From 5534dd2fcb539006163a875fe5258a6e7120f52d Mon Sep 17 00:00:00 2001
From: Ulf Adams <ulfjack@google.com>
Date: Tue, 17 Apr 2018 10:36:41 +0200
Subject: [PATCH] Prototype support for llvm coverage

https://clang.llvm.org/docs/SourceBasedCodeCoverage.html

Usage:
BAZEL_USE_LLVM_NATIVE_COVERAGE=1 GCOV=llvm-profdata-3.9 CC=clang-3.9 bazel coverage --instrumentation_filter=src/main/cpp src/test/cpp:all
---
 tools/cpp/cc_configure.bzl      |  3 ++-
 tools/cpp/unix_cc_configure.bzl | 11 ++++++++---
 tools/test/collect_coverage.sh  | 17 ++++++++++++-----
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/tools/cpp/cc_configure.bzl b/tools/cpp/cc_configure.bzl
index cf121260f47563..88c16cca1d5922 100644
--- a/tools/cpp/cc_configure.bzl
+++ b/tools/cpp/cc_configure.bzl
@@ -53,6 +53,7 @@ cc_autoconf = repository_rule(
         "BAZEL_TARGET_LIBC",
         "BAZEL_TARGET_SYSTEM",
         "BAZEL_USE_CPP_ONLY_TOOLCHAIN",
+        "BAZEL_USE_LLVM_NATIVE_COVERAGE",
         "BAZEL_VC",
         "BAZEL_VS",
         "CC",
@@ -64,9 +65,9 @@ cc_autoconf = repository_rule(
         "GCOV",
         "HOMEBREW_RUBY_PATH",
         "NO_WHOLE_ARCHIVE_OPTION",
+        "SYSTEMROOT",
         "USE_DYNAMIC_CRT",
         "USE_MSVC_WRAPPER",
-        "SYSTEMROOT",
         "VS90COMNTOOLS",
         "VS100COMNTOOLS",
         "VS110COMNTOOLS",
diff --git a/tools/cpp/unix_cc_configure.bzl b/tools/cpp/unix_cc_configure.bzl
index a74edf80b0fc27..bcfe2569775782 100644
--- a/tools/cpp/unix_cc_configure.bzl
+++ b/tools/cpp/unix_cc_configure.bzl
@@ -338,8 +338,13 @@ def get_env(repository_ctx):
     return ""
 
 
-def _coverage_feature(darwin):
-  if darwin:
+def _coverage_feature(repository_ctx, darwin):
+  use_llvm_cov = "1" == get_env_var(
+      repository_ctx,
+      "BAZEL_USE_LLVM_NATIVE_COVERAGE",
+      default="0",
+      enable_warning=False)
+  if darwin or use_llvm_cov:
     compile_flags = """flag_group {
         flag: '-fprofile-instr-generate'
         flag: '-fcoverage-mapping'
@@ -450,7 +455,7 @@ def configure_unix_toolchain(repository_ctx, cpu_value, overriden_tools):
       "%{opt_content}": _build_crosstool(opt_content, "    "),
       "%{dbg_content}": _build_crosstool(dbg_content, "    "),
       "%{cxx_builtin_include_directory}": "",
-      "%{coverage}": _coverage_feature(darwin),
+      "%{coverage}": _coverage_feature(repository_ctx, darwin),
       "%{msvc_env_tmp}": "",
       "%{msvc_env_path}": "",
       "%{msvc_env_include}": "",
diff --git a/tools/test/collect_coverage.sh b/tools/test/collect_coverage.sh
index b9579cac993739..20410a6ccc6478 100755
--- a/tools/test/collect_coverage.sh
+++ b/tools/test/collect_coverage.sh
@@ -88,6 +88,7 @@ fi
 if [[ "$COVERAGE_LEGACY_MODE" ]]; then
   export GCOV_PREFIX_STRIP=3
   export GCOV_PREFIX="${COVERAGE_DIR}"
+  export LLVM_PROFILE_FILE="${COVERAGE_DIR}/%h-%p-%m.profraw"
 fi
 
 cd "$TEST_SRCDIR/$TEST_WORKSPACE"
@@ -107,11 +108,17 @@ fi
 
 cd $ROOT
 
-# If LCOV_MERGER is not set, use the legacy, awful, C++-only method to convert
-# coverage files.
-# NB: This is here just so that we don't regress. Do not add support for new
-# coverage features here. Implement it instead properly in LcovMerger.
-if [[ "$COVERAGE_LEGACY_MODE" ]]; then
+USES_LLVM_COV=
+if stat --printf='' "${COVERAGE_DIR}"/*.profraw 2>/dev/null; then
+  USES_LLVM_COV=1
+fi
+
+if [[ "$USES_LLVM_COV" ]]; then
+  "${GCOV}" merge -output "${COVERAGE_OUTPUT_FILE}" "${COVERAGE_DIR}"/*.profraw
+  exit $TEST_STATUS
+
+# If LCOV_MERGER is not set, use the legacy C++-only method to convert coverage files.
+elif [[ "$COVERAGE_LEGACY_MODE" ]]; then
   cat "${COVERAGE_MANIFEST}" | grep ".gcno$" | while read path; do
     mkdir -p "${COVERAGE_DIR}/$(dirname ${path})"
     cp "${ROOT}/${path}" "${COVERAGE_DIR}/${path}"