* Fix flake8 whitespace reports
$ flake8 | grep -E '(E203|E221|E226|E303|W291|W293)'
./mesonbuild/coredata.py:337:5: E303 too many blank lines (2)
* Fix flake8 'variable assigned value but unused' reports
$ flake8 | grep -E F841
./mesonbuild/modules/gnome.py:922:9: F841 local variable 'target_name' is assigned to but never used
* Fix flake8 'imported but unused' reports
$ flake8 | grep F401
./mesonbuild/compilers/__init__.py:128:1: F401 '.c.ArmclangCCompiler' imported but unused
./mesonbuild/compilers/__init__.py:138:1: F401 '.cpp.ArmclangCPPCompiler' imported but unused
./mesonbuild/modules/__init__.py:4:1: F401 '..mlog' imported but unused
PR #3717 imports ARMCLANG compilers in __init__, but does not add them to
__all__, so they are not re-exported by the compilers package like
everything else.
* More details about flake8 in Contributing.md
Mention that Sider runs flake8
Suggest seting flake8 as a pre-commit hook
Jon Turney