Export of internal Abseil changes

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35f516d528f4b53694ebe1f7debc023f1383cf4a by Shaindel Schwartz <shaindel@google.com>:

Internal change

PiperOrigin-RevId: 266967228

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40a0b91769133c48e3799a99f4dd2a7ce58bac91 by Derek Mauro <dmauro@google.com>:

Prevent absl::StrCat() and absl::StrAppend() from dereferencing std::string::end()

Fixes #374

PiperOrigin-RevId: 266447391
GitOrigin-RevId: 35f516d528f4b53694ebe1f7debc023f1383cf4a
Change-Id: I82e3a1bec5fa528db90a2f67dd3bc000e8dca8ab

absl/strings/str_cat.cc

@@ -99,7 +99,7 @@ std::string StrCat(const AlphaNum& a, const AlphaNum& b) {
   std::string result;
   absl::strings_internal::STLStringResizeUninitialized(&result,
                                                        a.size() + b.size());
-  char* const begin = &*result.begin();
+  char* const begin = &result[0];
   char* out = begin;
   out = Append(out, a);
   out = Append(out, b);
@@ -111,7 +111,7 @@ std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c) {
   std::string result;
   strings_internal::STLStringResizeUninitialized(
       &result, a.size() + b.size() + c.size());
-  char* const begin = &*result.begin();
+  char* const begin = &result[0];
   char* out = begin;
   out = Append(out, a);
   out = Append(out, b);
@@ -125,7 +125,7 @@ std::string StrCat(const AlphaNum& a, const AlphaNum& b, const AlphaNum& c,
   std::string result;
   strings_internal::STLStringResizeUninitialized(
       &result, a.size() + b.size() + c.size() + d.size());
-  char* const begin = &*result.begin();
+  char* const begin = &result[0];
   char* out = begin;
   out = Append(out, a);
   out = Append(out, b);
@@ -144,7 +144,7 @@ std::string CatPieces(std::initializer_list<absl::string_view> pieces) {
   for (const absl::string_view piece : pieces) total_size += piece.size();
   strings_internal::STLStringResizeUninitialized(&result, total_size);
 
-  char* const begin = &*result.begin();
+  char* const begin = &result[0];
   char* out = begin;
   for (const absl::string_view piece : pieces) {
     const size_t this_size = piece.size();
@@ -176,7 +176,7 @@ void AppendPieces(std::string* dest,
   }
   strings_internal::STLStringResizeUninitialized(dest, total_size);
 
-  char* const begin = &*dest->begin();
+  char* const begin = &(*dest)[0];
   char* out = begin + old_size;
   for (const absl::string_view piece : pieces) {
     const size_t this_size = piece.size();
@@ -201,7 +201,7 @@ void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b) {
   std::string::size_type old_size = dest->size();
   strings_internal::STLStringResizeUninitialized(
       dest, old_size + a.size() + b.size());
-  char* const begin = &*dest->begin();
+  char* const begin = &(*dest)[0];
   char* out = begin + old_size;
   out = Append(out, a);
   out = Append(out, b);
@@ -216,7 +216,7 @@ void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
   std::string::size_type old_size = dest->size();
   strings_internal::STLStringResizeUninitialized(
       dest, old_size + a.size() + b.size() + c.size());
-  char* const begin = &*dest->begin();
+  char* const begin = &(*dest)[0];
   char* out = begin + old_size;
   out = Append(out, a);
   out = Append(out, b);
@@ -233,7 +233,7 @@ void StrAppend(std::string* dest, const AlphaNum& a, const AlphaNum& b,
   std::string::size_type old_size = dest->size();
   strings_internal::STLStringResizeUninitialized(
       dest, old_size + a.size() + b.size() + c.size() + d.size());
-  char* const begin = &*dest->begin();
+  char* const begin = &(*dest)[0];
   char* out = begin + old_size;
   out = Append(out, a);
   out = Append(out, b);

absl/strings/str_cat_test.cc

@@ -195,6 +195,21 @@ TEST(StrCat, Basics) {
   EXPECT_EQ(result, "12333444455555666666777777788888888999999999");
 }
 
+TEST(StrCat, CornerCases) {
+  std::string result;
+
+  result = absl::StrCat("");  // NOLINT
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "");
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "", "");
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "", "", "");
+  EXPECT_EQ(result, "");
+  result = absl::StrCat("", "", "", "", "");
+  EXPECT_EQ(result, "");
+}
+
 // A minimal allocator that uses malloc().
 template <typename T>
 struct Mallocator {
@@ -433,10 +448,34 @@ TEST(StrAppend, Death) {
 }
 #endif  // GTEST_HAS_DEATH_TEST
 
-TEST(StrAppend, EmptyString) {
+TEST(StrAppend, CornerCases) {
-  std::string s = "";
+  std::string result;
-  absl::StrAppend(&s, s);
+  absl::StrAppend(&result, "");
-  EXPECT_EQ(s, "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "", "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "", "", "");
+  EXPECT_EQ(result, "");
+  absl::StrAppend(&result, "", "", "", "", "");
+  EXPECT_EQ(result, "");
+}
+
+TEST(StrAppend, CornerCasesNonEmptyAppend) {
+  for (std::string result : {"hello", "a std::string too long to fit in the SSO"}) {
+    const std::string expected = result;
+    absl::StrAppend(&result, "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "", "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "", "", "");
+    EXPECT_EQ(result, expected);
+    absl::StrAppend(&result, "", "", "", "", "");
+    EXPECT_EQ(result, expected);
+  }
 }
 
 template <typename IntType>