cleanup(otel): bazel flag is obsolete (#14416)

.bazelrc

@@ -52,7 +52,6 @@ common:macos --repo_env=BAZEL_NO_APPLE_CPP_TOOLCHAIN=1
 test --test_env=GTEST_SHUFFLE --test_env=GTEST_RANDOM_SEED
 
 # By default, build the library with OpenTelemetry
-build --@io_opentelemetry_cpp//api:with_abseil
 build --//:enable_opentelemetry
 
 # Don't show warnings when building external dependencies. This still shows

CHANGELOG.md

@@ -6,10 +6,32 @@ breaking changes in the upcoming 3.x release. This release is scheduled for
 
 ## v2.27.0 - TBD
 
-* We have stopped testing on CentOS 7, Debian 10 (Buster), and RockyLinux 8 as
+- We have stopped testing on CentOS 7, Debian 10 (Buster), and RockyLinux 8 as
   these distros are EOL or in some form of "security only" support period.
   Note that we used CentOS 7 as a proxy for testing RedHat Enterprise Linux 7.
 
+### [OpenTelemetry](/google/cloud/opentelemetry/README.md)
+
+#### Bazel
+
+The `--io_opentelemetry_cpp//api:with_abseil` flag was marked as deprecated in
+OpenTelemetry v1.16.0. It may be removed in future versions.
+
+In previous versions of `opentelemetry-cpp`, this flag was required for
+compatibility with Abseil. It is no longer necessary, as `opentelemetry-cpp` is
+compiled with Abseil by default.
+
+We have stopped using the flag to validate Bazel build configurations with
+OpenTelemetry tracing enabled.
+
+If you are building `google-cloud-cpp` with `opentelemetry-cpp` < v1.16.0, you
+will need to supply the flag for compatibility with Abseil. The following can be
+added to your `.bazelrc` file.
+
+```bash
+build --@io_opentelemetry_cpp//api:with_abseil
+```
+
 ## v2.26.0 - 2024-07
 
 ### BREAKING TESTING CHANGES

ci/verify_current_targets/.bazelrc

@@ -35,7 +35,3 @@ common --noenable_bzlmod
 # TODO(#13311) - remove once gRPC works with Bazel v7 or when gRPC stops using
 #     `apple_rules`.
 common:macos --repo_env=BAZEL_NO_APPLE_CPP_TOOLCHAIN=1
-
-# Build OpenTelemetry assuming Abseil exists. Otherwise we get symbol conflicts
-# between the Abseil implementation and the copy in OTel.
-build --@io_opentelemetry_cpp//api:with_abseil

doc/packaging.md

@@ -126,9 +126,9 @@ quickstart guides also cover this use-case.
 `google-cloud-cpp` also has an **optional** dependency on the following
 libraries:
 
-| Library                           | Minimum version | Description                |
-| --------------------------------- | --------------- | -------------------------- |
-| [OpenTelemetry][opentelemetry-gh] | 1.9.1           | An observability framework |
+| Library                           | Minimum version | Description                    |
+| --------------------------------- | --------------- | ------------------------------ |
+| [OpenTelemetry][opentelemetry-gh] | 1.9.1           | An observability framework[^7] |
 
 Note that these libraries may also depend on other libraries. The following
 instructions include steps to install these indirect dependencies too.
@@ -1531,6 +1531,9 @@ cmake --build cmake-out --target install
     workaround conflicts between system pre-processor macros and symbols used in
     the Protobuf-generated code.
 
+[^7]: See the [OpenTelemetry quickstart][otel-qs] for detailed instructions on how
+    to enable and build this optional dependency.
+
 [abseil-gh]: https://github.com/abseil/abseil-cpp
 [abseil/abseil-cpp#696]: https://github.com/abseil/abseil-cpp/issues/696
 [crc32c-gh]: https://github.com/google/crc32c
@@ -1543,6 +1546,7 @@ cmake --build cmake-out --target install
 [nlohmann-json-gh]: https://github.com/nlohmann/json
 [openssl-gh]: https://github.com/openssl/openssl
 [opentelemetry-gh]: https://github.com/open-telemetry/opentelemetry-cpp
+[otel-qs]: https://github.com/googleapis/google-cloud-cpp/tree/main/google/cloud/opentelemetry/quickstart#opentelemetry-dependency
 [protobuf-gh]: https://github.com/protocolbuffers/protobuf
 [spanner-link]: https://github.com/googleapis/google-cloud-cpp/tree/main/google/cloud/spanner#readme
 [storage-link]: https://github.com/googleapis/google-cloud-cpp/tree/main/google/cloud/storage#readme

google/cloud/BUILD.bazel

@@ -45,17 +45,9 @@ capture_build_info(
 )
 
 config_setting(
-    name = "enable_opentelemetry_valid",
+    name = "enable_opentelemetry",
     flag_values = {
         "//:enable_opentelemetry": "true",
-        "@io_opentelemetry_cpp//api:with_abseil": "true",
-    },
-)
-
-config_setting(
-    name = "disable_opentelemetry",
-    flag_values = {
-        "//:enable_opentelemetry": "false",
     },
 )
 
@@ -70,7 +62,7 @@ cc_library(
     srcs = google_cloud_cpp_common_srcs + ["internal/build_info.cc"],
     hdrs = google_cloud_cpp_common_hdrs,
     defines = select({
-        ":enable_opentelemetry_valid": [
+        ":enable_opentelemetry": [
             # Enable OpenTelemetry features in google-cloud-cpp
             "GOOGLE_CLOUD_CPP_HAVE_OPENTELEMETRY",
         ],
@@ -89,24 +81,6 @@ cc_library(
         ],
         "//conditions:default": [],
     }),
-    target_compatible_with = select(
-        {
-            ":enable_opentelemetry_valid": [],
-            ":disable_opentelemetry": [],
-        },
-        # else, OpenTelemetry is enabled, but with an invalid configuration.
-        no_match_error = """
-
-
-You requested OpenTelemetry support for `google-cloud-cpp`, but OpenTelemetry is
-configured without Abseil support. This configuration will result in ODR
-violations, and possibly build-time errors, as OpenTelemetry redefines Abseil
-symbols in this case, and `google-cloud-cpp` uses Abseil directly too.
-
-To fix this problem, supply the `--@io_opentelemetry_cpp//api:with_abseil` flag
-to your build command, or set this value in your `.bazelrc` file(s).
-""",
-    ),
     visibility = [
         ":__subpackages__",
         "//:__pkg__",
@@ -121,7 +95,7 @@ to your build command, or set this value in your `.bazelrc` file(s).
         "@com_google_absl//absl/types:span",
         "@com_google_absl//absl/types:variant",
     ] + select({
-        ":enable_opentelemetry_valid": [
+        ":enable_opentelemetry": [
             "@io_opentelemetry_cpp//api",
         ],
         "//conditions:default": [],

google/cloud/opentelemetry/quickstart/.bazelrc

@@ -30,5 +30,15 @@ build:macos --host_cxxopt=-std=c++14
 build --experimental_convenience_symlinks=ignore
 
 # Enable OpenTelemetry tracing instrumentation for google-cloud-cpp.
-build --@io_opentelemetry_cpp//api:with_abseil
 build --@google_cloud_cpp//:enable_opentelemetry
+
+# OpenTelemetry versions < v1.16.0 are not compatible with Abseil
+# out-of-the-box. If you are using a version of OpenTelemetry < v1.16.0,
+# uncomment the following configuration:
+#
+# ```
+# build --@io_opentelemetry_cpp//api:with_abseil
+# ```
+#
+# Note that the flag is not required for OpenTelemetry versions >= v1.16.0. In
+# fact, the flag may be removed in future versions of OpenTelemetry.

google/cloud/opentelemetry/quickstart/README.md

@@ -76,18 +76,22 @@ flags when compiling `opentelemetry-cpp`.
 
 ### Details
 
-Note the following two feature flags explicitly set in the `.bazelrc`. Together,
-these flags enable OpenTelemetry tracing instrumentation in `google-cloud-cpp`.
-Without these flags, the above `bazel build ...` command would fail.
+Note the following feature flag explicitly set in the `.bazelrc`. This flag
+enables OpenTelemetry tracing instrumentation in `google-cloud-cpp`.
 
 ```bash
-# Required for OpenTelemetry + Abseil compatibility
-build --@io_opentelemetry_cpp//api:with_abseil
-
 # Enables tracing instrumentation in google-cloud-cpp
 build --@google_cloud_cpp//:enable_opentelemetry
 ```
 
+If you are using an OpenTelemetry version \< v1.16.0, you must also supply the
+following flag for compatibility with Abseil. Without this flag, the above
+`bazel build ...` command will fail.
+
+```bash
+build --@io_opentelemetry_cpp//api:with_abseil
+```
+
 Also note that we explicitly load OpenTelemetry's dependencies in the
 `WORKSPACE.bazel`.
 

google/cloud/testing_util/BUILD.bazel

@@ -45,7 +45,7 @@ cc_library(
         "@com_google_absl//absl/debugging:symbolize",
         "@com_google_googletest//:gtest_main",
     ] + select({
-        "//google/cloud:enable_opentelemetry_valid": [
+        "//google/cloud:enable_opentelemetry": [
             "@io_opentelemetry_cpp//exporters/memory:in_memory_span_exporter",
             "@io_opentelemetry_cpp//sdk/src/trace",
         ],