Exit collect_coverage.sh early if LCOV_MERGER is not set.

src/test/shell/bazel/BUILD

@@ -564,6 +564,15 @@ 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_cc_code_coverage_test",
     srcs = ["bazel_cc_code_coverage_test.sh"],

src/test/shell/bazel/bazel_coverage_starlark_test.sh

@@ -0,0 +1,110 @@
+#!/bin/bash
+#
+# Copyright 2021 The Bazel Authors. All rights reserved.
+#
+# 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 set_up() {
+    touch WORKSPACE
+}
+
+function test_starlark_rule_without_lcov_merger() {
+    cat <<EOF > rules.bzl
+def _impl(ctx):
+    output = ctx.actions.declare_file(ctx.attr.name)
+    ctx.actions.write(output, "", is_executable = True)
+    return [DefaultInfo(executable=output)]
+
+custom_test = rule(
+    implementation = _impl,
+    test = True,
+)
+EOF
+
+    cat <<EOF > BUILD
+load(":rules.bzl", "custom_test")
+
+custom_test(name = "foo_test")
+EOF
+    bazel coverage //:foo_test --combined_report=lcov > $TEST_log \
+        || fail "Coverage run failed but should have succeeded."
+}
+
+function test_starlark_rule_with_custom_lcov_merger() {
+
+    cat <<EOF > lcov_merger.sh
+for var in "\$@"
+do
+    if [[ "\$var" == "--output_file="* ]]; then
+        path="\${var##--output_file=}"
+        mkdir -p "\$(dirname \$path)"
+        echo lcov_merger_called >> \$path
+        exit 0
+    fi
+done
+EOF
+chmod +x lcov_merger.sh
+
+    cat <<EOF > rules.bzl
+def _impl(ctx):
+    output = ctx.actions.declare_file(ctx.attr.name)
+    ctx.actions.write(output, "", is_executable = True)
+    return [DefaultInfo(executable=output)]
+
+custom_test = rule(
+    implementation = _impl,
+    test = True,
+    attrs = {
+        "_lcov_merger": attr.label(default = ":lcov_merger", cfg = "exec"),
+    },
+)
+EOF
+
+    cat <<EOF > BUILD
+load(":rules.bzl", "custom_test")
+
+sh_binary(
+    name = "lcov_merger",
+    srcs = ["lcov_merger.sh"],
+)
+custom_test(name = "foo_test")
+EOF
+
+    bazel coverage --test_output=all //:foo_test --combined_report=lcov > $TEST_log \
+        || fail "Coverage run failed but should have succeeded."
+
+    local coverage_file_path="$( get_coverage_file_path_from_test_log )"
+    cat $coverage_file_path
+    grep "lcov_merger_called"  "$coverage_file_path" \
+        || fail "Coverage report did not contain evidence of custom lcov_merger."
+}
+
+run_suite "test tests"

tools/test/collect_coverage.sh

@@ -30,6 +30,18 @@ if [[ -n "$VERBOSE_COVERAGE" ]]; then
   set -x
 fi
 
+if [[ -z "$LCOV_MERGER" ]]; then
+  # this can happen if a rule returns an InstrumentedFilesInfo (which all do
+  # following 5b216b2) but does not define an _lcov_merger attribute.
+  # Unfortunately, we cannot simply stop this script being called in this case
+  # due to conflicts with how things work within Google.
+  # The file creation is required because TestActionBuilder has already declared
+  # it.
+  # TODO(cmita): Improve this situation so this early-exit isn't required.
+  touch $COVERAGE_OUTPUT_FILE
+  exit 0
+fi
+
 function resolve_links() {
   local name="$1"