Actually check TEST_SHARD_STATUS_FILE has been touched

Adds the missing check that a test runner running a sharded test
actually supports sharding. Previously, if it didn't, each shard would
silently run all tests.

RELNOTES: If sharding is requested for a test but the test runner does
not advertise support for test sharding by touching the
`TEST_SHARD_STATUS_FILE`, the tests will fail instead of silently
running all tests in each shard.

src/test/py/bazel/bazel_windows_test.py

@@ -449,6 +449,31 @@ def testZipUndeclaredTestOutputs(self):
     self.assertTrue(os.path.exists(output_file))
     self.assertFalse(os.path.exists(output_zip))
 
+  def testTestShardStatusFile(self):
+    self.CreateWorkspaceWithDefaultRepos('WORKSPACE')
+    self.ScratchFile(
+        'BUILD',
+        [
+          'sh_test(',
+          '  name = "foo_test",',
+          '  srcs = ["foo.sh"],',
+          '  shard_count = 2,',
+          ')',
+        ],
+    )
+    self.ScratchFile('foo.sh')
+
+    exit_code, _, stderr = self.RunBazel(['test', '//:foo_test'])
+    # Check for "tests failed" exit code
+    self.AssertExitCode(exit_code, 3, stderr)
+    self.assertIn("Sharding requested, but the test runner did not advertise "
+                  "support for it by touching TEST_SHARD_STATUS_FILE.", stderr)
+
+    self.ScratchFile('foo.sh', ['touch "$TEST_SHARD_STATUS_FILE"'])
+
+    exit_code, _, stderr = self.RunBazel(['test', '//:foo_test'])
+    self.AssertExitCode(exit_code, 0, stderr)
+
 
 if __name__ == '__main__':
   unittest.main()

src/test/shell/bazel/bazel_test_test.sh

@@ -997,4 +997,24 @@ EOF
   expect_log "<testcase name=\"x\""
 }
 
+function test_shard_status_file_checked() {
+  cat <<'EOF' > BUILD
+sh_test(
+    name = 'x',
+    srcs = ['x.sh'],
+    shard_count = 2,
+)
+EOF
+  touch x.sh
+  chmod +x x.sh
+
+  bazel test //:x --test_output=errors &> $TEST_log \
+      && fail "expected failure"
+  expect_log "Sharding requested, but the test runner did not advertise support for it by touching TEST_SHARD_STATUS_FILE."
+
+  echo 'touch "$TEST_SHARD_STATUS_FILE"' > x.sh
+  bazel test //:x --test_output=errors &> $TEST_log \
+      || fail "expected success"
+}
+
 run_suite "bazel test tests"

tools/test/test-setup.sh

@@ -75,6 +75,9 @@ fi
 if [[ -n "$TEST_SHARD_STATUS_FILE" ]]; then
   is_absolute "$TEST_SHARD_STATUS_FILE" || TEST_SHARD_STATUS_FILE="$PWD/$TEST_SHARD_STATUS_FILE"
   mkdir -p "$(dirname "$TEST_SHARD_STATUS_FILE")"
+  # Get the modification time in nano second granularity or record that it was missing.
+  TEST_SHARD_STATUS_FILE_MTIME_AT_START=$(stat -c '%.9Y' "$TEST_SHARD_STATUS_FILE" 2> /dev/null ||
+    echo "missing")
 fi
 
 is_absolute "$RUNFILES_DIR" || RUNFILES_DIR="$PWD/$RUNFILES_DIR"
@@ -368,6 +371,16 @@ kill_group SIGKILL $childPid
 kill_group SIGKILL $cleanupPid &> /dev/null
 wait $cleanupPid
 
+# Sharding was requested, verify that the test runner actually supported it.
+if [[ -n "$TEST_SHARD_STATUS_FILE" ]]; then
+  TEST_SHARD_STATUS_FILE_MTIME_AT_END=$(stat -c '%.9Y' "$TEST_SHARD_STATUS_FILE" 2> /dev/null ||
+    echo "missing")
+  if [[ "$TEST_SHARD_STATUS_FILE_MTIME_AT_START" = "$TEST_SHARD_STATUS_FILE_MTIME_AT_END" ]]; then
+    echo >&2 "Sharding requested, but the test runner did not advertise support for it by touching TEST_SHARD_STATUS_FILE. Either remove the 'shard_count' attribute or use a test runner that supports sharding."
+    exit 1
+  fi
+fi
+
 for signal in $signals; do
   trap - ${signal}
 done

tools/test/windows/tw.cc

@@ -605,6 +605,42 @@ bool ExportShardStatusFile(const Path& cwd) {
          CreateDirectories(status_file.Dirname());
 }
 
+bool GetLenientShardStatusFileModificationTime(uint64_t* mtime) {
+  Path status_file;
+  if (!GetPathEnv(L"TEST_SHARD_STATUS_FILE", &status_file) ||
+      status_file.Get().empty()) {
+    return false;
+  }
+
+  bazel::windows::AutoHandle handle(CreateFileW(
+      AddUncPrefixMaybe(status_file).c_str(), GENERIC_READ,
+      FILE_SHARE_READ | FILE_SHARE_DELETE, nullptr, OPEN_EXISTING,
+      FILE_ATTRIBUTE_NORMAL, nullptr));
+  if (!handle.IsValid()) {
+    DWORD err = GetLastError();
+    if (err != ERROR_FILE_NOT_FOUND) {
+      LogErrorWithArgAndValue(
+          __LINE__, "Failed to open shard status file", status_file.Get(), err);
+    }
+    *mtime = 0;
+    return true;
+  }
+
+  FILETIME lastWriteTime;
+  if (!GetFileTime(handle, nullptr, nullptr, &lastWriteTime)) {
+    DWORD err = GetLastError();
+    LogErrorWithArgAndValue(
+        __LINE__, "Failed to get file time of shard status file",
+        status_file.Get(), err);
+    *mtime = 0;
+    return true;
+  }
+
+  *mtime = ((uint64_t) lastWriteTime.dwHighDateTime << 32) |
+      lastWriteTime.dwLowDateTime;
+  return true;
+}
+
 bool ExportGtestVariables(const Path& test_tmpdir) {
   // # Tell googletest about Bazel sharding.
   std::wstring total_shards_str;
@@ -1925,6 +1961,7 @@ int TestWrapperMain(int argc, wchar_t** argv) {
   Path test_path, exec_root, srcdir, tmpdir, test_outerr, xml_log;
   UndeclaredOutputs undecl;
   std::wstring args;
+  uint64_t shard_status_file_mtime_start, shard_status_file_mtime_end;
   if (!AddCurrentDirectoryToPATH() ||
       !ParseArgs(argc, argv, &argv0, &test_path_arg, &args) ||
       !PrintTestLogStartMarker() || !GetCwd(&exec_root) || !ExportUserName() ||
@@ -1939,8 +1976,17 @@ int TestWrapperMain(int argc, wchar_t** argv) {
     return 1;
   }
 
+  GetLenientShardStatusFileModificationTime(&shard_status_file_mtime_start);
   Duration test_duration;
   int result = RunSubprocess(test_path, args, test_outerr, &test_duration);
+  if (GetLenientShardStatusFileModificationTime(&shard_status_file_mtime_end) &&
+      shard_status_file_mtime_start == shard_status_file_mtime_end) {
+    LogError(__LINE__, "Sharding requested, but the test runner did not"
+        " advertise support for it by touching TEST_SHARD_STATUS_FILE. Either"
+        " remove the 'shard_count' attribute or use a test runner that supports"
+        " sharding.");
+    return 1;
+  }
   if (!CreateXmlLog(xml_log, test_outerr, test_duration, result,
                     DeleteAfterwards::kEnabled, MainType::kTestWrapperMain) ||
       !ArchiveUndeclaredOutputs(undecl) ||