cmake: fix pylint/flake8 detection, update flake8 exclude

CMakeLists.txt

@@ -727,8 +727,15 @@ if(ENABLE_FLAKE8 AND PYTHON_DEFAULT_AVAILABLE)
     include("${CMAKE_CURRENT_LIST_DIR}/cmake/FindFlake8.cmake")
   endif()
   if(FLAKE8_FOUND)
+    list(APPEND OPENCV_FLAKE8_EXCLUDES ".git" "__pycache__" "config.py" "*.config.py" "config-*.py")
+    list(APPEND OPENCV_FLAKE8_EXCLUDES "svgfig.py")  # 3rdparty
+    if(NOT PYTHON3_VERSION_STRING VERSION_GREATER 3.6)
+      # Python 3.6+ (PEP 526): variable annotations (type hints)
+      list(APPEND OPENCV_FLAKE8_EXCLUDES "samples/dnn/dnn_model_runner/dnn_conversion/common/test/configs")
+    endif()
+    string(REPLACE ";" "," OPENCV_FLAKE8_EXCLUDES_STR "${OPENCV_FLAKE8_EXCLUDES}")
     add_custom_target(check_flake8
-        COMMAND "${FLAKE8_EXECUTABLE}" . --count --select=E9,E901,E999,F821,F822,F823 --show-source --statistics --exclude='.git,__pycache__,*.config.py,svgfig.py'
+        COMMAND "${FLAKE8_EXECUTABLE}" . --count --select=E9,E901,E999,F821,F822,F823 --show-source --statistics --exclude='${OPENCV_FLAKE8_EXCLUDES_STR}'
         WORKING_DIRECTORY "${OpenCV_SOURCE_DIR}"
         COMMENT "Running flake8"
     )

cmake/FindFlake8.cmake

@@ -12,9 +12,11 @@
 
 find_host_program(FLAKE8_EXECUTABLE flake8 PATHS /usr/bin)
 
-if(FLAKE8_EXECUTABLE)
+if(FLAKE8_EXECUTABLE AND NOT DEFINED FLAKE8_VERSION)
-  execute_process(COMMAND ${FLAKE8_EXECUTABLE} --version OUTPUT_VARIABLE FLAKE8_VERSION_RAW ERROR_QUIET)
+  execute_process(COMMAND ${FLAKE8_EXECUTABLE} --version RESULT_VARIABLE _result OUTPUT_VARIABLE FLAKE8_VERSION_RAW)
-  if(FLAKE8_VERSION_RAW MATCHES "^([0-9\\.]+[0-9])")
+  if(NOT _result EQUAL 0)
+    ocv_clear_vars(FLAKE8_EXECUTABLE FLAKE8_VERSION)
+  elseif(FLAKE8_VERSION_RAW MATCHES "^([0-9\\.]+[0-9])")
     set(FLAKE8_VERSION "${CMAKE_MATCH_1}")
   else()
     set(FLAKE8_VERSION "unknown")
@@ -22,6 +24,9 @@ if(FLAKE8_EXECUTABLE)
 endif()
 
 include(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(Flake8 DEFAULT_MSG FLAKE8_EXECUTABLE)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(Flake8
+    REQUIRED_VARS FLAKE8_EXECUTABLE
+    VERSION_VAR FLAKE8_VERSION
+)
 
 mark_as_advanced(FLAKE8_EXECUTABLE FLAKE8_VERSION)

cmake/FindPylint.cmake

@@ -12,9 +12,11 @@
 
 find_host_program(PYLINT_EXECUTABLE pylint PATHS /usr/bin)
 
-if(PYLINT_EXECUTABLE)
+if(PYLINT_EXECUTABLE AND NOT DEFINED PYLINT_VERSION)
-  execute_process(COMMAND ${PYLINT_EXECUTABLE} --version OUTPUT_VARIABLE PYLINT_VERSION_RAW ERROR_QUIET)
+  execute_process(COMMAND ${PYLINT_EXECUTABLE} --version RESULT_VARIABLE _result OUTPUT_VARIABLE PYLINT_VERSION_RAW)
-  if(PYLINT_VERSION_RAW MATCHES "pylint([^,]*) ([0-9\\.]+[0-9])")
+  if(NOT _result EQUAL 0)
+    ocv_clear_vars(PYLINT_EXECUTABLE PYLINT_VERSION)
+  elseif(PYLINT_VERSION_RAW MATCHES "pylint([^,]*) ([0-9\\.]+[0-9])")
     set(PYLINT_VERSION "${CMAKE_MATCH_2}")
   else()
     set(PYLINT_VERSION "unknown")
@@ -22,6 +24,9 @@ if(PYLINT_EXECUTABLE)
 endif()
 
 include(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(Pylint DEFAULT_MSG PYLINT_EXECUTABLE)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(Pylint
+    REQUIRED_VARS PYLINT_EXECUTABLE
+    VERSION_VAR PYLINT_VERSION
+)
 
 mark_as_advanced(PYLINT_EXECUTABLE PYLINT_VERSION)