[unittest] teach gTest to print entries of DenseMap as pairs

When an assertion like the following fails:
   EXPECT_THAT(map, ElementsAre(Pair("p", "nullable"))));
Error message before:
   Actual: { 40-byte object <E8-A5 9C-7F 25-37 00-00 58-7E 51-51 D0-7F 00-00 00-00 00-00 00-00 00-00 01-00 00-00 00-00 00-00 00-DA C7-7F 25-37 00-00> }
After:
   Actual: { ("p", "nonnull") }

It is not ideal that we need to refer directly to DenseMapPair inside the
internal namespace, but I believe the practical maintenance risk is low.
This change is covered by DenseMap's unittests, as we've covered SmallString etc
in the past.

Differential Revision: https://reviews.llvm.org/D153930

2 files changed, 21 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/DenseMapTest.cpp b/llvm/unittests/ADT/DenseMapTest.cpp
index 94764a8..cc32445 100644
--- a/llvm/unittests/ADT/DenseMapTest.cpp
+++ b/llvm/unittests/ADT/DenseMapTest.cpp
@@ -9,6 +9,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/DenseMapInfoVariant.h"
+#include "llvm/ADT/StringRef.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <map>
@@ -756,4 +757,12 @@ TEST(DenseMapCustomTest, VariantSupport) {
   // operator==.
   EXPECT_FALSE(DenseMapInfo<variant>::isEqual(Keys[2], Keys[2]));
 }
+
+// Test that gTest prints map entries as pairs instead of opaque objects.
+// See third-party/unittest/googletest/internal/custom/gtest-printers.h
+TEST(DenseMapCustomTest, PairPrinting) {
+  DenseMap<int, StringRef> Map = {{1, "one"}, {2, "two"}};
+  EXPECT_EQ(R"({ (1, "one"), (2, "two") })", ::testing::PrintToString(Map));
+}
+
 } // namespace
diff --git a/third-party/unittest/googletest/include/gtest/internal/custom/gtest-printers.h b/third-party/unittest/googletest/include/gtest/internal/custom/gtest-printers.h
index b732092..f279221 100644
--- a/third-party/unittest/googletest/include/gtest/internal/custom/gtest-printers.h
+++ b/third-party/unittest/googletest/include/gtest/internal/custom/gtest-printers.h
@@ -40,6 +40,7 @@
 #define GTEST_INCLUDE_GTEST_INTERNAL_CUSTOM_GTEST_PRINTERS_H_
 
 #if !GTEST_NO_LLVM_SUPPORT
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
 #include <ostream>
@@ -63,6 +64,17 @@ inline void PrintTo(const SmallString<N> &S, std::ostream *OS) {
 inline void PrintTo(const SmallVectorImpl<char> &S, std::ostream *OS) {
   *OS << ::testing::PrintToString(std::string(S.data(), S.size()));
 }
+
+// DenseMap's entries inherit from std::pair, and should act like pairs.
+// However gTest's provided `PrintTo(pair<K,V>)` template won't deduce K and V
+// because of the needed derived-to-base conversion.
+namespace detail {
+template <typename K, typename V>
+inline void PrintTo(const DenseMapPair<K, V> &Pair, std::ostream *OS) {
+  *OS << ::testing::PrintToString(static_cast<const std::pair<K, V> &>(Pair));
+}
+} // namespace detail
+
 } // namespace llvm
 #endif // !GTEST_NO_LLVM_SUPPORT