Properly convert proto to text

`ProtobufPrinter` used to `absl::StrCat` protos into code snippets, which is intentionally unparseable.

This CL replaces that with a proper proto -> text conversion.

PiperOrigin-RevId: 625803909

fuzztest/BUILD

diff --git a/fuzztest/BUILD b/fuzztest/BUILD
index 38990c3..4ffc4f3 100644
--- a/fuzztest/BUILD
+++ b/fuzztest/BUILD
@@ -721,6 +721,7 @@
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/strings:str_format",
         "@com_google_absl//absl/time",
+        "@com_google_protobuf//:protobuf",
     ],
 )
 
@@ -738,5 +739,6 @@
         "@com_google_absl//absl/strings:str_format",
         "@com_google_absl//absl/time",
         "@com_google_googletest//:gtest_main",
+        "@com_google_protobuf//:protobuf",
     ],
 )

fuzztest/internal/type_support.h

diff --git a/fuzztest/internal/type_support.h b/fuzztest/internal/type_support.h
index d068992..88804af 100644
--- a/fuzztest/internal/type_support.h
+++ b/fuzztest/internal/type_support.h
@@ -31,6 +31,7 @@
 #include "absl/strings/escaping.h"
 #include "absl/strings/has_absl_stringify.h"
 #include "absl/strings/match.h"
+#include "absl/strings/str_cat.h"
 #include "absl/strings/str_format.h"
 #include "absl/strings/string_view.h"
 #include "absl/strings/strip.h"
@@ -38,6 +39,7 @@
 #include "./fuzztest/internal/domains/absl_helpers.h"
 #include "./fuzztest/internal/meta.h"
 #include "./fuzztest/internal/printer.h"
+#include "google/protobuf/text_format.h"
 
 namespace fuzztest::internal {
 
@@ -255,13 +257,18 @@
       return PrintUserValue(*val, out, mode);
     } else {
       static constexpr absl::string_view kProtoParser = "ParseTestProto";
+      std::string textproto;
+      if (!google::protobuf::TextFormat::PrintToString(val, &textproto)) {
+        // Fall-back to debug printing, which is on purpose not parseable but at
+        // least gives some idea about the contents of the proto.
+        textproto = absl::StrCat(val);
+      }
       switch (mode) {
         case domain_implementor::PrintMode::kHumanReadable:
-          absl::Format(out, "(%s)", absl::StrCat(val));
+          absl::Format(out, "(%s)", textproto);
           break;
         case domain_implementor::PrintMode::kSourceCode:
-          absl::Format(out, "%s(R\"pb(%s)pb\")", kProtoParser,
-                       absl::StrCat(val));
+          absl::Format(out, "%s(R\"pb(%s)pb\")", kProtoParser, textproto);
           break;
       }
     }

fuzztest/internal/type_support_test.cc

diff --git a/fuzztest/internal/type_support_test.cc b/fuzztest/internal/type_support_test.cc
index 354c6a3..286d1b6 100644
--- a/fuzztest/internal/type_support_test.cc
+++ b/fuzztest/internal/type_support_test.cc
@@ -45,6 +45,7 @@
 #include "./fuzztest/internal/meta.h"
 #include "./fuzztest/internal/printer.h"
 #include "./fuzztest/internal/test_protobuf.pb.h"
+#include "google/protobuf/text_format.h"
 
 namespace fuzztest::internal {
 namespace {
@@ -228,11 +229,13 @@
   internal::TestProtobuf proto;
   proto.set_b(true);
   proto.add_rep_subproto()->set_subproto_i32(17);
+  std::string proto_text;
+  ASSERT_TRUE(google::protobuf::TextFormat::PrintToString(proto, &proto_text));
   EXPECT_THAT(TestPrintValue(proto),
-              ElementsAre(absl::StrCat("(", proto, ")"),
+              ElementsAre(absl::StrCat("(", proto_text, ")"),
                           MatchesRegex(absl::StrCat(
-                              R"re(.*ParseTe[sx]tProto.*\(R"pb\()re", proto,
-                              R"re(\)pb"\))re"))));
+                              R"re(.*ParseTe[sx]tProto.*\(R"pb\()re",
+                              proto_text, R"re(\)pb"\))re"))));
 }
 
 TEST(ProtobufEnumTest, Printer) {