Three-way comparison spaceship <=> operators for Cord.

This is portable because cord already has `operator<` etc., which will be unaffected. This just allows C++ >= 20 users to explicitly call `operator<=>`.

PiperOrigin-RevId: 646951415
Change-Id: I1432e224bd5dc09b99d56a1d27e95078463adf45

1 files changed, 26 insertions, 0 deletions

diff --git a/absl/strings/cord_test.cc b/absl/strings/cord_test.cc
index c4a7288a..eaf6d719 100644
--- a/absl/strings/cord_test.cc
+++ b/absl/strings/cord_test.cc
@@ -60,6 +60,7 @@
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
+#include "absl/types/compare.h"
 #include "absl/types/optional.h"
 
 // convenience local constants
@@ -3283,6 +3284,31 @@ TEST(CrcCordTest, ChecksummedEmptyCordEstimateMemoryUsage) {
   EXPECT_NE(cord.EstimatedMemoryUsage(), 0);
 }
 
+TEST(CordThreeWayComparisonTest, CompareCords) {
+#ifndef __cpp_impl_three_way_comparison
+  GTEST_SKIP() << "C++20 three-way <=> comparison not supported";
+#else
+  EXPECT_EQ(absl::Cord("a") <=> absl::Cord("a"), std::strong_ordering::equal);
+  EXPECT_EQ(absl::Cord("aaaa") <=> absl::Cord("aaab"),
+            std::strong_ordering::less);
+  EXPECT_EQ(absl::Cord("baaa") <=> absl::Cord("a"),
+            std::strong_ordering::greater);
+#endif
+}
+
+TEST(CordThreeWayComparisonTest, CompareCordsAndStringViews) {
+#ifndef __cpp_impl_three_way_comparison
+  GTEST_SKIP() << "C++20 three-way <=> comparison not supported";
+#else
+  EXPECT_EQ(absl::string_view("a") <=> absl::Cord("a"),
+            std::strong_ordering::equal);
+  EXPECT_EQ(absl::Cord("a") <=> absl::string_view("b"),
+            std::strong_ordering::less);
+  EXPECT_EQ(absl::string_view("b") <=> absl::Cord("a"),
+            std::strong_ordering::greater);
+#endif
+}
+
 #if defined(GTEST_HAS_DEATH_TEST) && defined(ABSL_INTERNAL_CORD_HAVE_SANITIZER)
 
 // Returns an expected poison / uninitialized death message expression.