Travis: Run clang-format static check

Commits or PRs that do not respect the clang-format style that we
enforce will fail the test.

Adding ubuntu-toolchain-r-test as its libstdc++ is necessary to install
libllvm-3.9.

(cherry picked from commit 6aee289b3e)

.travis.yml

@@ -18,6 +18,8 @@ env:
   - GODOT_TARGET=windows
 
 matrix:
+  include:
+    - env: STATIC_CHECKS=yes
   exclude:
     - os: linux
       env: GODOT_TARGET=iphone
@@ -42,6 +44,9 @@ matrix:
 
 addons:
   apt:
+    sources:
+      - ubuntu-toolchain-r-test
+      - llvm-toolchain-trusty-3.9
     packages:
       - build-essential
       - scons
@@ -65,6 +70,9 @@ addons:
       - g++-mingw-w64-x86-64
       - mingw-w64
 
+      # For style checks.
+      - clang-format-3.9
+
 
 before_script:
   - if [ "$TRAVIS_OS_NAME" = "osx" ]; then brew update; brew install scons; fi
@@ -75,4 +83,8 @@ before_script:
     fi
 
 script:
-  - scons platform=$GODOT_TARGET CXX=$CXX openssl=builtin
+  - if [ "$STATIC_CHECKS" = "yes" ]; then
+      sh ./misc/travis/clang-format.sh;
+    else
+      scons platform=$GODOT_TARGET CXX=$CXX openssl=builtin;
+    fi

misc/travis/clang-format.sh

@@ -0,0 +1,40 @@
+#!/bin/sh
+
+CLANG_FORMAT=clang-format-3.9
+
+if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
+    # Check the whole commit range against $TRAVIS_BRANCH, the base merge branch
+    # We could use $TRAVIS_COMMIT_RANGE but it doesn't play well with force pushes
+    RANGE="$(git rev-parse $TRAVIS_BRANCH) HEAD"
+else
+    # Test only the last commit
+    RANGE=HEAD
+fi
+
+FILES=$(git diff-tree --no-commit-id --name-only -r $RANGE | grep -v thirdparty/ | grep -e "\.cpp$" -e "\.h$" -e "\.inc$")
+echo "Checking files:\n$FILES"
+
+# create a random filename to store our generated patch
+prefix="static-check-clang-format"
+suffix="$(date +%s)"
+patch="/tmp/$prefix-$suffix.patch"
+
+for file in $FILES; do
+    "$CLANG_FORMAT" -style=file "$file" | \
+        diff -u "$file" - | \
+        sed -e "1s|--- |--- a/|" -e "2s|+++ -|+++ b/$file|" >> "$patch"
+done
+
+# if no patch has been generated all is ok, clean up the file stub and exit
+if [ ! -s "$patch" ] ; then
+    printf "Files in this commit comply with the clang-format rules.\n"
+    rm -f "$patch"
+    exit 0
+fi
+
+# a patch has been created, notify the user and exit
+printf "\n*** The following differences were found between the code to commit "
+printf "and the clang-format rules:\n\n"
+cat "$patch"
+printf "\n*** Aborting, please fix your commit(s) with 'git commit --amend' or 'git rebase -i <hash>'\n"
+exit 1