Attempt to find RE2 via CMake and via pkg-config.

CMakeLists.txt

@@ -15624,6 +15624,7 @@ install(FILES
 )
 install(FILES
     ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules/Findc-ares.cmake
+    ${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules/Findre2.cmake
   DESTINATION ${gRPC_INSTALL_CMAKEDIR}/modules
 )
 

cmake/modules/Findre2.cmake

@@ -0,0 +1,58 @@
+# Copyright 2017 gRPC authors.
+#
+# 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.
+
+find_package(re2 QUIET CONFIG)
+if(re2_FOUND)
+  message(STATUS "Found RE2 via CMake.")
+  return()
+endif()
+
+find_package(PkgConfig REQUIRED)
+# TODO(junyer): Use the IMPORTED_TARGET option whenever CMake 3.6 (or newer)
+# becomes the minimum required: that will take care of the add_library() and
+# set_property() calls; then we can simply alias PkgConfig::RE2 as re2::re2.
+# For now, we can only set INTERFACE_* properties that existed in CMake 3.5.
+pkg_check_modules(RE2 QUIET re2)
+if(RE2_FOUND)
+  set(re2_FOUND "${RE2_FOUND}")
+  add_library(re2::re2 INTERFACE IMPORTED)
+  if(RE2_INCLUDE_DIRS)
+    set_property(TARGET re2::re2 PROPERTY
+                 INTERFACE_INCLUDE_DIRECTORIES "${RE2_INCLUDE_DIRS}")
+  endif()
+  if(RE2_CFLAGS_OTHER)
+    # Filter out the -std flag, which is handled by CMAKE_CXX_STANDARD.
+    # TODO(junyer): Use the FILTER option whenever CMake 3.6 (or newer)
+    # becomes the minimum required: that will allow this to be concise.
+    foreach(flag IN LISTS RE2_CFLAGS_OTHER)
+      if("${flag}" MATCHES "^-std=")
+        list(REMOVE_ITEM RE2_CFLAGS_OTHER "${flag}")
+      endif()
+    endforeach()
+    set_property(TARGET re2::re2 PROPERTY
+                 INTERFACE_COMPILE_OPTIONS "${RE2_CFLAGS_OTHER}")
+  endif()
+  if(RE2_LDFLAGS)
+    set_property(TARGET re2::re2 PROPERTY
+                 INTERFACE_LINK_LIBRARIES "${RE2_LDFLAGS}")
+  endif()
+  message(STATUS "Found RE2 via pkg-config.")
+  return()
+endif()
+
+if(re2_FIND_REQUIRED)
+  message(FATAL_ERROR "Failed to find RE2.")
+elseif(NOT re2_FIND_QUIETLY)
+  message(WARNING "Failed to find RE2.")
+endif()

cmake/re2.cmake

@@ -45,13 +45,9 @@ if(gRPC_RE2_PROVIDER STREQUAL "module")
     set(gRPC_INSTALL FALSE)
   endif()
 elseif(gRPC_RE2_PROVIDER STREQUAL "package")
-  find_package(re2 REQUIRED CONFIG)
-
+  find_package(re2 REQUIRED)
   if(TARGET re2::re2)
     set(_gRPC_RE2_LIBRARIES re2::re2)
-  else()
-    set(_gRPC_RE2_LIBRARIES ${RE2_LIBRARIES})
   endif()
-  set(_gRPC_RE2_INCLUDE_DIR ${RE2_INCLUDE_DIRS})
   set(_gRPC_FIND_RE2 "if(NOT re2_FOUND)\n  find_package(re2)\nendif()")
 endif()

templates/CMakeLists.txt.template

@@ -706,6 +706,7 @@
   )
   install(FILES
       <%text>${CMAKE_CURRENT_SOURCE_DIR}</%text>/cmake/modules/Findc-ares.cmake
+      <%text>${CMAKE_CURRENT_SOURCE_DIR}</%text>/cmake/modules/Findre2.cmake
     DESTINATION <%text>${gRPC_INSTALL_CMAKEDIR}</%text>/modules
   )