From 82e164949bfd6416b5beae2dcd8a502954d4bcf7 Mon Sep 17 00:00:00 2001
From: Christian Blichmann <cblichmann@google.com>
Date: Fri, 17 Jun 2022 05:55:49 -0700
Subject: [PATCH] CMake: Move proto import path replacement to build time

With this change, the generated build system can now decide when the SAPI
protos are out of date and need to be rebuilt. Previously, the protos had
to always be regenerated which meant compiling a big part of the codebase
after each CMake configure run, even if nothing else changed.

PiperOrigin-RevId: 455599389
Change-Id: If75b6e870cd37f3136681fc73a404c5678623e52
---
 cmake/SapiUtil.cmake | 37 +++++++++++++++++++++++++------------
 1 file changed, 25 insertions(+), 12 deletions(-)

diff --git a/cmake/SapiUtil.cmake b/cmake/SapiUtil.cmake
index 2e6b11e..1601ba0 100644
--- a/cmake/SapiUtil.cmake
+++ b/cmake/SapiUtil.cmake
@@ -46,12 +46,25 @@ function(sapi_protobuf_generate_cpp SRCS HDRS)
   endif()
 
   foreach(_file IN LISTS _pb_UNPARSED_ARGUMENTS)
-    file(READ "${_file}" _pb_orig)
-    string(REGEX REPLACE "import \".*/([^/]+\\.proto)\""
-                         "import \"\\1\"" _pb_repl "${_pb_orig}")
-    set(_file "${CMAKE_CURRENT_BINARY_DIR}/${_file}")
-    file(WRITE "${_file}" "${_pb_repl}")
-    list(APPEND _pb_files "${_file}")
+    get_filename_component(_abs_file_orig "${_file}" ABSOLUTE)
+    get_filename_component(_abs_file_repl
+                           "${CMAKE_CURRENT_BINARY_DIR}/${_file}" ABSOLUTE)
+
+    # Add a CMake script that replaces the actual import paths. An extra
+    # script file is necessary so that this happens at build time.
+    set(_cmake_gen "${CMAKE_CURRENT_BINARY_DIR}/${_file}.gen.cmake")
+    file(WRITE "${_cmake_gen}" "\
+file(READ \"${_abs_file_orig}\" _pb_orig)
+string(REGEX REPLACE \"import \\\".*/([^/]+\\\\.proto)\\\"\"\
+                     \"import \\\"\\\\1\\\"\" _pb_repl \"\${_pb_orig}\")
+file(WRITE \"${_abs_file_repl}\" \"\${_pb_repl}\")\
+")
+    add_custom_command(OUTPUT "${_abs_file_repl}"
+                       COMMAND "${CMAKE_COMMAND}"
+                       ARGS -P "${_cmake_gen}"
+                       DEPENDS "${_abs_file_orig}")
+
+    list(APPEND _pb_files "${_abs_file_repl}")
   endforeach()
 
   set(_outvar)
@@ -140,8 +153,8 @@ function(sapi_protobuf_generate)
 
   # Create an include path for each file specified
   foreach(_file ${_pb_PROTOS})
-    get_filename_component(_abs_file ${_file} ABSOLUTE)
-    get_filename_component(_abs_path ${_abs_file} PATH)
+    get_filename_component(_abs_file "${_file}" ABSOLUTE)
+    get_filename_component(_abs_path "${_abs_file}" PATH)
     list(FIND _protobuf_include_path "${_abs_path}" _contains_already)
     if(${_contains_already} EQUAL -1)
       list(APPEND _protobuf_include_path -I ${_abs_path})
@@ -158,9 +171,9 @@ function(sapi_protobuf_generate)
 
   set(_generated_srcs_all)
   foreach(_proto IN LISTS _pb_PROTOS)
-    get_filename_component(_abs_file ${_proto} ABSOLUTE)
-    get_filename_component(_abs_dir ${_abs_file} DIRECTORY)
-    get_filename_component(_basename ${_proto} NAME_WE)
+    get_filename_component(_abs_file "${_proto}" ABSOLUTE)
+    get_filename_component(_abs_dir "${_abs_file}" DIRECTORY)
+    get_filename_component(_basename "${_proto}" NAME_WE)
 
     set(_generated_srcs)
     foreach(_ext ${_pb_GENERATE_EXTENSIONS})
@@ -170,7 +183,7 @@ function(sapi_protobuf_generate)
     list(APPEND _generated_srcs_all ${_generated_srcs})
 
     add_custom_command(OUTPUT ${_generated_srcs}
-                       COMMAND  protobuf::protoc
+                       COMMAND protobuf::protoc
                        ARGS --${_pb_LANGUAGE}_out
                             ${_dll_export_decl}${_pb_PROTOC_OUT_DIR}
                             ${_protobuf_include_path}