Automatically add _lcov_merger and _collect_cc_coverage attributes

This makes it easier for test rules to support coverage as they no longer need to get the (undocumented) implicit attribute definitions right. In fact, the exec transition used in starlarkified native rules incorrectly used the default rather than the test exec group - the new default definitions of these attributes get this right.

Custom rules can continue to override the attributes as demonstrated by the existing `test_starlark_rule_with_custom_lcov_merger` test.

Author: fmeum

src/main/java/com/google/devtools/build/lib/analysis/BaseRuleClasses.java

@@ -151,7 +151,7 @@ public static LabelLateBoundDefault<CoverageConfiguration> coverageReportGenerat
         COVERAGE_REPORT_GENERATOR_CONFIGURATION_RESOLVER);
   }
 
-  public static LabelLateBoundDefault<CoverageConfiguration> getCoverageOutputGeneratorLabel() {
+  public static LabelLateBoundDefault<CoverageConfiguration> coverageOutputGeneratorAttribute() {
     return LabelLateBoundDefault.fromTargetConfiguration(
         CoverageConfiguration.class, null, COVERAGE_OUTPUT_GENERATOR_RESOLVER);
   }

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

@@ -294,6 +294,19 @@ public static RuleClass getTestBaseRule(RuleDefinitionEnvironment env) {
                     .cfg(ExecutionTransitionFactory.createFactory())
                     .singleArtifact()
                     .value(labelCache.get(toolsRepository + "//tools/test:collect_coverage")))
+            .add(
+                attr(":lcov_merger", LABEL)
+                    .cfg(
+                        ExecutionTransitionFactory.createFactory(
+                            DEFAULT_TEST_RUNNER_EXEC_GROUP_NAME))
+                    .value(BaseRuleClasses.coverageOutputGeneratorAttribute()))
+            .add(
+                attr("$collect_cc_coverage", LABEL)
+                    .cfg(
+                        ExecutionTransitionFactory.createFactory(
+                            DEFAULT_TEST_RUNNER_EXEC_GROUP_NAME))
+                    .singleArtifact()
+                    .value(labelCache.get(toolsRepository + "//tools/test:collect_cc_coverage")))
             // Input files for test actions collecting code coverage
             .add(
                 attr(":coverage_support", LABEL)

src/main/starlark/builtins_bzl/common/cc/semantics.bzl

@@ -71,18 +71,7 @@ def _get_test_malloc_attr():
     return {}
 
 def _get_coverage_attrs():
-    return {
-        "_lcov_merger": attr.label(
-            default = configuration_field(fragment = "coverage", name = "output_generator"),
-            executable = True,
-            cfg = "exec",
-        ),
-        "_collect_cc_coverage": attr.label(
-            default = "@bazel_tools//tools/test:collect_cc_coverage",
-            executable = True,
-            cfg = "exec",
-        ),
-    }
+    return {}
 
 def _get_coverage_env(ctx):
     return ctx.runfiles(), {}

src/test/shell/bazel/bazel_coverage_starlark_test.sh

@@ -252,10 +252,6 @@ _COMMON_ATTRS = {
         allow_files = True,
     ),
     "deps": attr.label_list(),
-    "_lcov_merger": attr.label(
-        default = configuration_field(fragment = "coverage", name = "output_generator"),
-        cfg = "exec",
-    ),
 }
 
 def _my_library_impl(ctx):