Adding option to automatically installation

This extends FindPystencilsSfG.cmake with a Cache Variable CODEGEN_PRIVATE_VENV. This is set by default and if activate it creates a python venv and installs either dependencies from a requirements.txt or if this is not present it downloads the latest pystenicls-sfg/pystencils versions. If a custom Interpreter is passed to cmake this deactivated.

In external CMake Projects this files could by included via

## Pystencils-sfg setups
set(FIND_PYSTENCILSSFG_CMAKE_PATH "${CMAKE_BINARY_DIR}/_pystencilssfg-cmake/")
file(DOWNLOAD
    "https://i10git.cs.fau.de/ob28imeq/pystencils-sfg/-/raw/cmake_setup/src/pystencilssfg/cmake/FindPystencilsSfg.cmake?ref_type=heads"
    "${FIND_PYSTENCILSSFG_CMAKE_PATH}/FindPystencilsSfg.cmake"
)

SET ( CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${FIND_PYSTENCILSSFG_CMAKE_PATH})

find_package( PystencilsSfg REQUIRED )

src/pystencilssfg/cmake/FindPystencilsSfg.cmake

@@ -27,7 +27,7 @@ if(NOT DEFINED CACHE{PystencilsSfg_PYTHON_INTERPRETER})
         set( _sfg_cache_python_init ${PystencilsSfg_PYTHON_PATH} )
 
     elseif (CODEGEN_PRIVATE_VENV)
-        #   ... or create own venv ...
+        #   ... or create an own venv ...
 
         set(CODEGEN_VENV_PATH ${CMAKE_CURRENT_BINARY_DIR}/codegen-venv CACHE PATH "Location of the virtual environment used for code generation")
         set(_venv_python_exe ${CODEGEN_VENV_PATH}/bin/python)
@@ -44,14 +44,26 @@ if(NOT DEFINED CACHE{PystencilsSfg_PYTHON_INTERPRETER})
                 )
             endif()
 
-            message( STATUS "Installing required Python packages..." )
 
-            set(CODEGEN_VENV_REQUIREMENTS ${PROJECT_SOURCE_DIR}/requirements.txt CACHE PATH "Location of the requirements installed in the virtual environment used for code generation")
-            execute_process(
-            COMMAND ${_venv_python_exe} -m pip install -r ${CODEGEN_VENV_REQUIREMENTS}
-            OUTPUT_QUIET
-            )
-            #TODO automatically install pystencilssfg/pystencils
+            set(CODEGEN_VENV_REQUIREMENTS ${PROJECT_SOURCE_DIR}/requirements.txt CACHE FILEPATH "Location of the requirements installed in the virtual environment used for code generation")
+            if (EXISTS ${CODEGEN_VENV_REQUIREMENTS})
+                message( STATUS "Installing required Python packages from ${CODEGEN_VENV_REQUIREMENTS}" )
+                execute_process( COMMAND ${_venv_python_exe} -m pip install -r ${CODEGEN_VENV_REQUIREMENTS} OUTPUT_QUIET)
+            else()
+                set(Pystencils_URL "git+https://i10git.cs.fau.de/pycodegen/pystencils.git@v2.0-dev" CACHE STRING "Location of pystencils to installed in the virtual environment used for code generation")
+                set(PystencilsSfg_URL "git+https://i10git.cs.fau.de/pycodegen/pystencils-sfg.git" CACHE STRING "Location of pystencils-sfg to installed in the virtual environment used for code generation")
+
+                message( STATUS "Installing required Pystencils from ${Pystencils_URL}" )
+                execute_process(
+                    COMMAND ${_venv_python_exe} -m pip install "${Pystencils_URL}"
+                    OUTPUT_QUIET
+                )
+                message( STATUS "Installing required Pystencils-sfg from ${PystencilsSfg_URL}" )
+                execute_process(
+                    COMMAND ${_venv_python_exe} -m pip install "${PystencilsSfg_URL}"
+                    OUTPUT_QUIET
+                )
+            endif()
 
             set( _sfg_private_venv_done TRUE CACHE BOOL "" )
             mark_as_advanced(_sfg_private_venv_done)