Convert googletest and nanopb CMake builds to add_subdirectory (#1522)

* Add a download-only boringssl ExternalProject

Match boringssl version to grpc submodule version

Note: not yet in use

* Split grpc into separate download and build tasks

This allows other external targets to download into the gRPC source tree
before grpc is actually built.

* Convert grpc to an http download

* Build googletest with add_subdirectory

Also:
  * Revert library-name modifications in the abseil-cpp build
  * Move abseil-cpp add_subdirectory build into place

* Build nanopb with add_subdirectory

* Force nanopb first to work around ODR violations

This is a temporary work-around for b/111328563.

4 files changed, 18 insertions, 59 deletions

diff --git a/cmake/FindGMock.cmake b/cmake/FindGMock.cmake
deleted file mode 100644
index 76ce227..0000000
--- a/cmake/FindGMock.cmake
+++ /dev/null
@@ -1,47 +0,0 @@
-# Copyright 2018 Google
-#
-# 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.
-
-include(FindPackageHandleStandardArgs)
-
-find_path(
-  GMOCK_INCLUDE_DIR gmock/gmock.h
-  HINTS ${FIREBASE_INSTALL_DIR}/include
-)
-
-find_library(
-  GMOCK_LIBRARY
-  NAMES gmock
-  HINTS ${FIREBASE_INSTALL_DIR}/lib
-)
-
-find_package_handle_standard_args(
-  gmock
-  DEFAULT_MSG
-  GMOCK_INCLUDE_DIR
-  GMOCK_LIBRARY
-)
-
-if(GMOCK_FOUND)
-  set(GMOCK_INCLUDE_DIRS ${GMOCK_INCLUDE_DIR})
-  set(GMOCK_LIBRARIES ${GMOCK_LIBRARY})
-
-  if (NOT TARGET GMock::GMock)
-    add_library(GMock::GMock UNKNOWN IMPORTED)
-    set_target_properties(
-      GMock::GMock PROPERTIES
-      INTERFACE_INCLUDE_DIRECTORIES ${GMOCK_INCLUDE_DIRS}
-      IMPORTED_LOCATION ${GMOCK_LIBRARY}
-    )
-  endif()
-endif(GMOCK_FOUND)
diff --git a/cmake/external/googletest.cmake b/cmake/external/googletest.cmake
index e2ebafc..32e9a39 100644
--- a/cmake/external/googletest.cmake
+++ b/cmake/external/googletest.cmake
@@ -28,8 +28,8 @@ ExternalProject_Add(
 
   PREFIX ${PROJECT_BINARY_DIR}
 
-  CMAKE_CACHE_ARGS
-    -DCMAKE_INSTALL_PREFIX:STRING=${FIREBASE_INSTALL_DIR}
-
+  CONFIGURE_COMMAND ""
+  BUILD_COMMAND ""
+  INSTALL_COMMAND ""
   TEST_COMMAND ""
 )
diff --git a/cmake/external/nanopb.cmake b/cmake/external/nanopb.cmake
index b341c36..50faa06 100644
--- a/cmake/external/nanopb.cmake
+++ b/cmake/external/nanopb.cmake
@@ -23,8 +23,6 @@ set(NANOPB_PROTOC_BIN ${FIREBASE_INSTALL_DIR}/bin/protoc)
 
 ExternalProject_Add(
   nanopb
-  DEPENDS
-    protobuf
 
   DOWNLOAD_DIR ${FIREBASE_DOWNLOAD_DIR}
   URL https://github.com/nanopb/nanopb/archive/nanopb-0.3.9.1.tar.gz
@@ -32,12 +30,8 @@ ExternalProject_Add(
 
   PREFIX ${PROJECT_BINARY_DIR}
 
-  CMAKE_ARGS
-    -DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}
-    -DCMAKE_INSTALL_PREFIX:STRING=${FIREBASE_INSTALL_DIR}
-    -DBUILD_SHARED_LIBS:BOOL=OFF
-    -Dnanopb_BUILD_GENERATOR:BOOL=ON
-    -Dnanopb_PROTOC_PATH:STRING=${NANOPB_PROTOC_BIN}
-
+  CONFIGURE_COMMAND ""
+  BUILD_COMMAND ""
+  INSTALL_COMMAND ""
   TEST_COMMAND ""
 )
diff --git a/cmake/utils.cmake b/cmake/utils.cmake
index 1c3cbd6..7d32624 100644
--- a/cmake/utils.cmake
+++ b/cmake/utils.cmake
@@ -89,3 +89,15 @@ function(add_objc_flags target)
     )
   endif()
 endfunction()
+
+# add_alias(alias_target actual_target)
+#
+# Adds a library alias target `alias_target` if it does not already exist,
+# aliasing to the given `actual_target` target. This allows library dependencies
+# to be specified uniformly in terms of the targets found in various
+# find_package modules even if the library is being built internally.
+function(add_alias ALIAS_TARGET ACTUAL_TARGET)
+  if(NOT TARGET ${ALIAS_TARGET})
+    add_library(${ALIAS_TARGET} ALIAS ${ACTUAL_TARGET})
+  endif()
+endfunction()