Check code formatting compliance during the CI build

Use the Artistic Style formatting tool (also used for the Arduino IDE's auto format feature) to check all code files in the repository for compliance with the Arduino code formatting style.

Author: per1234

.travis.yml

@@ -28,6 +28,26 @@ matrix:
       install:
         - arduino-cli core install arduino:sam
 
+    # check all code files for compliance with the Arduino code formatting style
+    - env:
+        - NAME='Code Formatting Check'
+      language: minimal
+      before_install:
+        # install Artistic Style code formatter tool: http://astyle.sourceforge.net
+        - |
+          mkdir "${HOME}/astyle";
+          wget --no-verbose --output-document="${HOME}/astyle/astyle.tar.gz" "https://iweb.dl.sourceforge.net/project/astyle/astyle/astyle%203.1/astyle_3.1_linux.tar.gz";
+          tar --extract --file="${HOME}/astyle/astyle.tar.gz" --directory="${HOME}/astyle";
+          cd "${HOME}/astyle/astyle/build/gcc";
+          make;
+          export PATH="$PWD/bin:$PATH";
+          cd "$TRAVIS_BUILD_DIR"
+        # download Arduino's Artistic Style configuration file
+        - wget --directory-prefix="${HOME}/astyle" https://raw.githubusercontent.com/arduino/Arduino/master/build/shared/examples_formatter.conf
+      script:
+        # check code formatting
+        - find . -regextype posix-extended -path './.git' -prune -or \( -iregex '.*\.((ino)|(h)|(hpp)|(hh)|(hxx)|(h\+\+)|(cpp)|(cc)|(cxx)|(c\+\+)|(cp)|(c)|(ipp)|(ii)|(ixx)|(inl)|(tpp)|(txx)|(tpl))$' -and -type f \) -print0 | xargs -0 -L1 bash -c 'if ! diff "$0" <(astyle --options=${HOME}/astyle/examples_formatter.conf --dry-run < "$0"); then echo "Non-compliant code formatting in $0"; false; fi'
+
 # default phases shared by the compilation tests
 before_install:
   - wget http://downloads.arduino.cc/arduino-cli/arduino-cli-$CLI_VERSION-linux64.tar.bz2