Output to the test warning file if no tests are linked.

Bazel sets the environment variable TEST_WARNINGS_OUTPUT_FILE
https://bazel.build/reference/test-encyclopedia#initial-conditions

If no tests are linked and the new flag --gtest_fail_if_no_test_linked
is not true (which is the current default), we can still warn the user
as this may be a programming error without failing the test (which would
break existing users).

PiperOrigin-RevId: 731402363
Change-Id: Ia481689efd4bd18889feaaa38bc56049a3f651cd

googletest/src/gtest.cc

@@ -192,12 +192,17 @@ static const char kDefaultOutputFormat[] = "xml";
 // The default output file.
 static const char kDefaultOutputFile[] = "test_detail";
 
+// These environment variables are set by Bazel.
+// https://bazel.build/reference/test-encyclopedia#initial-conditions
+//
 // The environment variable name for the test shard index.
 static const char kTestShardIndex[] = "GTEST_SHARD_INDEX";
 // The environment variable name for the total number of test shards.
 static const char kTestTotalShards[] = "GTEST_TOTAL_SHARDS";
 // The environment variable name for the test shard status file.
 static const char kTestShardStatusFile[] = "GTEST_SHARD_STATUS_FILE";
+// The environment variable name for the test output warnings file.
+static const char kTestWarningsOutputFile[] = "TEST_WARNINGS_OUTPUT_FILE";
 
 namespace internal {
 
@@ -5875,6 +5880,23 @@ TestSuite* UnitTestImpl::GetTestSuite(
 static void SetUpEnvironment(Environment* env) { env->SetUp(); }
 static void TearDownEnvironment(Environment* env) { env->TearDown(); }
 
+// If the environment variable TEST_WARNINGS_OUTPUT_FILE was provided, appends
+// `str` to the file, creating the file if necessary.
+#if GTEST_HAS_FILE_SYSTEM
+static void AppendToTestWarningsOutputFile(const std::string& str) {
+  const char* const filename = posix::GetEnv(kTestWarningsOutputFile);
+  if (filename == nullptr) {
+    return;
+  }
+  auto* const file = posix::FOpen(filename, "a");
+  if (file == nullptr) {
+    return;
+  }
+  GTEST_CHECK_(fwrite(str.data(), 1, str.size(), file) == str.size());
+  GTEST_CHECK_(posix::FClose(file) == 0);
+}
+#endif  // GTEST_HAS_FILE_SYSTEM
+
 // Runs all tests in this UnitTest object, prints the result, and
 // returns true if all tests are successful.  If any exception is
 // thrown during a test, the test is considered to be failed, but the
@@ -5896,13 +5918,27 @@ bool UnitTestImpl::RunAllTests() {
   // user didn't call InitGoogleTest.
   PostFlagParsingInit();
 
-  if (GTEST_FLAG_GET(fail_if_no_test_linked) && total_test_count() == 0) {
+  // Handle the case where the program has no tests linked.
+  // Sometimes this is a programmer mistake, but sometimes it is intended.
+  if (total_test_count() == 0) {
+    constexpr char kNoTestLinkedMessage[] =
+        "This test program does NOT link in any test case.";
+    constexpr char kNoTestLinkedFatal[] =
+        "This is INVALID. Please make sure to link in at least one test case.";
+    constexpr char kNoTestLinkedWarning[] =
+        "Please make sure this is intended.";
+    const bool fail_if_no_test_linked = GTEST_FLAG_GET(fail_if_no_test_linked);
     ColoredPrintf(
-        GTestColor::kRed,
+        GTestColor::kRed, "%s %s\n", kNoTestLinkedMessage,
-        "This test program does NOT link in any test case. This is INVALID. "
+        fail_if_no_test_linked ? kNoTestLinkedFatal : kNoTestLinkedWarning);
-        "Please make sure to link in at least one test case.\n");
+    if (fail_if_no_test_linked) {
       return false;
     }
+#if GTEST_HAS_FILE_SYSTEM
+    AppendToTestWarningsOutputFile(std::string(kNoTestLinkedMessage) + ' ' +
+                                   kNoTestLinkedWarning + '\n');
+#endif  // GTEST_HAS_FILE_SYSTEM
+  }
 
 #if GTEST_HAS_FILE_SYSTEM
   // Even if sharding is not on, test runners may want to use the

googletest/test/googletest-fail-if-no-test-linked-test.py

@@ -31,21 +31,26 @@
 
 """Tests for Google Test's --gtest_fail_if_no_test_linked flag."""
 
+import os
 from googletest.test import gtest_test_utils
 
 # The command line flag for enabling the fail-if-no-test-linked behavior.
 FAIL_IF_NO_TEST_LINKED_FLAG = "gtest_fail_if_no_test_linked"
 
+# The environment variable for the test output warnings file.
+TEST_WARNINGS_OUTPUT_FILE = "TEST_WARNINGS_OUTPUT_FILE"
+
 
 class GTestFailIfNoTestLinkedTest(gtest_test_utils.TestCase):
   """Tests the --gtest_fail_if_no_test_linked flag."""
 
-  def Run(self, program_name, flag=None):
+  def Run(self, program_name, flag=None, env=None):
     """Run the given program with the given flag.
 
     Args:
       program_name: Name of the program to run.
       flag: The command line flag to pass to the program, or None.
+      env: Dictionary with environment to pass to the subprocess.
 
     Returns:
       True if the program exits with code 0, false otherwise.
@@ -55,59 +60,109 @@ class GTestFailIfNoTestLinkedTest(gtest_test_utils.TestCase):
     args = [exe_path]
     if flag is not None:
       args += [flag]
-    process = gtest_test_utils.Subprocess(args, capture_stderr=False)
+    process = gtest_test_utils.Subprocess(args, capture_stderr=False, env=env)
     return process.exited and process.exit_code == 0
 
   def testSucceedsIfNoTestLinkedAndFlagNotSpecified(self):
     """Tests the behavior of no test linked and flag not specified."""
-
     self.assertTrue(
         self.Run("googletest-fail-if-no-test-linked-test-without-test_")
     )
 
+  def testSucceedsIfNoTestLinkedAndFlagNotSpecifiedWithWarningFile(self):
+    """Tests that no test linked results in warning file output."""
+
+    warning_file = os.path.join(gtest_test_utils.GetTempDir(), "NO_TEST_LINKED")
+    self.assertTrue(
+        self.Run(
+            "googletest-fail-if-no-test-linked-test-without-test_",
+            env={TEST_WARNINGS_OUTPUT_FILE: warning_file},
+        )
+    )
+    warning_file_contents = open(warning_file, "r").read()
+    self.assertEqual(
+        warning_file_contents,
+        "This test program does NOT link in any test case. Please make sure"
+        " this is intended.\n",
+    )
+
   def testFailsIfNoTestLinkedAndFlagSpecified(self):
     """Tests the behavior of no test linked and flag specified."""
 
+    warning_file = os.path.join(
+        gtest_test_utils.GetTempDir(), "SHOULD_NOT_EXIST"
+    )
     self.assertFalse(
         self.Run(
             "googletest-fail-if-no-test-linked-test-without-test_",
             f"--{FAIL_IF_NO_TEST_LINKED_FLAG}",
+            env={TEST_WARNINGS_OUTPUT_FILE: warning_file},
         )
     )
+    with self.assertRaises(FileNotFoundError):
+      open(warning_file, "r")
 
   def testSucceedsIfEnabledTestLinkedAndFlagNotSpecified(self):
     """Tests the behavior of enabled test linked and flag not specified."""
 
-    self.assertTrue(
+    warning_file = os.path.join(
-        self.Run("googletest-fail-if-no-test-linked-test-with-enabled-test_")
+        gtest_test_utils.GetTempDir(), "SHOULD_NOT_EXIST"
     )
+    self.assertTrue(
+        self.Run(
+            "googletest-fail-if-no-test-linked-test-with-enabled-test_",
+            env={TEST_WARNINGS_OUTPUT_FILE: warning_file},
+        )
+    )
+    with self.assertRaises(FileNotFoundError):
+      open(warning_file, "r")
 
   def testSucceedsIfEnabledTestLinkedAndFlagSpecified(self):
     """Tests the behavior of enabled test linked and flag specified."""
 
+    warning_file = os.path.join(
+        gtest_test_utils.GetTempDir(), "SHOULD_NOT_EXIST"
+    )
     self.assertTrue(
         self.Run(
             "googletest-fail-if-no-test-linked-test-with-enabled-test_",
             f"--{FAIL_IF_NO_TEST_LINKED_FLAG}",
+            env={TEST_WARNINGS_OUTPUT_FILE: warning_file},
         )
     )
+    with self.assertRaises(FileNotFoundError):
+      open(warning_file, "r")
 
   def testSucceedsIfDisabledTestLinkedAndFlagNotSpecified(self):
     """Tests the behavior of disabled test linked and flag not specified."""
 
-    self.assertTrue(
+    warning_file = os.path.join(
-        self.Run("googletest-fail-if-no-test-linked-test-with-disabled-test_")
+        gtest_test_utils.GetTempDir(), "SHOULD_NOT_EXIST"
     )
+    self.assertTrue(
+        self.Run(
+            "googletest-fail-if-no-test-linked-test-with-disabled-test_",
+            env={TEST_WARNINGS_OUTPUT_FILE: warning_file},
+        )
+    )
+    with self.assertRaises(FileNotFoundError):
+      open(warning_file, "r")
 
   def testSucceedsIfDisabledTestLinkedAndFlagSpecified(self):
     """Tests the behavior of disabled test linked and flag specified."""
 
+    warning_file = os.path.join(
+        gtest_test_utils.GetTempDir(), "SHOULD_NOT_EXIST"
+    )
     self.assertTrue(
         self.Run(
             "googletest-fail-if-no-test-linked-test-with-disabled-test_",
             f"--{FAIL_IF_NO_TEST_LINKED_FLAG}",
+            env={TEST_WARNINGS_OUTPUT_FILE: warning_file},
         )
     )
+    with self.assertRaises(FileNotFoundError):
+      open(warning_file, "r")
 
 
 if __name__ == "__main__":