +35,7 @@ ABSL_NAMESPACE_BEGIN
 // Returns the CordzInfo for the cord, or nullptr if the cord is not sampled.
 inline const cord_internal::CordzInfo* GetCordzInfoForTesting(
     const Cord& cord) {
-  if (cord.size() <= cord_internal::kMaxInline) return nullptr;
+  if (!cord.contents_.is_tree()) return nullptr;
   return cord.contents_.cordz_info();
 }
 
@@ -47,13 +48,11 @@ inline bool CordzInfoIsListed(const cord_internal::CordzInfo* cordz_info,
   return false;
 }
 
-// Matcher on Cord* that verifies all of:
+// Matcher on Cord that verifies all of:
 // - the cord is sampled
 // - the CordzInfo of the cord is listed / discoverable.
 // - the reported CordzStatistics match the cord's actual properties
 // - the cord has an (initial) UpdateTracker count of 1 for `method`
-// This matcher accepts a const Cord* to avoid having the matcher dump
-// copious amounts of cord data on failures.
 MATCHER_P(HasValidCordzInfoOf, method, "CordzInfo matches cord") {
   const cord_internal::CordzInfo* cord_info = GetCordzInfoForTesting(arg);
   if (cord_info == nullptr) {
@@ -78,6 +77,24 @@ MATCHER_P(HasValidCordzInfoOf, method, "CordzInfo matches cord") {
   return true;
 }
 
+// Matcher on Cord that verifies that the cord is sampled and that the CordzInfo
+// update tracker has 'method' with a call count of 'n'
+MATCHER_P2(CordzMethodCountEq, method, n,
+           absl::StrCat("CordzInfo method count equals ", n)) {
+  const cord_internal::CordzInfo* cord_info = GetCordzInfoForTesting(arg);
+  if (cord_info == nullptr) {
+    *result_listener << "cord is not sampled";
+    return false;
+  }
+  cord_internal::CordzStatistics stat = cord_info->GetCordzStatistics();
+  if (stat.update_tracker.Value(method) != n) {
+    *result_listener << "Expected method count " << n << " for " << method
+                     << ", found " << stat.update_tracker.Value(method);
+    return false;
+  }
+  return true;
+}
+
 // Cordz will only update with a new rate once the previously scheduled event
 // has fired. When we disable Cordz, a long delay takes place where we won't
 // consider profiling new Cords. CordzSampleIntervalHelper will burn through