Initial set of files.

The make install target is not working for .proto files, but otherwise
it seems to work.

1 files changed, 207 insertions, 0 deletions

diff --git a/cmake/FindProtobufTargets.cmake b/cmake/FindProtobufTargets.cmake
new file mode 100644
index 000000000000..db260280d3cd
--- /dev/null
+++ b/cmake/FindProtobufTargets.cmake
@@ -0,0 +1,207 @@
+# ~~~
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ~~~
+
+#[=======================================================================[.rst:
+FindProtobufTargets
+-------------------
+
+A module to use `Protobuf` with less complications.
+
+Using ``find_package(Protobuf)`` should be simple, but it is not.
+
+CMake provides a ``FindProtobuf`` module. Unfortunately it does not generate
+`protobuf::*` targets until CMake-3.9, and `protobuf::protoc` does not
+appear until CMake-3.10.
+
+The CMake-config files generated by `protobuf` always create these targets,
+but on some Linux distributions (e.g. Fedora>=29, and openSUSE-Tumbleweed) there
+are system packages for protobuf, but these packages are installed without the
+CMake-config files. One must either use the ``FindProtobuf`` module, find the
+libraries via `pkg-config`, or find the libraries manually.
+
+When the CMake-config files are installed they produce the same targets as
+recent versions of ``FindProtobuf``. However, they do not produce the
+`Protobuf_LIBRARY`, `Protobuf_INCLUDE_DIR`, etc. that are generated by the
+module. Furthermore, the `protobuf::protoc` library is not usable when loaded
+from the CMake-config files: its ``IMPORTED_LOCATION`` variable is not defined.
+
+This module is designed to provide a single, uniform, ``find_package()``
+module that always produces the same outputs:
+
+- It always generates the ``protobuf::*`` targets.
+- It always defines ``ProtobufTargets_FOUND`` and ``ProtobufTargets_VERSION``.
+- It *prefers* using the CMake config files if they are available.
+- It fallsback on the ``FindProtobuf`` module if the config files are not found.
+- It populates any missing targets and their properties.
+
+The following :prop_tgt:`IMPORTED` targets are defined:
+
+``protobuf::libprotobuf``
+  The protobuf library.
+``protobuf::libprotobuf-lite``
+  The protobuf lite library.
+``protobuf::libprotoc``
+  The protoc library.
+``protobuf::protoc``
+  The protoc compiler.
+
+Example:
+
+.. code-block:: cmake
+
+  find_package(ProtobufTargets REQUIRED)
+  add_executable(bar bar.cc)
+  target_link_libraries(bar PRIVATE protobuf::libprotobuf)
+
+#]=======================================================================]
+
+if (protobuf_DEBUG)
+    message(STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "protobuf_USE_STATIC_LIBS = ${protobuf_USE_STATIC_LIBS}"
+                   " ProtobufTargets = ${ProtobufTargets_FOUND}")
+endif ()
+
+# Always load thread support, even on Windows.
+find_package(Threads REQUIRED)
+
+# First try to use the ``protobufConfig.cmake`` or ``protobuf-config.cmake``
+# file if it was installed. This is common on systems (or package managers)
+# where protobuf was compiled and installed with `CMake`. Note that on Linux
+# this *must* be all lowercase ``protobuf``, while on Windows it does not
+# matter.
+find_package(protobuf CONFIG)
+
+if (protobuf_DEBUG)
+    message(STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "protobuf_FOUND = ${protobuf_FOUND}"
+                   " protobuf_VERSION = ${protobuf_VERSION}")
+endif ()
+
+if (protobuf_FOUND)
+    set(ProtobufTargets_FOUND 1)
+    set(ProtobufTargets_VERSION ${protobuf_VERSION})
+    if (protobuf_DEBUG)
+        message(
+            STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "ProtobufTargets_FOUND = ${ProtobufTargets_FOUND}"
+                   " ProtobufTargets_VERSION = ${ProtobufTargets_VERSION}")
+    endif ()
+else()
+    find_package(Protobuf QUIET)
+    if (Protobuf_FOUND)
+        set(ProtobufTargets_FOUND 1)
+        set(ProtobufTargets_VERSION ${Protobuf_VERSION})
+
+        if (NOT TARGET protobuf::libprotobuf)
+            add_library(protobuf::libprotobuf INTERFACE IMPORTED)
+            set_property(TARGET protobuf::libprotobuf
+                         PROPERTY INTERFACE_INCLUDE_DIRECTORIES
+                                  ${Protobuf_INCLUDE_DIR})
+            set_property(TARGET protobuf::libprotobuf
+                         APPEND
+                         PROPERTY INTERFACE_LINK_LIBRARIES ${Protobuf_LIBRARY}
+                                  Threads::Threads)
+        endif ()
+
+        if (NOT TARGET protobuf::libprotobuf-lite)
+            add_library(protobuf::libprotobuf-lite INTERFACE IMPORTED)
+            set_property(TARGET protobuf::libprotobuf-lite
+                         PROPERTY INTERFACE_INCLUDE_DIRECTORIES
+                                  ${Protobuf_INCLUDE_DIR})
+            set_property(TARGET protobuf::libprotobuf-lite
+                         APPEND
+                         PROPERTY INTERFACE_LINK_LIBRARIES
+                                  ${Protobuf_LITE_LIBRARY} Threads::Threads)
+        endif ()
+
+        if (NOT TARGET protobuf::libprotoc)
+            add_library(protobuf::libprotoc INTERFACE IMPORTED)
+            set_property(TARGET protobuf::libprotoc
+                         PROPERTY INTERFACE_INCLUDE_DIRECTORIES
+                                  ${Protobuf_INCLUDE_DIR})
+            set_property(TARGET protobuf::libprotoc
+                         APPEND
+                         PROPERTY INTERFACE_LINK_LIBRARIES
+                                  ${Protobuf_PROTOC_LIBRARY} Threads::Threads)
+        endif ()
+    endif ()
+endif ()
+
+if (protobuf_DEBUG)
+    message(STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "ProtobufTargets_FOUND = ${ProtobufTargets_FOUND}"
+                   " ProtobufTargets_VERSION = ${ProtobufTargets_VERSION}")
+endif ()
+
+# We also should try to find the protobuf C++ plugin for the protocol buffers
+# compiler.
+if (ProtobufTargets_FOUND AND NOT TARGET protobuf::protoc)
+    add_executable(protobuf::protoc IMPORTED)
+
+    # Discover the protoc compiler location.
+    find_program(_protobuf_PROTOC_EXECUTABLE
+                 NAMES protoc
+                 DOC "The Google Protocol Buffers Compiler")
+    if (protobuf_DEBUG)
+        message(
+            STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "ProtobufTargets_FOUND = ${ProtobufTargets_FOUND}"
+                   " ProtobufTargets_VERSION = ${ProtobufTargets_VERSION}"
+                   " EXE = ${_protobuf_PROTOC_EXECUTABLE}")
+    endif ()
+    set_property(TARGET protobuf::protoc
+                 PROPERTY IMPORTED_LOCATION ${_protobuf_PROTOC_EXECUTABLE})
+    set_property(
+        TARGET protobuf::protoc
+        PROPERTY IMPORTED_LOCATION_DEBUG ${_protobuf_PROTOC_EXECUTABLE})
+    set_property(TARGET protobuf::protoc
+                 PROPERTY IMPORTED_LOCATION_RELEASE
+                          ${_protobuf_PROTOC_EXECUTABLE})
+    unset(_protobuf_PROTOC_EXECUTABLE)
+
+    if (protobuf_DEBUG)
+        get_target_property(_protobuf_PROTOC_EXECUTABLE protobuf::protoc
+                            IMPORTED_LOCATION)
+        message(
+            STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "LOCATION=${_protobuf_PROTOC_EXECUTABLE}")
+    endif ()
+endif ()
+
+if (protobuf_DEBUG)
+    message(STATUS "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                   "ProtobufTargets_FOUND = ${ProtobufTargets_FOUND}"
+                   " ProtobufTargets_VERSION = ${ProtobufTargets_VERSION}")
+    if (ProtobufTargets_FOUND)
+        foreach (_target
+                 protobuf::libprotobuf
+                 protobuf::libprotobuf-lite
+                 protobuf::libprotoc)
+            if (NOT TARGET ${_target})
+                message(
+                    STATUS
+                        "[ ${CMAKE_CURRENT_LIST_FILE}:${CMAKE_CURRENT_LIST_LINE} ] "
+                        "target=${_target} is NOT a target")
+            endif ()
+        endforeach ()
+        unset(_target)
+    endif ()
+endif ()
+
+find_package_handle_standard_args(ProtobufTargets
+                                  REQUIRED_VARS
+                                  ProtobufTargets_FOUND
+                                  ProtobufTargets_VERSION)