Actually check TEST_SHARD_STATUS_FILE has been touched

site/en/reference/test-encyclopedia.md

@@ -225,8 +225,9 @@ shard index, beginning at 0. Runners use this information to select which tests
 to run - for example, using a round-robin strategy. Not all test runners support
 sharding. If a runner supports sharding, it must create or update the last
 modified date of the file specified by
-[`TEST_SHARD_STATUS_FILE`](#initial-conditions). Otherwise, Bazel assumes it
-does not support sharding and will not launch additional runners.
+[`TEST_SHARD_STATUS_FILE`](#initial-conditions). Otherwise, if
+[`--incompatible_check_sharding_support`](/reference/command-line-reference#flag--incompatible_check_sharding_support)
+is enabled, Bazel will fail the test if it is sharded.
 
 ## Initial conditions {:#initial-conditions}
 

src/main/java/com/google/devtools/build/lib/analysis/test/TestConfiguration.java

@@ -291,6 +291,19 @@ public static class TestOptions extends FragmentOptions {
                 + "the test exec group.")
     public boolean useTargetPlatformForTests;
 
+    @Option(
+        name = "incompatible_check_sharding_support",
+        defaultValue = "false",
+        documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
+        metadataTags = {OptionMetadataTag.INCOMPATIBLE_CHANGE},
+        effectTags = {OptionEffectTag.UNKNOWN},
+        help =
+            "If true, Bazel will fail a sharded test if the test runner does not indicate that it "
+                + "supports sharding by touching the file at the path in TEST_SHARD_STATUS_FILE. "
+                + "If false, a test runner that does not support sharding will lead to all tests "
+                + "running in each shard.")
+    public boolean checkShardingSupport;
+
     @Override
     public FragmentOptions getExec() {
       // Options here are either:
@@ -395,6 +408,10 @@ public boolean useTargetPlatformForTests() {
     return options.useTargetPlatformForTests;
   }
 
+  public boolean checkShardingSupport() {
+    return options.checkShardingSupport;
+  }
+
   /**
    * Option converter that han handle two styles of value for "--runs_per_test":
    *

src/main/java/com/google/devtools/build/lib/analysis/test/TestRunnerAction.java

@@ -332,6 +332,10 @@ public boolean showsOutputUnconditionally() {
     return true;
   }
 
+  public boolean checkShardingSupport() {
+    return testConfiguration.checkShardingSupport();
+  }
+
   public List<ActionInput> getSpawnOutputs() {
     final List<ActionInput> outputs = new ArrayList<>();
     outputs.add(ActionInputHelper.fromPath(getXmlOutputPath()));

src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java

@@ -684,6 +684,22 @@ private TestAttemptResult runTestAttempt(
     }
     long endTimeMillis = actionExecutionContext.getClock().currentTimeMillis();
 
+    if (testAction.isSharded()) {
+      if (testAction.checkShardingSupport() && !actionExecutionContext.getPathResolver()
+          .convertPath(resolvedPaths.getTestShard()).exists()) {
+        TestExecException e =
+            createTestExecException(
+                TestAction.Code.LOCAL_TEST_PREREQ_UNMET,
+                "Sharding requested, but the test runner did not advertise support for it by "
+                    + "touching TEST_SHARD_STATUS_FILE. Either remove the 'shard_count' attribute, "
+                    + "use a test runner that supports sharding or temporarily disable this check "
+                    + "via --noincompatible_check_sharding_support.");
+        closeSuppressed(e, streamed);
+        closeSuppressed(e, fileOutErr);
+        throw e;
+      }
+    }
+
     // SpawnActionContext guarantees the first entry to correspond to the spawn passed in (there
     // may be additional entries due to tree artifact handling).
     SpawnResult primaryResult = spawnResults.get(0);

src/test/py/bazel/bazel_windows_test.py

@@ -449,6 +449,34 @@ 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, stdout, stderr = self.RunBazel(
+        ['test', '--incompatible_check_sharding_support', '//:foo_test'])
+    # Check for "tests failed" exit code
+    self.AssertExitCode(exit_code, 3, stderr, stdout)
+    self.assertTrue(any(
+        "Sharding requested, but the test runner did not advertise support for"
+        " it by touching TEST_SHARD_STATUS_FILE." in line for line in stderr))
+
+    self.ScratchFile('foo.sh', ['touch "$TEST_SHARD_STATUS_FILE"'])
+
+    exit_code, stdout, stderr = self.RunBazel(
+        ['test', '--incompatible_check_sharding_support', '//:foo_test'])
+    self.AssertExitCode(exit_code, 0, stderr, stdout)
+
 
 if __name__ == '__main__':
   unittest.main()

src/test/shell/bazel/bazel_test_test.sh

@@ -997,4 +997,26 @@ 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 \
+      --incompatible_check_sharding_support \
+      //:x  &> $TEST_log && fail "expected failure"
+  expect_log "Sharding requested, but the test runner did not advertise support for it by touching TEST_SHARD_STATUS_FILE."
+
+  echo 'touch "$TEST_SHARD_STATUS_FILE"' > x.sh
+  bazel test \
+      --incompatible_check_sharding_support \
+      //:x  &> $TEST_log || fail "expected success"
+}
+
 run_suite "bazel test tests"

src/test/shell/bazel/remote/remote_execution_test.sh

@@ -3012,4 +3012,30 @@ function test_external_cc_binary_tool_with_dynamic_deps_sibling_repository_layou
       @other_repo//pkg:rule >& $TEST_log || fail "Build should succeed"
 }
 
+function test_shard_status_file_checked_remote_download_minimal() {
+  cat <<'EOF' > BUILD
+sh_test(
+    name = 'x',
+    srcs = ['x.sh'],
+    shard_count = 2,
+)
+EOF
+  touch x.sh
+  chmod +x x.sh
+
+  bazel test \
+      --remote_executor=grpc://localhost:${worker_port} \
+      --incompatible_check_sharding_support \
+      --remote_download_minimal \
+      //:x  &> $TEST_log && fail "expected failure"
+  expect_log "Sharding requested, but the test runner did not advertise support for it by touching TEST_SHARD_STATUS_FILE."
+
+  echo 'touch "$TEST_SHARD_STATUS_FILE"' > x.sh
+  bazel test \
+      --remote_executor=grpc://localhost:${worker_port} \
+      --incompatible_check_sharding_support \
+      --remote_download_minimal \
+      //:x  &> $TEST_log || fail "expected success"
+}
+
 run_suite "Remote execution and remote cache tests"