Simplify Protobuf configuration

CMakeLists.txt

@@ -114,16 +114,6 @@ option(
     OFF)
 mark_as_advanced(GOOGLE_CLOUD_CPP_INTERNAL_DOCFX)
 
-option(
-    GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND
-    [==[Enable the workarounds for [ctype = CORD] when using Protobuf < v23.
-More details at
-
-https://github.com/googleapis/google-cloud-cpp/blob/main/doc/ctype-cord-workarounds.md
-]==]
-    OFF)
-mark_as_advanced(GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND)
-
 set(GOOGLE_CLOUD_CPP_OVERRIDE_GOOGLEAPIS_URL
     ""
     CACHE

ci/cloudbuild/builds/cmake-oldest-deps.sh

@@ -38,8 +38,7 @@ cmake -GNinja -S . -B cmake-out/build \
   "-DCMAKE_TOOLCHAIN_FILE=${vcpkg_root}/scripts/buildsystems/vcpkg.cmake" \
   "-DVCPKG_MANIFEST_DIR=ci/etc/oldest-deps" \
   "-DVCPKG_FEATURE_FLAGS=versions,manifest" \
-  "-DGOOGLE_CLOUD_CPP_ENABLE=${ENABLED_FEATURES}" \
-  "-DGOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND=ON"
+  "-DGOOGLE_CLOUD_CPP_ENABLE=${ENABLED_FEATURES}"
 
 io::log_h2 "Building"
 cmake --build cmake-out/build

ci/cloudbuild/builds/m32.sh

@@ -35,8 +35,7 @@ readonly ENABLED_FEATURES
 # This is the build to test with -m32, which requires a toolchain file.
 io::run cmake "${cmake_args[@]}" \
   "--toolchain" "${PROJECT_ROOT}/ci/etc/m32-toolchain.cmake" \
-  -DGOOGLE_CLOUD_CPP_ENABLE="${ENABLED_FEATURES}" \
-  -DGOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND=ON
+  -DGOOGLE_CLOUD_CPP_ENABLE="${ENABLED_FEATURES}"
 io::run cmake --build cmake-out
 mapfile -t ctest_args < <(ctest::common_args)
 io::run env -C cmake-out ctest "${ctest_args[@]}" -LE "integration-test"

ci/gha/builds/lib/cmake.sh

@@ -65,9 +65,6 @@ function cmake::vcpkg_args() {
   local args
   args=(
     -DCMAKE_TOOLCHAIN_FILE="${VCPKG_ROOT}/scripts/buildsystems/vcpkg.cmake"
-    # The version of vcpkg we are using ships with Protobuf v21.x, the
-    # workarounds are required until v23.x.
-    -DGOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND=ON
   )
   printf "%s\n" "${args[@]}"
 }

google/cloud/storage/google_cloud_cpp_storage_grpc.cmake

@@ -21,11 +21,6 @@ if (NOT GOOGLE_CLOUD_CPP_STORAGE_ENABLE_GRPC)
     set_target_properties(
         google_cloud_cpp_storage_grpc
         PROPERTIES EXPORT_NAME "google-cloud-cpp::storage_grpc")
-    if (GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND)
-        target_compile_definitions(
-            google_cloud_cpp_storage_grpc
-            INTERFACE GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND)
-    endif ()
     add_library(google_cloud_cpp_storage_protos INTERFACE)
     add_library(google-cloud-cpp::storage_protos ALIAS
                 google_cloud_cpp_storage_protos)
@@ -36,6 +31,31 @@ else ()
     include(GoogleCloudCppLibrary)
     google_cloud_cpp_add_library_protos(storage)
 
+    set(GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND_DEFAULT ON)
+    # Protobuf versions are ... complicated.  Protobuf used to call itself
+    # 3.21.*, 3.20.*, 3.19.*, etc. Then it starts calling itself 22.*, 23.*,
+    # etc. This may change in the future:
+    #
+    # https://github.com/protocolbuffers/protobuf/issues/13103
+    #
+    # Guessing the new version scheme is tempting, but probably unwise.
+    #
+    # In any case, `ctype=CORD` is supported starting in 23.x.
+    if (Protobuf_VERSION VERSION_GREATER "23.x")
+        set(GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND_DEFAULT OFF)
+    endif ()
+    message(GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND_DEFAULT=
+            ${GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND_DEFAULT})
+    option(
+        GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND
+        [==[Enable the workarounds for [ctype = CORD] when using Protobuf < v23.
+    More details at
+
+    https://github.com/googleapis/google-cloud-cpp/blob/main/doc/ctype-cord-workarounds.md
+    ]==]
+        ${GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND_DEFAULT})
+    mark_as_advanced(GOOGLE_CLOUD_CPP_ENABLE_CTYPE_CORD_WORKAROUND)
+
     add_library(
         google_cloud_cpp_storage_grpc # cmake-format: sort
         async/client.cc