Implement correct move constructor and assignment for absl::strings_internal::OStringStream, and mark that class final.

This should be explicit per https://google.github.io/styleguide/cppguide.html#Copyable_Movable_Types, and is currently hard to infer due to multiple inheritance.

PiperOrigin-RevId: 474311032
Change-Id: I72d7adcb9f7a991c19c26bc7083a4df31de5da49

1 files changed, 41 insertions, 12 deletions

diff --git a/absl/strings/internal/ostringstream_test.cc b/absl/strings/internal/ostringstream_test.cc
index 2879e50e..ef3ad573 100644
--- a/absl/strings/internal/ostringstream_test.cc
+++ b/absl/strings/internal/ostringstream_test.cc
@@ -14,10 +14,12 @@
 
 #include "absl/strings/internal/ostringstream.h"
 
+#include <ios>
 #include <memory>
 #include <ostream>
 #include <string>
 #include <type_traits>
+#include <utility>
 
 #include "gtest/gtest.h"
 
@@ -29,24 +31,51 @@ TEST(OStringStream, IsOStream) {
       "");
 }
 
-TEST(OStringStream, ConstructDestroy) {
+TEST(OStringStream, ConstructNullptr) {
+  absl::strings_internal::OStringStream strm(nullptr);
+  EXPECT_EQ(nullptr, strm.str());
+}
+
+TEST(OStringStream, ConstructStr) {
+  std::string s = "abc";
   {
-    absl::strings_internal::OStringStream strm(nullptr);
-    EXPECT_EQ(nullptr, strm.str());
+    absl::strings_internal::OStringStream strm(&s);
+    EXPECT_EQ(&s, strm.str());
   }
+  EXPECT_EQ("abc", s);
+}
+
+TEST(OStringStream, Destroy) {
+  std::unique_ptr<std::string> s(new std::string);
+  absl::strings_internal::OStringStream strm(s.get());
+  s.reset();
+}
+
+TEST(OStringStream, MoveConstruct) {
+  std::string s = "abc";
   {
-    std::string s = "abc";
-    {
-      absl::strings_internal::OStringStream strm(&s);
-      EXPECT_EQ(&s, strm.str());
-    }
-    EXPECT_EQ("abc", s);
+    absl::strings_internal::OStringStream strm1(&s);
+    strm1 << std::hex << 16;
+    EXPECT_EQ(&s, strm1.str());
+    absl::strings_internal::OStringStream strm2(std::move(strm1));
+    strm2 << 16;  // We should still be in base 16.
+    EXPECT_EQ(&s, strm2.str());
   }
+  EXPECT_EQ("abc1010", s);
+}
+
+TEST(OStringStream, MoveAssign) {
+  std::string s = "abc";
   {
-    std::unique_ptr<std::string> s(new std::string);
-    absl::strings_internal::OStringStream strm(s.get());
-    s.reset();
+    absl::strings_internal::OStringStream strm1(&s);
+    strm1 << std::hex << 16;
+    EXPECT_EQ(&s, strm1.str());
+    absl::strings_internal::OStringStream strm2(nullptr);
+    strm2 = std::move(strm1);
+    strm2 << 16;  // We should still be in base 16.
+    EXPECT_EQ(&s, strm2.str());
   }
+  EXPECT_EQ("abc1010", s);
 }
 
 TEST(OStringStream, Str) {