Use custom abseil with bazel (#1172)

.github/workflows/ci.yml

@@ -150,6 +150,28 @@ jobs:
     - name: run tests
       run: ./ci/do_ci.sh bazel.test
 
+  bazel_with_abseil:
+    name: Bazel with external abseil
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: 'recursive'
+    - name: Mount Bazel Cache
+      uses: actions/cache@v2
+      env:
+        cache-name: bazel_cache
+      with:
+        path: /home/runner/.cache/bazel
+        key: bazel_test
+    - name: setup
+      run: |
+        sudo ./ci/setup_thrift.sh dependencies_only
+        sudo ./ci/setup_ci_environment.sh
+        sudo ./ci/install_bazelisk.sh
+    - name: run tests
+      run: ./ci/do_ci.sh bazel.with_abseil
+
   bazel_valgrind:
     name: Bazel valgrind
     runs-on: ubuntu-latest

CHANGELOG.md

@@ -17,6 +17,7 @@ Increment the:
 
 * [SDK] Add LogLevel to internal_log ([#1147](https://github.com/open-telemetry/opentelemetry-cpp/pull/1147))
 * [API/SDK] Logger: Propagating resources through LoggerProvider ([#1154](https://github.com/open-telemetry/opentelemetry-cpp/pull/1154))
+* [API]: Allow to use external abseil for bazel targets ([#1172](https://github.com/open-telemetry/opentelemetry-cpp/pull/1172))
 
 ## [1.1.1] 2021-12-20
 

api/BUILD

@@ -12,11 +12,34 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
+
 package(default_visibility = ["//visibility:public"])
 
+bool_flag(
+    name = "with_abseil",
+    build_setting_default = False,
+)
+
 cc_library(
     name = "api",
     hdrs = glob(["include/**/*.h"]),
+    defines = select({
+        ":with_external_abseil": ["HAVE_ABSEIL"],
+        "//conditions:default": [],
+    }),
     strip_include_prefix = "include",
     tags = ["api"],
+    deps = select({
+        ":with_external_abseil": [
+            "@com_google_absl//absl/base",
+            "@com_google_absl//absl/types:variant",
+        ],
+        "//conditions:default": [],
+    }),
+)
+
+config_setting(
+    name = "with_external_abseil",
+    flag_values = {":with_abseil": "true"},
 )

api/include/opentelemetry/nostd/variant.h

@@ -47,9 +47,9 @@ OPENTELEMETRY_END_NAMESPACE
 #  endif
 
 #  ifdef HAVE_ABSEIL
-#    include <absl/types/variant.h>
+#    include "absl/types/variant.h"
 #  else
-#    include "./absl/types/variant.h"
+#    include "./internal/absl/types/variant.h"
 #  endif
 
 #  ifdef _MSC_VER

bazel/repository.bzl

@@ -28,6 +28,17 @@ def opentelemetry_cpp_deps():
         ],
     )
 
+    # Load abseil dependency(optional)
+    maybe(
+        http_archive,
+        name = "com_google_absl",
+        sha256 = "dd7db6815204c2a62a2160e32c55e97113b0a0178b2f090d6bab5ce36111db4b",
+        strip_prefix = "abseil-cpp-20210324.0",
+        urls = [
+            "https://github.com/abseil/abseil-cpp/archive/20210324.0.tar.gz",
+        ],
+    )
+
     # Load gRPC dependency
     maybe(
         http_archive,

ci/do_ci.sh

@@ -162,6 +162,10 @@ elif [[ "$1" == "bazel.test" ]]; then
   bazel $BAZEL_STARTUP_OPTIONS build $BAZEL_OPTIONS //...
   bazel $BAZEL_STARTUP_OPTIONS test $BAZEL_TEST_OPTIONS //...
   exit 0
+elif [[ "$1" == "bazel.with_abseil" ]]; then
+  bazel $BAZEL_STARTUP_OPTIONS build $BAZEL_OPTIONS --//api:with_abseil=true //...
+  bazel $BAZEL_STARTUP_OPTIONS test $BAZEL_TEST_OPTIONS --//api:with_abseil=true //...
+  exit 0
 elif [[ "$1" == "bazel.macos.test" ]]; then
   bazel $BAZEL_STARTUP_OPTIONS build $BAZEL_MACOS_OPTIONS //...
   bazel $BAZEL_STARTUP_OPTIONS test $BAZEL_MACOS_TEST_OPTIONS //...

docs/dependencies.md

@@ -18,7 +18,7 @@ Both these dependencies are listed here:
 - [API](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/api) & [SDK](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/sdk):
   - Uses Standard C++ library for latest features (std::string_view, std::variant, std::span, std::shared_ptr, std::unique_ptr) with  C++14/17/20 compiler if `WITH_STL` cmake option is enabled or `HAVE_CPP_STDLIB` macro is defined. License: `GNU General Public License`
     - For C++11/14/17 compilers, fallback to gsl::span if [GSL C++ library](https://github.com/microsoft/GSL) is installed. License: `MIT License`
-  - Uses Abseil C++ Library for `absl::variant` as default `nostd::variant` if `WITH_ABSEIL` cmake option is enabled. License: `Apache License 2.0`
+  - Uses Abseil C++ Library for `absl::variant` as default `nostd::variant` if `WITH_ABSEIL` cmake option or  `--@io_opentelemetry_cpp/api:with_abseil=true` (aka `--//api:with_abseil=true`) bazel option is enabled. License: `Apache License 2.0`
 
 - [OTLP/HTTP+JSON](https://github.com/open-telemetry/opentelemetry-cpp/tree/v1.0.0-rc1/exporters/otlp) exporter:
   - [protobuf](https://github.com/protocolbuffers/protobuf):  Library to serialize structured data.

examples/otlp/README.md

@@ -57,7 +57,9 @@ gRPC internally uses a different version of Abseil than OpenTelemetry C++ SDK.
 
 One option to optimize your code is to build the SDK with system-provided
 Abseil library. If you are using CMake, then `-DWITH_ABSEIL=ON` may be passed
-during the build of SDK to reuse the same Abseil library as gRPC.
+during the build of SDK to reuse the same Abseil library as gRPC. If you are
+using Bazel, then `--@io_opentelemetry_cpp/api:with_abseil=true` may be passed
+to reuse your Abseil library in your project.
 
 If you do not want to pursue the above option, and in case if you run into
 conflict between Abseil library and OpenTelemetry C++ `absl::variant`