Ensure compatibility with CMake 3.10

This fixes some CMake-3.12+-isms, like `list(JOIN ...)` and setting link
properties on OBJECT libraries.

PiperOrigin-RevId: 265033725
Change-Id: I0ee1ec0e1b1097ea8226ad6fdeff794a97c2881b

.bazelci/presubmit.yml

@@ -1,5 +1,8 @@
 ---
 tasks:
   ubuntu1804:
+    shell_commands:
+    - apt-get update && apt-get install libcap-dev
+    - pip3 install absl-py clang
     build_targets:
     - "..."

CMakeLists.txt

@@ -38,7 +38,7 @@ configure_file(cmake/libcap_capability.h.in
 
 # Library with basic project settings. The empty file is there to be able to
 # define header-only libraries without cumbersome target_sources() hacks.
-file(TOUCH ${SAPI_BINARY_DIR}/sapi_base_force_cxx_linkage.cc)
+file(WRITE ${SAPI_BINARY_DIR}/sapi_base_force_cxx_linkage.cc "")
 add_library(sapi_base STATIC
   "${SAPI_BINARY_DIR}/sapi_base_force_cxx_linkage.cc"
 )

cmake/SapiBuildDefs.cmake

@@ -102,7 +102,7 @@ function(add_sapi_library)
   set(_sapi_bin "${_sapi_NAME}.bin")
   set(_sapi_force_cxx_linkage
     "${CMAKE_CURRENT_BINARY_DIR}/${_sapi_bin}_force_cxx_linkage.cc")
-  file(TOUCH "${_sapi_force_cxx_linkage}")
+  file(WRITE "${_sapi_force_cxx_linkage}" "")
   add_executable("${_sapi_bin}" "${_sapi_force_cxx_linkage}")
   # TODO(cblichmann): Use target_link_options on CMake >= 3.13
   target_link_libraries("${_sapi_bin}" PRIVATE
@@ -123,12 +123,12 @@ function(add_sapi_library)
   endif()
 
   # Interface
-  list(JOIN _sapi_FUNCTIONS "," _sapi_funcs)
+  list_join(_sapi_FUNCTIONS "," _sapi_funcs)
   foreach(src IN LISTS _sapi_INPUTS)
     get_filename_component(src "${src}" ABSOLUTE)
     list(APPEND _sapi_full_inputs "${src}")
   endforeach()
-  list(JOIN _sapi_full_inputs "," _sapi_full_inputs)
+  list_join(_sapi_full_inputs "," _sapi_full_inputs)
   if(NOT _sapi_NOEMBED)
     set(_sapi_embed_dir "${CMAKE_CURRENT_BINARY_DIR}")
     set(_sapi_embed_name "${_sapi_NAME}")
@@ -152,7 +152,7 @@ function(add_sapi_library)
   if(NOT _sapi_SOURCES)
     set(_sapi_force_cxx_linkage
       "${CMAKE_CURRENT_BINARY_DIR}/${_sapi_NAME}_force_cxx_linkage.cc")
-    file(TOUCH "${_sapi_force_cxx_linkage}")
+    file(WRITE "${_sapi_force_cxx_linkage}" "")
     list(APPEND _sapi_SOURCES "${_sapi_force_cxx_linkage}")
   endif()
   add_library("${_sapi_NAME}" STATIC

cmake/SapiUtil.cmake

@@ -35,6 +35,16 @@ function(create_directory_symlink SOURCE DESTINATION)
   endif()
 endfunction()
 
+# Implements list(JOIN ...) for CMake < 3.12.
+function(list_join LIST SEP OUTPUT)
+  foreach(item IN LISTS ${LIST})
+    set(_concat "${_concat}${SEP}${item}")
+  endforeach()
+  string(LENGTH "${SEP}" _len)
+  string(SUBSTRING "${_concat}" ${_len} -1 _concat)
+  set(${OUTPUT} "${_concat}" PARENT_SCOPE)
+endfunction()
+
 # Helper function that behaves just like Protobuf's protobuf_generate_cpp(),
 # except that it strips import paths. This is necessary, because CMake's
 # protobuf rules don't work well with imports across different directories.

cmake/protobuf/Download.cmake

@@ -38,3 +38,5 @@ set(protobuf_WITH_ZLIB OFF CACHE BOOL "")
 
 add_subdirectory("${CMAKE_BINARY_DIR}/protobuf-src/cmake"
                  "${CMAKE_BINARY_DIR}/protobuf-build" EXCLUDE_FROM_ALL)
+get_property(Protobuf_INCLUDE_DIRS TARGET protobuf::libprotobuf
+                                   PROPERTY INCLUDE_DIRECTORIES)

sandboxed_api/examples/stringop/lib/CMakeLists.txt

@@ -23,9 +23,8 @@ add_library(sapi_stringop_params_proto OBJECT
   ${_sapi_stringop_params_pb_h}
 )
 add_library(sapi::stringop_params_proto ALIAS sapi_stringop_params_proto)
-target_link_libraries(sapi_stringop_params_proto
-  PRIVATE sapi::base
-  PUBLIC protobuf::libprotobuf
+target_include_directories(sapi_stringop_params_proto PUBLIC
+  ${Protobuf_INCLUDE_DIRS}
 )
 
 # sandboxed_api/examples/stringop/lib:stringop

sandboxed_api/examples/sum/lib/CMakeLists.txt

@@ -23,9 +23,8 @@ add_library(sapi_sum_params_proto OBJECT
   ${_sapi_sum_params_pb_h}
 )
 add_library(sapi::sum_params_proto ALIAS sapi_sum_params_proto)
-target_link_libraries(sapi_sum_params_proto
-  PRIVATE sapi::base
-  PUBLIC protobuf::libprotobuf
+target_include_directories(sapi_sum_params_proto PUBLIC
+  ${Protobuf_INCLUDE_DIRS}
 )
 
 # sandboxed_api/examples/sum/lib:sum