Restore errno around allocation in test matchers

Allocation are not guaranteed to preserve errno, even in case of success.
Because the test matchers test against errno, preserve errno when allocating
new matchers.

PiperOrigin-RevId: 618437007

test/util/test_util.h

@@ -292,6 +292,20 @@ inline uint64_t ms_elapsed(const struct timespec& begin,
 
 namespace internal {
 
+// RAII class to restore errno. Used because malloc/new are not guaranteed to
+// preserve errno.
+class ErrnoRestorer {
+ public:
+  ErrnoRestorer() : saved_errno_(errno) {}
+  ~ErrnoRestorer() { errno = saved_errno_; }
+
+  ErrnoRestorer(const ErrnoRestorer&) = delete;
+  ErrnoRestorer& operator=(const ErrnoRestorer&) = delete;
+
+ private:
+  int saved_errno_;
+};
+
 template <typename Container>
 class ElementOfMatcher {
  public:
@@ -337,6 +351,8 @@ class SyscallSuccessMatcher {
 
   template <typename T>
   operator ::testing::Matcher<T>() const {
+    ErrnoRestorer errno_restorer;
+
     // E is one of three things:
     // - T, or a type losslessly and implicitly convertible to T.
     // - A monomorphic Matcher<T>.
@@ -393,6 +409,7 @@ class AnySuccessValueMatcher {
  public:
   template <typename T>
   operator ::testing::Matcher<T>() const {
+    ErrnoRestorer errno_restorer;
     return ::testing::MakeMatcher(new Impl<T>());
   }
 
@@ -473,6 +490,7 @@ class SpecificErrnoMatcher : public ::testing::MatcherInterface<int> {
 };
 
 inline ::testing::Matcher<int> SpecificErrno(int const expected) {
+  ErrnoRestorer errno_restorer;
   return ::testing::MakeMatcher(new SpecificErrnoMatcher(expected));
 }