✨ add bazel build for grpc example (open-telemetry#910)

WORKSPACE

@@ -29,6 +29,7 @@ load("@com_github_grpc_grpc//bazel:grpc_extra_deps.bzl", "grpc_extra_deps")
 
 grpc_extra_deps()
 
+load("@com_github_grpc_grpc//bazel:cc_grpc_library.bzl", "cc_grpc_library")
 load("@upb//bazel:workspace_deps.bzl", "upb_deps")
 
 upb_deps()

examples/grpc/BUILD

@@ -0,0 +1,60 @@
+package(default_visibility = ["//visibility:public"])
+
+load("@rules_proto//proto:defs.bzl", "proto_library")
+load("@com_github_grpc_grpc//bazel:cc_grpc_library.bzl", "cc_grpc_library")
+
+proto_library(
+    name = "messages_proto",
+    srcs = ["protos/messages.proto"],
+)
+
+cc_proto_library(
+    name = "messages_cc_proto",
+    deps = [":messages_proto"],
+)
+
+cc_grpc_library(
+    name = "messages_cc_grpc",
+    srcs = [":messages_proto"],
+    grpc_only = True,
+    deps = [":messages_cc_proto"],
+)
+
+cc_library(
+    name = "tracer_common",
+    srcs = ["tracer_common.h"],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "//exporters/ostream:ostream_span_exporter",
+    ],
+)
+
+cc_binary(
+    name = "client_grpc",
+    srcs = [
+        "client.cpp",
+    ],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "messages_cc_grpc",
+        ":tracer_common",
+        "//api",
+        "//sdk/src/trace",
+        "@com_github_grpc_grpc//:grpc++",
+    ],
+)
+
+cc_binary(
+    name = "server_grpc",
+    srcs = [
+        "server.cpp",
+    ],
+    defines = ["BAZEL_BUILD"],
+    deps = [
+        "messages_cc_grpc",
+        ":tracer_common",
+        "//api",
+        "//sdk/src/trace",
+        "@com_github_grpc_grpc//:grpc++",
+    ],
+)

examples/grpc/client.cpp

@@ -2,7 +2,11 @@
 // ambiguity with `nostd::variant` if compiled with Visual Studio 2015. Other
 // modern compilers are unaffected.
 #include <grpcpp/grpcpp.h>
+#ifdef BAZEL_BUILD
+#include "examples/grpc/protos/messages.grpc.pb.h"
+#else
 #include "messages.grpc.pb.h"
+#endif
 
 #include "tracer_common.h"
 #include <iostream>

examples/grpc/server.cpp

@@ -1,4 +1,8 @@
+#ifdef BAZEL_BUILD
+#include "examples/grpc/protos/messages.grpc.pb.h"
+#else
 #include "messages.grpc.pb.h"
+#endif
 #include "tracer_common.h"
 #include "opentelemetry/trace/span_context_kv_iterable_view.h"