Fix issue where TRAVIS_BRANCH incorrectly specifies the branch name on PRs

Author: josegonzalez

.travis.yml

@@ -8,6 +8,7 @@ php:
   - 7.0
 
 before_install:
+  - source tests/travis-github-pr-integration.sh
   - if [ -f .git/shallow ]; then rm .git/shallow; fi
   - composer install
   - composer require --prefer-source --dev squizlabs/php_codesniffer:~2.0

tests/travis-github-pr-integration.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+# Return if we are not in a Pull Request
+[[ "$TRAVIS_PULL_REQUEST" = "false" ]] && return
+
+GITHUB_PR_URL=https://api.github.com/repos/$TRAVIS_REPO_SLUG/pulls/$TRAVIS_PULL_REQUEST
+GITHUB_PR_BODY=$(curl -s $GITHUB_PR_URL 2>/dev/null)
+
+if [[ $GITHUB_PR_BODY =~ \"ref\":\ *\"([a-zA-Z0-9_-]*)\" ]]; then
+  export TRAVIS_PR_BRANCH=${BASH_REMATCH[1]}
+else
+  return
+fi
+
+GITHUB_BRANCH_URL=https://api.github.com/repos/$TRAVIS_REPO_SLUG/branches/$TRAVIS_PR_BRANCH
+if [ $(curl -s --head  --request GET $GITHUB_BRANCH_URL | grep "200 OK" > /dev/null) ]; then
+  TRAVIS_BRANCH=$TRAVIS_PR_BRANCH
+  if [[ $GITHUB_PR_BODY =~ \"repo\":.*\"clone_url\":\ *\"https://github\.com/([a-zA-Z0-9_-]*/[a-zA-Z0-9_-]*)\.git.*\"base\" ]]; then
+    export TRAVIS_REPO_SLUG=${BASH_REMATCH[1]}
+  fi
+fi