Fixes #1159: Speed up builds by conditionally "returning early". (#1468)

* Fixes #1159: Speed up builds by conditionally "returning early".

* Fixing yaml syntax.

* Abstracting early exit logic.

* Enclosing command.

Author: grasmash

.travis.yml

@@ -32,6 +32,8 @@ addons:
     - svn-5223.devcloud.hosting.acquia.com
 
 before_install:
+  # Exit build early if only documentation was changed in a Pull Request.
+  - source ${BLT_DIR}/scripts/travis/exit_early
   # Decrypt private SSH key id_rsa_blt.enc, save as ~/.ssh/id_rsa_blt.
   - if [[ "$TRAVIS_PULL_REQUEST" == "false" ]]; then openssl aes-256-cbc -K $encrypted_c0b166e924da_key -iv $encrypted_c0b166e924da_iv -in id_rsa_blt.enc -out ~/.ssh/id_rsa -d; chmod 600 ~/.ssh/id_rsa; ls -lash ~/.ssh; eval "$(ssh-agent -s)"; ssh-add ~/.ssh/id_rsa; fi
   - phpenv config-rm xdebug.ini

scripts/travis/.travis.yml

@@ -43,6 +43,8 @@ notifications:
 # - slack: '<account>:<token>#[channel]'
 
 before_install:
+  # Exit build early if only documentation was changed in a Pull Request.
+  - source ${BLT_DIR}/scripts/travis/exit_early
   # Disable xdebug.
   - phpenv config-rm xdebug.ini
   - composer self-update

scripts/travis/exit_early

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+if ! git diff --name-only $TRAVIS_COMMIT_RANGE | grep -qvE '(\.md$)'
+then
+  echo "Only docs were updated, stopping build process."
+  exit
+fi