Add black wrapper

Some system roles want not to run black on their code. This wrapper
decides whether to run black or not depending on content of config.sh.
This wrapper also allows to set patterns of files and directories via
config.sh to be processed or skipped by black.

.travis/config.sh

@@ -7,5 +7,14 @@
 #
 #       - LSR_EXTRA_PACKAGES
 #
+# Environment variables that not start with LSR_* but have influence on CI
+# process:
+#
+#   * .travis/runblack.sh:
+#
+#       - RUN_BLACK_INCLUDE
+#       - RUN_BLACK_EXCLUDE
+#       - RUN_BLACK_DISABLED
+#
 
 export LSR_MOLECULE_DEPS='-rmolecule_requirements.txt'

.travis/runblack.sh

@@ -0,0 +1,70 @@
+#!/bin/bash
+# SPDX-License-Identifier: MIT
+
+# A shell wrapper around black (Python formatter). The purpose of this wrapper
+# is to get a user the opportunity to control black from config.sh via setting
+# environment variables.
+
+# The first script argument is a path to Python interpreter, the rest of
+# arguments are passed to black.
+
+# Environment variables:
+#
+#   RUN_BLACK_INCLUDE
+#     a regular expression specifying files to be included; can be overridden
+#     from command line by --include;
+#
+#   RUN_BLACK_EXCLUDE
+#     a regular expression specifying files to be excluded; can be overridden
+#     from command line by --exclude;
+#
+#   RUN_BLACK_DISABLED
+#     if set to an arbitrary non-empty value, black will be not executed
+
+set -e
+
+ME=$(basename $0)
+SCRIPTDIR=$(readlink -f $(dirname $0))
+
+. ${SCRIPTDIR}/utils.sh
+. ${SCRIPTDIR}/config.sh
+
+if [[ "${RUN_BLACK_DISABLED}" ]]; then
+  lsr_info "${ME}: black is disabled. Skipping."
+  exit 0
+fi
+
+# Sanitize path in case if running within tox (see
+# https://github.com/tox-dev/tox/issues/1463):
+ENVPYTHON=$(readlink -f $1)
+shift
+
+DEFAULT_INCLUDE='^[^.].*\.py$'
+DEFAULT_EXCLUDE='/(\.[^.].*|tests/roles)/'
+
+INCLUDE_ARG=""
+EXCLUDE_ARG=""
+OTHER_ARGS=()
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --include)
+      shift
+      INCLUDE_ARG="$1"
+      ;;
+    --exclude)
+      shift
+      EXCLUDE_ARG="$1"
+      ;;
+    *)
+      OTHER_ARGS+=( "$1" )
+      ;;
+  esac
+  shift
+done
+
+set -x
+${ENVPYTHON} -m black \
+  --include "${INCLUDE_ARG:-${RUN_BLACK_INCLUDE:-${DEFAULT_INCLUDE}}}" \
+  --exclude "${EXCLUDE_ARG:-${RUN_BLACK_EXCLUDE:-${DEFAULT_EXCLUDE}}}" \
+  "${OTHER_ARGS[@]}"

tox.ini

@@ -126,10 +126,13 @@ commands =
 [testenv:black]
 envdir = {toxworkdir}/env-{env:TRAVIS_PYTHON_VERSION:3.6}
 basepython = python3.6
+passenv = RUN_BLACK_*
 deps =
     black
+whitelist_externals =
+    {[base]whitelist_externals}
 commands =
-    black --check --diff --include "^[^.].*\.py$" --exclude "/(\.[^.].*|tests/roles)/" .
+    bash {toxinidir}/.travis/runblack.sh {envpython} --check --diff .
 
 [testenv:pylint]
 envdir = {toxworkdir}/env-{env:TRAVIS_PYTHON_VERSION:2.7}