build-aux: introduce 'black' tool for python formatting

The 'black' tool is intended to be an opinionated formatting
tool for python code. It is complementary to flake8 which
validates coding bad practices, but (mostly) ignores code
layout issues.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

build-aux/Makefile.in

@@ -3,6 +3,7 @@
 top_srcdir = @top_srcdir@
 top_builddir = @top_builddir@
 FLAKE8 = @flake8_path@
+BLACK = @black_path@
 RUNUTF8 = @runutf8@
 PYTHON = @PYTHON3@
 GREP = @GREP@

build-aux/meson.build

@@ -5,6 +5,10 @@ if git and tests_enabled[0]
   if flake8_prog.found()
     flake8_path = flake8_prog.full_path()
   endif
+  black_path = ''
+  if black_prog.found()
+    black_path = black_prog.full_path()
+  endif
 
   if host_machine.system() == 'freebsd' or host_machine.system() == 'darwin'
     make_prog = find_program('gmake')
@@ -35,6 +39,7 @@ if git and tests_enabled[0]
     'top_srcdir': meson.project_source_root(),
     'top_builddir': meson.project_build_root(),
     'flake8_path': flake8_path,
+    'black_path': black_path,
     'runutf8': ' '.join(runutf8),
     'PYTHON3': python3_prog.full_path(),
     'GREP': grep_prog.full_path(),

build-aux/syntax-check.mk

@@ -608,6 +608,16 @@ sc_flake8:
 		echo 'skipping test $@: flake8 not installed' 1>&2; \
 	fi
 
+sc_black:
+	if [ -n "$(BLACK)" ]; then \
+		DOT_PY=$$($(VC_LIST_EXCEPT) | $(GREP) '\.py$$'); \
+		BANG_PY=$$($(VC_LIST_EXCEPT) | xargs grep -l '^#!/usr/bin/env python3$$'); \
+		ALL_PY=$$(printf "%s\n%s" "$$DOT_PY" "$$BANG_PY" | sort -u); \
+		echo "$$ALL_PY" | xargs --no-run-if-empty $(BLACK) --check; \
+	else \
+		echo 'skipping test $@: black not installed' 1>&2; \
+	fi
+
 # mymain() in test files should use return, not exit, for nicer output
 sc_prohibit_exit_in_tests:
 	@prohibit='\<exit *\(' \
@@ -1307,6 +1317,11 @@ syntax-check: sc_spacing-check \
 		echo "* flake8 not installed, sc_flake8 has been skipped  *" >&2; \
 		echo "*****************************************************" >&2; \
 	fi
+	if [ -z "$(BLACK)" ]; then \
+		echo "*****************************************************" >&2; \
+		echo "* black not installed, sc_black has been skipped    *" >&2; \
+		echo "*****************************************************" >&2; \
+	fi
 endif
 
 # Don't include duplicate header in the source (either *.c or *.h)
@@ -1486,6 +1501,9 @@ exclude_file_name_regexp--sc_prohibit_select = \
   ^build-aux/syntax-check\.mk|src/util/vireventglibwatch\.c|tests/meson\.build$$
 
 
+exclude_file_name_regexp--sc_black = \
+  ^tools/|src/|tests/|ci/|run\.in|scripts/[^/]*\.py
+
 ## -------------- ##
 ## Implementation ##
 ## -------------- ##

meson.build

@@ -809,6 +809,7 @@ endforeach
 
 optional_programs = [
   'augparse',
+  'black',
   'dmidecode',
   'ebtables',
   'flake8',