Support building from extant generated source

Author: sethrj

CMakeLists.txt

@@ -13,35 +13,55 @@ enable_testing()
 # SWIG setup
 ##---------------------------------------------------------------------------##
 
-find_package(SWIG REQUIRED)
-list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
-include(CheckSWIGFortran)
-if (CMAKE_VERSION VERSION_LESS 3.20)
-  # TODO: This is until Fortran support gets added to the upstream cmake script
-  include(UseSWIGFortran)
+option(USE_SWIG "Enable SWIG generation" ON)
+if (USE_SWIG)
+  find_package(SWIG)
+endif()
+
+if (USE_SWIG AND SWIG_FOUND)
+  # SWIG is requested and available; make sure it's the Fortran fork.
+  list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
+  include(CheckSWIGFortran)
+  if (CMAKE_VERSION VERSION_LESS 3.20)
+    # TODO: This is until Fortran support gets added to the upstream cmake script
+    include(UseSWIGFortran)
+  else()
+    cmake_policy(SET CMP0078 "NEW")
+    cmake_policy(SET CMP0086 "NEW")
+    include(UseSWIG)
+  endif()
 else()
-  cmake_policy(SET CMP0078 "NEW")
-  cmake_policy(SET CMP0086 "NEW")
-  include(UseSWIG)
+  set(USE_SWIG FALSE)
 endif()
 
 ##---------------------------------------------------------------------------##
 # LIBRARY
 ##---------------------------------------------------------------------------##
+set(GENERATE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src/generated)
 
-macro(swig_fortran_add_library name)
+function(swig_fortran_add_library name)
   # We're using C++
   set_property(SOURCE src/${name}.i PROPERTY CPLUSPLUS ON)
   # We need to include the source directory
   set_property(SOURCE src/${name}.i
     PROPERTY USE_TARGET_INCLUDE_DIRECTORIES ON)
 
-  # Create the library
-  swig_add_library(${name}
-    LANGUAGE Fortran
-    TYPE USE_BUILD_SHARED_LIBS
-    OUTPUT_DIR ${CMAKE_CURRENT_SOURCE_DIR}/src/generated
-    SOURCES src/${name}.i ${ARGN})
+  if (USE_SWIG)
+    # SWIG is available; actually generate the library dynamically.
+    # Create the library
+    swig_add_library(${name}
+      LANGUAGE Fortran
+      TYPE USE_BUILD_SHARED_LIBS
+      OUTPUT_DIR "${GENERATE_DIR}"
+      SOURCES src/${name}.i ${ARGN})
+  else()
+    # SWIG is *not* being used: compile the code committed in the repository,
+    # generated by the developer with SWIG.
+    add_library(${name}
+      "${GENERATE_DIR}/${name}.f90"
+      "${GENERATE_DIR}/${name}FORTRAN_wrap.cxx"
+      ${ARGN})
+  endif()
 
   # Enable C++11
   target_compile_features(${name} PRIVATE cxx_std_11)
@@ -61,7 +81,7 @@ macro(swig_fortran_add_library name)
           $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}>
           $<INSTALL_INTERFACE:modules>
   )
-endmacro()
+endfunction()
 
 # Four SWIG libraries
 swig_fortran_add_library(utils)