make, scripts: Add support for static Python typechecking

This commit adds support for static typechecking with mypy.

Notable additions:

  - A new target "check" which does the type checking

  - Py-mods.mk, meant to be included from a directory containing python modules
    in subdirectories, but not being a python module itself. It makes the all
    target depend on check only if PY_RUN_CHECK_AFTER_BUILD is defined and
    true.  That's because pypy is under heavy development, and the Ubuntu 18.04
    version is too old to work for lots of the code.

Signed-off-by: Jan Lindemann <jan@janware.com>

make/py-defs.mk

@@ -21,6 +21,8 @@ ifndef PY_PREREQ_BUILD_DIRS
   PY_PREREQ_BUILD_DIRS      := $(shell $(proj_query_cmd) proj-dir $(PY_PREREQ_BUILD))
 endif
 
+PY_MYPY                     ?= mypy --ignore-missing-imports
+
 PY_SRC_PY                   ?= $(wildcard *.py)
 PY_ALL_PY                    = $(PY_SRC_PY)
 
@@ -66,7 +68,8 @@ PY_INSTALLED_REG             = $(PY_INSTALLED_PY) $(PY_INSTALLED_PYC)
 
 PYTHONPATH                  ?= $(call proj_query, pythonpath $(PROJECT) $(PY_PREREQ_RUN))
 #PYTHONPATH                  = $(subst $(space),,$(ENV_PYTHONPATH)$(foreach d,$(PY_MODULE_DIRS),:$(d)))
-export PYTHONPATH
+MYPYPATH                     = $(PYTHONPATH)
+export PYTHONPATH MYPYPATH
 
 # not used anywhere
 #PY_PROJ_MODULE_DIRS        ?= $(wildcard $(foreach subdir,/tools/python /src/python,$(addsuffix $(subdir),$(TOPDIR) $(PY_PREREQ_BUILD_DIRS))))
@@ -84,6 +87,7 @@ echo-py:
 	@echo "PY_SITE_PACKAGES_PATH   = $(PY_SITE_PACKAGES_PATH)"
 	@echo "PY_MODULES              = $(PY_MODULES)"
 	@echo "PYTHONPATH              = $(PYTHONPATH)"
+	@echo "MYPYPATH                = $(MYPYPATH)"
 	@echo "PY_INSTALL_MOD          = $(PY_INSTALL_MOD)"
 	@echo "PY_INSTALL_SUB_MOD      = $(PY_INSTALL_SUB_MOD)"
 	# not used anywhere"