Add flake8 linter ignore support

ament_cmake_flake8/cmake/ament_cmake_flake8_lint_hook.cmake

@@ -15,5 +15,6 @@
 file(GLOB_RECURSE _python_files FOLLOW_SYMLINKS "*.py")
 if(_python_files)
   message(STATUS "Added test 'flake8' to check Python code syntax and style conventions")
-  ament_flake8()
+  message(STATUS "Configured 'flake8' exclude dirs and/or files: ${AMENT_LINT_AUTO_FILE_EXCLUDE}")
+  ament_flake8(EXCLUDE ${AMENT_LINT_AUTO_FILE_EXCLUDE})
 endif()

ament_cmake_flake8/cmake/ament_flake8.cmake

@@ -31,13 +31,15 @@
 # :param MAX_LINE_LENGTH: override the maximum line length,
 #   the default is defined in ament_flake8
 # :type MAX_LINE_LENGTH: integer
+# :param EXCLUDE: an optional list of exclude directories or files for flake8
+# :type EXCLUDE: list
 # :param ARGN: the files or directories to check
 # :type ARGN: list of strings
 #
 # @public
 #
 function(ament_flake8)
-  cmake_parse_arguments(ARG "" "MAX_LINE_LENGTH;TESTNAME;CONFIG_FILE" "" ${ARGN})
+  cmake_parse_arguments(ARG "" "EXCLUDE;MAX_LINE_LENGTH;TESTNAME;CONFIG_FILE" "" ${ARGN})
   if(NOT ARG_TESTNAME)
     set(ARG_TESTNAME "flake8")
   endif()
@@ -57,7 +59,9 @@ function(ament_flake8)
   if(ARG_MAX_LINE_LENGTH)
     list(APPEND cmd "--linelength" "${ARG_MAX_LINE_LENGTH}")
   endif()
-  list(APPEND cmd ${ARG_UNPARSED_ARGUMENTS})
+  if(ARG_EXCLUDE)
+    list(APPEND cmd "--exclude" "${ARG_EXCLUDE}")
+  endif()
 
   file(MAKE_DIRECTORY "${CMAKE_BINARY_DIR}/ament_flake8")
   ament_add_test(

ament_lint_auto/doc/index.rst

@@ -47,7 +47,7 @@ in CMake ament packages.
 How to exclude files with ament_lint_auto?
 ------------------------------------------
 
-Linter hooks conform to the ament_lint_auto convention of excluding files
+Linter hooks shall conform to the ament_lint_auto convention of excluding files
 specified in the CMake list variable `AMENT_LINT_AUTO_FILE_EXCLUDE`.
 As such, the CMake snippet from above can be modified to exclude files across
 all linters with one addition.
@@ -62,3 +62,22 @@ all linters with one addition.
       set(AMENT_LINT_AUTO_FILE_EXCLUDE /path/to/ignored_file ...)
       ament_lint_auto_find_test_dependencies()
     endif()
+
+For a more specific example, this excludes all python files matching a pattern using globbing.
+Multiple expressions can be combined on multiple lines.
+It might be a good idea to issue a warning to developers that linting is disabled
+if you plan to enable it at some point.
+
+.. code:: cmake
+
+      file(GLOB_RECURSE AMENT_LINT_AUTO_FILE_EXCLUDE
+        # Exclude all the python files in src directory
+        src/*.py
+        # Exclude all the c++ implementation files in test directory
+        test/*.cpp
+      )
+      message(AUTHOR_WARNING
+          "Ament lint auto tests are disabled on the following: "
+          ${AMENT_LINT_AUTO_FILE_EXCLUDE}
+      )
+