Add FIREBASE_PYTHON_EXECUTABLE cmake cache var

Author: dconeybe

CMakeLists.txt

@@ -72,6 +72,21 @@ option(
   ON
 )
 
+# Find a Python interpreter using the best available mechanism.
+if(${CMAKE_VERSION} VERSION_LESS "3.12")
+  include(FindPythonInterp)
+  set(DEFAULT_FIREBASE_PYTHON_EXECUTABLE "${PYTHON_EXECUTABLE}")
+else()
+  find_package(Python3 COMPONENTS Interpreter)
+  set(DEFAULT_FIREBASE_PYTHON_EXECUTABLE "${Python3_EXECUTABLE}")
+endif()
+
+set(
+  FIREBASE_PYTHON_EXECUTABLE
+  "${DEFAULT_FIREBASE_PYTHON_EXECUTABLE}"
+  CACHE FILEPATH
+  "The Python interpreter to use"
+)
 
 list(INSERT CMAKE_MODULE_PATH 0 ${PROJECT_SOURCE_DIR}/cmake)
 include(compiler_setup)

Firestore/Protos/CMakeLists.txt

@@ -12,8 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-include(FindPythonInterp)
-
 # Generate output in-place. So long as the build is idempotent this helps
 # verify that the protoc-generated output isn't changing.
 set(OUTPUT_DIR ${CMAKE_CURRENT_SOURCE_DIR})
@@ -200,7 +198,7 @@ if(FIREBASE_IOS_PROTOC_GENERATE_SOURCES)
     COMMENT "Generating nanopb sources"
     OUTPUT ${NANOPB_GENERATED_SOURCES}
     COMMAND
-      ${PYTHON_EXECUTABLE}
+      ${FIREBASE_PYTHON_EXECUTABLE}
         ${CMAKE_CURRENT_SOURCE_DIR}/build_protos.py
         --nanopb
         --protoc=$<TARGET_FILE:protoc>
@@ -232,7 +230,7 @@ if(FIREBASE_IOS_PROTOC_GENERATE_SOURCES)
     COMMENT "Generating C++ protobuf sources"
     OUTPUT ${PROTOBUF_CPP_GENERATED_SOURCES}
     COMMAND
-      ${PYTHON_EXECUTABLE}
+      ${FIREBASE_PYTHON_EXECUTABLE}
         ${CMAKE_CURRENT_SOURCE_DIR}/build_protos.py
         --cpp
         --protoc=$<TARGET_FILE:protoc>

Firestore/core/CMakeLists.txt

@@ -14,7 +14,6 @@
 
 include(CheckSymbolExists)
 include(CheckIncludeFiles)
-include(FindPythonInterp)
 
 
 ## firestore_util
@@ -286,7 +285,7 @@ add_custom_command(
   OUTPUT
   ${GRPC_ROOT_CERTIFICATE_SOURCES}
   COMMAND
-  ${PYTHON_EXECUTABLE} ${FIREBASE_SOURCE_DIR}/scripts/binary_to_array.py
+  ${FIREBASE_PYTHON_EXECUTABLE} ${FIREBASE_SOURCE_DIR}/scripts/binary_to_array.py
   --output_header=${OUTPUT_DIR}/grpc_root_certificates_generated.h
   --output_source=${OUTPUT_DIR}/grpc_root_certificates_generated.cc
   --cpp_namespace=firebase::firestore::remote