add code styling mandatory

.travis.yml

@@ -1,7 +1,7 @@
 language: cpp
 dist: bionic
 before_install:
-  - sudo apt-get install -y cmake g++ make libqt5webkit5-dev libqt5svg5-dev qtbase5-dev qttools5-dev qttools5-dev-tools libasound2-dev
+  - sudo apt-get install -y cmake g++ make libqt5webkit5-dev libqt5svg5-dev qtbase5-dev qttools5-dev qttools5-dev-tools libasound2-dev clang-format
 script:
   - pwd && source ./travis-build.sh
 

travis-build.sh

@@ -1,8 +1,24 @@
-#!/bin/sh
-cd ..
-mkdir -p build
-cd build
+#!/bin/bash
+# This script is run from the CI service and does:
+# 1) checks, if code is correctly formatted.
+# 2) compiles canorus
+# 3) installs canorus locally
+
+set -euxo pipefail
+
+mkdir -p ../build
+cd ../build
 cmake -D CMAKE_INSTALL_PREFIX=~/.local ../canorus
+
+echo "Check, if code is formatted with \"make fmt\"..."
+make fmt
+cd ../canorus
+# Output diff, if any.
+git diff
+# Abort, if there are any differences.
+git diff --quiet
+cd ../build
+
 make -j4 
 make tr
 make install