Provide the default lcov_merger to all Starlark tests

Since 5b216b2, all Starlark-defined test rules either need to set the
`_lcov_merger` attribute or fail if run with `bazel coverage`. This is
fixed by attaching the default lcov merger as a late-bound default to
all Starlark rules via a new attribute and falling back to that
attribute in the TestActionBuilder.

This commit ensures backwards compatibility is maintained with existing
Starlark test rules that set the `_lcov_merger` attribute. This is also
verified in the included integration test.

Fixes #13978.

src/main/java/com/google/devtools/build/lib/analysis/starlark/StarlarkRuleClassFunctions.java

@@ -248,6 +248,10 @@ public static RuleClass getTestBaseRule(RuleDefinitionEnvironment env) {
                         BaseRuleClasses.coverageSupportAttribute(
                             labelCache.get(
                                 toolsRepository + BaseRuleClasses.DEFAULT_COVERAGE_SUPPORT_VALUE))))
+            .add(
+                attr(":default_lcov_merger", LABEL)
+                    .cfg(HostTransition.createFactory())
+                    .value(BaseRuleClasses.getCoverageOutputGeneratorLabel()))
             // Used in the one-per-build coverage report generation action.
             .add(
                 attr(":coverage_report_generator", LABEL)

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

@@ -269,6 +269,8 @@ private TestParams createTestAction(int shards)
         lcovMergerAttr = ":lcov_merger";
       } else if (ruleContext.isAttrDefined("$lcov_merger", LABEL)) {
         lcovMergerAttr = "$lcov_merger";
+      } else if (ruleContext.isAttrDefined(":default_lcov_merger", LABEL)) {
+        lcovMergerAttr = ":default_lcov_merger";
       }
       if (lcovMergerAttr != null) {
         TransitiveInfoCollection lcovMerger = ruleContext.getPrerequisite(lcovMergerAttr);

src/test/shell/bazel/BUILD

@@ -554,6 +554,15 @@ sh_test(
     ],
 )
 
+sh_test(
+    name = "bazel_coverage_starlark_test",
+    srcs = ["bazel_coverage_starlark_test.sh"],
+    data = [":test-deps"],
+    tags = [
+        "no_windows",
+    ],
+)
+
 sh_test(
     name = "bazel_thinlto_test",
     srcs = ["bazel_thinlto_test.sh"],

src/test/shell/bazel/bazel_coverage_starlark_test.sh

@@ -0,0 +1,137 @@
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eu
+
+# Load the test setup defined in the parent directory
+CURRENT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "${CURRENT_DIR}/../integration_test_setup.sh" \
+  || { echo "integration_test_setup.sh not found!" >&2; exit 1; }
+
+# Returns the path of the code coverage report that was generated by Bazel by
+# looking at the current $TEST_log. The method fails if TEST_log does not
+# contain any coverage report for a passed test.
+function get_coverage_file_path_from_test_log() {
+  local ending_part="$(sed -n -e '/PASSED/,$p' "$TEST_log")"
+
+  local coverage_file_path=$(grep -Eo "/[/a-zA-Z0-9\.\_\-]+\.dat$" <<< "$ending_part")
+  [[ -e "$coverage_file_path" ]] || fail "Coverage output file does not exist!"
+  echo "$coverage_file_path"
+}
+
+function test_coverage_custom_rule_without_lcov_merger() {
+  local workspace="${FUNCNAME[0]}"
+  mkdir -p "${workspace}"
+
+  touch "${workspace}/WORKSPACE"
+  cat >> "${workspace}/BUILD" << EOF
+load(":rules.bzl", "custom_test")
+
+custom_test(
+    name = "custom_test",
+)
+
+EOF
+  cat >> "${workspace}/rules.bzl" << EOF
+def _custom_test_impl(ctx):
+    executable = ctx.actions.declare_file(ctx.attr.name)
+    ctx.actions.write(executable, "", is_executable = True)
+    return [
+        DefaultInfo(
+            executable = executable,
+        ),
+    ]
+
+custom_test = rule(
+    implementation = _custom_test_impl,
+    test = True,
+)
+EOF
+
+  cd "${workspace}"
+  bazel test //:custom_test  &>"$TEST_log" \
+      || fail "Test failed without coverage but should have succeeded"
+
+  bazel coverage //:custom_test  &>"$TEST_log" \
+      || fail "Test failed with coverage but should have succeeded"
+}
+
+function test_coverage_custom_rule_with_custom_lcov_merger() {
+  local workspace="${FUNCNAME[0]}"
+  mkdir -p "${workspace}"
+
+  touch "${workspace}/WORKSPACE"
+  cat >> "${workspace}/BUILD" << EOF
+load(":rules.bzl", "custom_test")
+
+java_binary(
+    name = "merger",
+    srcs = ["Merger.java"],
+    main_class = "Merger",
+)
+
+custom_test(
+    name = "custom_test",
+)
+
+EOF
+  cat >> "${workspace}/rules.bzl" << EOF
+def _custom_test_impl(ctx):
+    executable = ctx.actions.declare_file(ctx.attr.name)
+    ctx.actions.write(executable, "", is_executable = True)
+    return [
+        DefaultInfo(
+            executable = executable,
+        ),
+    ]
+
+custom_test = rule(
+    implementation = _custom_test_impl,
+    test = True,
+    attrs = {
+        "_lcov_merger": attr.label(
+            default = ":merger",
+            executable = True,
+            cfg = "host",
+        ),
+    }
+)
+EOF
+  cat >> "${workspace}/Merger.java" << EOF
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Paths;
+
+public class Merger {
+  public static void main(String[] args) throws IOException {
+    for (String arg : args) {
+      if (arg.startsWith("--output_file=")) {
+        String coverageFile = arg.substring("--output_file=".length());
+        Files.write(Paths.get(coverageFile), "custom_merger_ran".getBytes());
+      }
+    }
+  }
+}
+EOF
+
+  cd "${workspace}"
+  bazel test //:custom_test  &>"$TEST_log" \
+      || fail "Test failed without coverage but should have succeeded"
+
+  bazel coverage //:custom_test  &>"$TEST_log" \
+      || fail "Test failed with coverage but should have succeeded"
+  local coverage_file_path="$( get_coverage_file_path_from_test_log )"
+  grep -F "custom_merger_ran" "$coverage_file_path" \
+        || fail "Failed to find message from custom merger"
+}
+
+run_suite "test coverage_starlark_test"