build: change flake8 to use blacklist instead of whitelist

The current flake8 check only looks at one item (semicolons at end of
line). This means that our code quality will continue to get worse,
violating an increasing number of checks.

Switching to a whitelist means that we freeze the badness at its
current level & can incrementally fix things up.

We are excluding the following...

Indentation:

  E114 indentation is not a multiple of four (comment)
  E115 expected an indented block (comment)
  E116 unexpected indentation (comment)
  E121 continuation line under-indented for hanging indent
  E125 continuation line with same indent as next logical line
  E126 continuation line over-indented for hanging indent
  E127 continuation line over-indented for visual indent
  E128 continuation line under-indented for visual indent
  E129 visually indented line with same indent as next logical line
  E131 continuation line unaligned for hanging indent

Whitespace:

  E211 whitespace before ‘(‘
  E221 multiple spaces before operator
  E222 multiple spaces after operator
  E225 missing whitespace around operator
  E226 missing whitespace around arithmetic operator
  E231 missing whitespace after ‘,’, ‘;’, or ‘:’
  E261 at least two spaces before inline comment

Blank lines

  E301 expected 1 blank line, found 0
  E302 expected 2 blank lines, found 0
  E303 too many blank lines (3)
  E305 expected 2 blank lines after end of function or class

Line length

  E501 line too long (82 > 79 characters)

Statements

  E722 do not use bare except, specify exception instead
  E741 do not use variables named ‘l’, ‘O’, or ‘I’

Errors:

  F821 undefined name 'name'

Warnings:

  W504 line break after binary operator
  W605 invalid escape sequence ‘x’

Later commits will enable most of these exclusions.
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

build-aux/syntax-check.mk

@@ -882,11 +882,28 @@ sc_require_enum_last_marker:
 	  { echo '$(ME): enum impl needs _LAST marker on second line' 1>&2; \
 	    exit 1; } || :
 
-# In Python files we don't want to end lines with a semicolon like in C
+# Validate many python style rules
+FLAKE8_INDENTATION = E114,E115,E116,E121,E125,E126,E127,E128,E129,E131
+FLAKE8_WHITESPACE = E211,E221,E222,E225,E226,E231,E261
+FLAKE8_BLANK_LINES = E301,E302,E303,E305
+FLAKE8_LINE_LENGTH = E501
+FLAKE8_STATEMENTS = E722,E741
+FLAKE8_ERRORS = F821
+FLAKE8_WARNINGS = W504,W605
+
+FLAKE8_IGNORE = $(FLAKE8_INDENTATION),$\
+		$(FLAKE8_WHITESPACE),$\
+		$(FLAKE8_BLANK_LINES),$\
+		$(FLAKE8_LINE_LENGTH),$\
+		$(FLAKE8_STATEMENTS),$\
+		$(FLAKE8_ERRORS),$\
+		$(FLAKE8_WARNINGS) \
+		$(NULL)
+
 sc_flake8:
 	@if [ -n "$(FLAKE8)" ]; then \
 		$(VC_LIST_EXCEPT) | $(GREP) '\.py$$' | xargs \
-			$(FLAKE8) --select E703 --show-source; \
+			$(FLAKE8) --ignore $(FLAKE8_IGNORE) --show-source; \
 	else \
 		echo '$(ME): skipping test $@: flake8 not installed' 1>&2; \
 	fi