ARROW-4363: [CI] [C++] Add CMake format checks

- Add a top-level script that reformats all known CMake files in the source tree
- Add a lint step in Travis that checks CMake files are properly formatted

Requires [cmake_format](https://github.com/cheshirekow/cmake_format) and Python 3.

Author: Antoine Pitrou <antoine@python.org>

Closes #3606 from pitrou/ARROW-4363-cmake-format and squashes the following commits:

762df29 <Antoine Pitrou> Add mention in cpp/README.md
9073af9 <Antoine Pitrou> ARROW-4363:   Add CMake format checks

Author: pitrou

.travis.yml

@@ -50,8 +50,6 @@ matrix:
     os: linux
     language: python
     python: "3.6"
-    env:
-    - ARROW_TRAVIS_CLANG_FORMAT=1
     before_script:
     # Always run RAT checks, in case another build in matrix breaks RAT
     - $TRAVIS_BUILD_DIR/ci/travis_release_audit.sh

ci/travis_lint.sh

@@ -23,17 +23,18 @@ set -ex
 export ARROW_TRAVIS_USE_TOOLCHAIN=0
 source $TRAVIS_BUILD_DIR/ci/travis_env_common.sh
 
+# CMake formatting check
+pip install cmake_format
+$TRAVIS_BUILD_DIR/run-cmake-format.py --check
+
 # C++ code linting
 if [ "$ARROW_CI_CPP_AFFECTED" != "0" ]; then
   mkdir $ARROW_CPP_DIR/lint
   pushd $ARROW_CPP_DIR/lint
 
   cmake .. -DARROW_ONLY_LINT=ON
   make lint
-
-  if [ "$ARROW_TRAVIS_CLANG_FORMAT" == "1" ]; then
-    make check-format
-  fi
+  make check-format
 
   python $ARROW_CPP_DIR/build-support/lint_cpp_cli.py $ARROW_CPP_DIR/src
 

cmake-format.py

@@ -0,0 +1,59 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# cmake-format configuration file
+# Use run-cmake-format.py to reformat all cmake files in the source tree
+
+# How wide to allow formatted cmake files
+line_width = 90
+
+# How many spaces to tab for indent
+tab_size = 2
+
+# If arglists are longer than this, break them always
+max_subargs_per_line = 4
+
+# If true, separate flow control names from their parentheses with a space
+separate_ctrl_name_with_space = False
+
+# If true, separate function names from parentheses with a space
+separate_fn_name_with_space = False
+
+# If a statement is wrapped to more than one line, than dangle the closing
+# parenthesis on it's own line
+dangle_parens = False
+
+# What style line endings to use in the output.
+line_ending = 'unix'
+
+# Format command names consistently as 'lower' or 'upper' case
+command_case = 'lower'
+
+# Format keywords consistently as 'lower' or 'upper' case
+keyword_case = 'unchanged'
+
+# enable comment markup parsing and reflow
+enable_markup = False
+
+# If comment markup is enabled, don't reflow the first comment block in
+# eachlistfile. Use this to preserve formatting of your
+# copyright/licensestatements.
+first_comment_is_literal = False
+
+# If comment markup is enabled, don't reflow any comment block which matchesthis
+# (regex) pattern. Default is `None` (disabled).
+literal_comment_pattern = None