Port collect_cc_coverage.sh to C++

cc/private/coverage/BUILD.bazel

@@ -1,15 +1,46 @@
+load("@rules_cc//cc:cc_binary.bzl", "cc_binary")
+load("@rules_cc//cc:cc_library.bzl", "cc_library")
+
 config_setting(
     name = "incompatible_use_native_collect_cc_coverage_enabled",
     flag_values = {
         "//cc/settings:incompatible_use_native_collect_cc_coverage": "true",
     },
 )
 
+config_setting(
+    name = "experimental_use_cc_coverage_collector_enabled",
+    flag_values = {
+        "//cc/settings:experimental_use_cc_coverage_collector": "true",
+    },
+)
+
+cc_library(
+    name = "coverage_utils",
+    srcs = ["coverage_utils.cc"],
+    hdrs = ["coverage_utils.h"],
+)
+
+cc_binary(
+    name = "collect_coverage",
+    srcs = ["collect_coverage.cc"],
+    visibility = ["//visibility:public"],
+    deps = [":coverage_utils"],
+)
+
+alias(
+    name = "collector",
+    actual = select({
+        ":experimental_use_cc_coverage_collector_enabled": ":collect_coverage",
+        "//conditions:default": "collect_cc_coverage.sh",
+    }),
+)
+
 filegroup(
     name = "collect_cc_coverage",
     srcs = select({
         ":incompatible_use_native_collect_cc_coverage_enabled": ["@bazel_tools//tools/test:collect_cc_coverage"],
-        "//conditions:default": ["collect_cc_coverage.sh"],
+        "//conditions:default": [":collector"],
     }),
     visibility = ["//visibility:public"],
 )

cc/private/coverage/collect_coverage.cc

@@ -0,0 +1,80 @@
+// Copyright 2016 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.
+
+/// @file collect_coverage.cc
+/// @brief Entry point that collects code coverage data for C++ sources after
+///        tests are executed.
+///
+/// This program is the native reimplementation of the historical
+/// @c collect_cc_coverage.sh shell script that ships with Bazel. It runs on
+/// Linux, macOS, and Windows. All non-trivial work is delegated to the
+/// helpers in @c coverage_utils.h so that the dispatch logic here reads like
+/// the shell script's @c main function.
+///
+/// The following environment variables are consumed:
+///  - @c COVERAGE_DIR           Directory containing coverage metadata files.
+///  - @c COVERAGE_MANIFEST      Location of the instrumented file manifest.
+///  - @c COVERAGE_GCOV_PATH     Location of @c gcov (set by the TestRunner).
+///  - @c COVERAGE_GCOV_OPTIONS  Additional options to pass to @c gcov.
+///  - @c ROOT                   Directory from which coverage collection was
+///                              invoked (contains @c .gcno files).
+///  - @c VERBOSE_COVERAGE       Print debug information when non-empty.
+///  - @c LLVM_PROFDATA          Path to @c llvm-profdata.
+///  - @c LLVM_COV               Path to @c llvm-cov.
+///  - @c GENERATE_LLVM_LCOV     When @c "1", emit lcov instead of profdata.
+///  - @c BAZEL_CC_COVERAGE_TOOL The coverage tool to dispatch to. Defaults to
+///                              @c GCOV; overridden to @c LLVM_LCOV or
+///                              @c PROFDATA when @c *.profraw files are found.
+
+#include <filesystem>
+#include <iostream>
+#include <string>
+
+#include "cc/private/coverage/coverage_utils.h"
+
+int main() {
+  namespace fs = std::filesystem;
+  using bazel_coverage::GcovCoverage;
+  using bazel_coverage::GetEnv;
+  using bazel_coverage::LlvmCoverageLcov;
+  using bazel_coverage::LlvmCoverageProfdata;
+  using bazel_coverage::RequireEnv;
+  using bazel_coverage::SetVerbose;
+  using bazel_coverage::UsesLlvm;
+
+  SetVerbose(GetEnv("VERBOSE_COVERAGE").has_value());
+
+  fs::path coverage_dir = RequireEnv("COVERAGE_DIR");
+
+  // If LLVM coverage data is present, override the default GCOV tool with the
+  // appropriate LLVM flow. Matches the shell script's `uses_llvm` branch.
+  std::string tool = GetEnv("BAZEL_CC_COVERAGE_TOOL").value_or("GCOV");
+  if (UsesLlvm(coverage_dir)) {
+    tool = GetEnv("GENERATE_LLVM_LCOV").value_or("") == "1" ? "LLVM_LCOV"
+                                                            : "PROFDATA";
+  }
+
+  if (tool == "GCOV") {
+    return GcovCoverage(coverage_dir / "_cc_coverage.gcov");
+  }
+  if (tool == "PROFDATA") {
+    return LlvmCoverageProfdata(coverage_dir / "_cc_coverage.profdata");
+  }
+  if (tool == "LLVM_LCOV") {
+    return LlvmCoverageLcov(coverage_dir / "_cc_coverage.dat");
+  }
+
+  std::cerr << "Coverage tool " << tool << " not supported\n";
+  return 1;
+}