Use the output directory for relative corpus path when fuzzing.

PiperOrigin-RevId: 835240175

Author: hadi88

fuzztest/init_fuzztest.cc

@@ -348,10 +348,20 @@ internal::Configuration CreateConfigurationsFromFlags(
       << "If specified, --" << FUZZTEST_FLAG(jobs).Name()
       << " must be positive.";
   std::string corpus_database = absl::GetFlag(FUZZTEST_FLAG(corpus_database));
-  if (!corpus_database.empty() && corpus_database[0] != '/' &&
-      std::getenv("TEST_SRCDIR")) {
-    corpus_database =
-        absl::StrCat(std::getenv("TEST_SRCDIR"), "/", corpus_database);
+  if (!corpus_database.empty() && corpus_database[0] != '/') {
+    // When fuzzing, pick the undeclared output directory for a relative corpus
+    // database path, because the output directory is writable. Otherwise, pick
+    // the test srcdir (read-only) as the current directory when dealing with a
+    // relative corpus database path.
+    if (fuzzing_time_limit) {  // Need a writable directory.
+      if (std::getenv("TEST_UNDECLARED_OUTPUTS_DIR")) {
+        corpus_database = absl::StrCat(
+            std::getenv("TEST_UNDECLARED_OUTPUTS_DIR"), "/", corpus_database);
+      }
+    } else if (std::getenv("TEST_SRCDIR")) {  // Need a read-only directory.
+      corpus_database =
+          absl::StrCat(std::getenv("TEST_SRCDIR"), "/", corpus_database);
+    }
   }
   return internal::Configuration{
       corpus_database,