Print specific reproduction instruction if only one reproducer is exported.

PiperOrigin-RevId: 756386768

e2e_tests/functional_test.cc

diff --git a/e2e_tests/functional_test.cc b/e2e_tests/functional_test.cc
index 349b2e4..196daca 100644
--- a/e2e_tests/functional_test.cc
+++ b/e2e_tests/functional_test.cc
@@ -762,10 +762,9 @@
   EXPECT_THAT(args, Optional(FieldsAre(StartsWith("Fuzz")))) << std_err;
   EXPECT_THAT(std_err,
               AllOf(HasSubstr("Reproducer file was dumped at:"),
-                    HasSubstr(out_dir.path()),
-                    HasSubstr(Basename(replay_files[0].path)),
+                    HasSubstr(replay_files[0].path),
                     HasSubstr(absl::StrCat("--test_env=FUZZTEST_REPLAY=",
-                                           out_dir.path().string()))))
+                                           replay_files[0].path))))
       << std_err;
 }
 
@@ -785,14 +784,14 @@
   ASSERT_TRUE(parsed) << std_err;
   auto args = parsed->ToCorpus<std::tuple<std::string>>();
   EXPECT_THAT(args, Optional(FieldsAre(StartsWith("Fuzz")))) << std_err;
-  EXPECT_THAT(
-      std_err,
-      AllOf(HasSubstr("Reproducer file was dumped under "
-                      "TEST_UNDECLARED_OUTPUTS_DIR"
-                      ),
-            HasSubstr(out_dir.path()),
-            HasSubstr(Basename(replay_files[0].path)),
-            HasSubstr("--test_env=FUZZTEST_REPLAY=/tmp/fuzztest_repro/")))
+  EXPECT_THAT(std_err,
+              AllOf(HasSubstr("Reproducer file was dumped under "
+                              "TEST_UNDECLARED_OUTPUTS_DIR"
+                              ),
+                    HasSubstr(replay_files[0].path),
+                    HasSubstr(absl::StrCat(
+                        "--test_env=FUZZTEST_REPLAY=/tmp/fuzztest_repro/",
+                        Basename(replay_files[0].path)))))
       << std_err;
 }
 

fuzztest/internal/centipede_adaptor.cc

diff --git a/fuzztest/internal/centipede_adaptor.cc b/fuzztest/internal/centipede_adaptor.cc
index fb5bda9..c019d9f 100644
--- a/fuzztest/internal/centipede_adaptor.cc
+++ b/fuzztest/internal/centipede_adaptor.cc
@@ -751,6 +751,8 @@
                               "to report reproducers from Centipede");
   }
 
+  // Will be set when there is only one reproducer - nullopt otherwise.
+  std::optional<std::string> single_reproducer_path;
   for (const auto& exported_crash_file : *exported_crash_files) {
     if (!absl::EndsWith(exported_crash_file, ".data")) {
       continue;
@@ -790,16 +792,32 @@
     absl::FPrintF(GetStderr(),
                   "[.] Saved reproducer with ID %s and crash metadata %s\n",
                   Basename(reproducer_path), metadata);
+    if (!single_reproducer_path.has_value()) {
+      single_reproducer_path = reproducer_path;
+    } else {
+      // More than one reproducers are exported - use the placeholder for
+      // the instruction.
+      single_reproducer_path = std::nullopt;
+    }
   }
-  absl::FPrintF(GetStderr(),
-                "[.] Please follow the guide below for fetching and/or "
-                "replaying each reproducer files. You would need to replace "
-                "REPRODUCER_ID with the actual reproducer ID to be used.\n");
 
   ReportSink report_sink;
-  PrintReproducerIfRequested(
-      &report_sink, test, &configuration,
-      std::filesystem::path{output.dir_path}.append("REPRODUCER_ID").string());
+  if (single_reproducer_path.has_value()) {
+    PrintReproducerIfRequested(&report_sink, test, &configuration,
+                               *single_reproducer_path);
+  } else {
+    // TODO: b/385113025 - Test this branch when we no longer need to emulate
+    // the legacy exit-on-crash behavior.
+    absl::FPrintF(GetStderr(),
+                  "[.] Please follow the guide below for fetching and/or "
+                  "replaying each reproducer files. You would need to replace "
+                  "REPRODUCER_ID with the actual reproducer ID to be used.\n");
+    PrintReproducerIfRequested(&report_sink, test, &configuration,
+                               std::filesystem::path{output.dir_path}
+                                   .append("REPRODUCER_ID")
+                                   .string());
+  }
+
   return absl::OkStatus();
 }