ci: check examples code style

Use code style defined in Arduino project to check code style of the
examples. The check is done by formatting all files with astyle and
checking whether any changes have been introduced.

.travis.yml

@@ -3,6 +3,10 @@ language: bash
 os: linux
 dist: trusty
 
+cache:
+  directories:
+    - $HOME/astyle
+
 matrix:
   include:
     - env:
@@ -15,9 +19,23 @@ matrix:
       - BUILD_TYPE=package
     - env:
       - BUILD_TYPE=host_tests
+    - env:
+      - BUILD_TYPE=style_check
 
 install:
-  - pip install --user -r doc/requirements.txt
+  - >
+      [ "$BUILD_TYPE" = "docs" ] && {
+        pip install --user -r doc/requirements.txt;
+      } || true
+  - >
+      [ "$BUILD_TYPE" = "style_check" ] && {
+        [ -f $HOME/astyle/build/gcc/bin/astyle ] || {
+          wget -O astyle_3.1_linux.tar.gz https://sourceforge.net/projects/astyle/files/astyle/astyle%203.1/astyle_3.1_linux.tar.gz/download;
+          tar -xf astyle_3.1_linux.tar.gz -C $HOME;
+          make -C $HOME/astyle/build/gcc;
+        }
+        make -C $HOME/astyle/build/gcc prefix=$HOME install;
+      } || true
 
 script:
   - $TRAVIS_BUILD_DIR/tests/common.sh

tests/common.sh

@@ -213,8 +213,30 @@ function build_sketches_with_arduino()
     echo -e "travis_fold:end:size_report"
 }
 
+function check_examples_style()
+{
+    echo -e "travis_fold:start:check_examples_style"
+
+    find $TRAVIS_BUILD_DIR/libraries -name '*.ino' -exec \
+        astyle \
+            --suffix=none \
+            --options=$TRAVIS_BUILD_DIR/tests/examples_style.conf {} \;
+
+    git diff --exit-code -- $TRAVIS_BUILD_DIR/libraries
+
+    echo -e "travis_fold:end:check_examples_style"
+}
+
 set -e
 
+if [ -z "$TRAVIS_BUILD_DIR" ]; then
+    echo "TRAVIS_BUILD_DIR is not set, trying to guess:"
+    pushd $(dirname $0)/../ > /dev/null
+    TRAVIS_BUILD_DIR=$PWD
+    popd > /dev/null
+    echo "TRAVIS_BUILD_DIR=$TRAVIS_BUILD_DIR"
+fi
+
 if [ "$BUILD_TYPE" = "build" ]; then
     install_arduino
     build_sketches_with_arduino
@@ -236,5 +258,11 @@ elif [ "$BUILD_TYPE" = "host_tests" ]; then
     # Run host side tests
     cd $TRAVIS_BUILD_DIR/tests
     run_host_tests
+elif [ "$BUILD_TYPE" = "style_check" ]; then
+    # Check code style
+    check_examples_style
+else
+    echo "BUILD_TYPE not set"
+    exit 1
 fi
 

tests/examples_style.conf

@@ -0,0 +1,44 @@
+# Code formatting rules for Arduino examples, taken from:
+#
+#   https://github.com/arduino/Arduino/blob/master/build/shared/examples_formatter.conf
+#
+
+mode=c
+lineend=linux
+
+# 2 spaces indentation
+indent=spaces=2
+
+# also indent macros
+indent-preprocessor
+
+# indent classes, switches (and cases), comments starting at column 1
+indent-classes
+indent-switches
+indent-cases
+indent-col1-comments
+
+# put a space around operators
+pad-oper
+
+# put a space after if/for/while
+pad-header
+
+# if you like one-liners, keep them
+keep-one-line-statements
+add-braces
+
+style=java
+attach-namespaces
+attach-classes
+attach-inlines
+attach-extern-c
+indent-modifiers
+indent-namespaces
+indent-labels
+indent-preproc-block
+indent-preproc-define
+indent-preproc-cond
+unpad-paren
+add-braces
+remove-comment-prefix