Travis - Only run tests that have changed

.travis.yml

@@ -53,3 +53,4 @@ after_success:
 branches:
   only:
   - master
+  - travis-run-changed

travis.sh

@@ -23,8 +23,44 @@ SKIP_TESTS=false
 if [ -z "$GOOGLE_APPLICATION_CREDENTIALS" ] ; then
   SKIP_TESTS=true
 fi
+
+# Finds the closest parent dir that encompasses all changed files, and has a
+# pom.xml
+travis_changed_files_parent() {
+  [ -z "$TRAVIS_PULL_REQUEST" ] && return 0  # If we're not in a PR, forget it
+
+  (
+    set +e
+
+    changed="$(git diff --name-only "$TRAVIS_COMMIT" "$TRAVIS_BRANCH")"
+    if [ $? -ne 0 ]; then
+      # Fall back to git head
+      changed="$(git diff --name-only "$(git rev-parse HEAD)" "$TRAVIS_BRANCH")"
+      [ $? -ne 0 ] && return 0  # Give up. Just run everything.
+    fi
+
+    # Find the common prefix
+    prefix="$(echo "$changed" | sed -e 'N;s/^\(.*\).*\n\1.*$/\1\n\1/;D')"
+
+    while [ ! -z "$prefix" ] && [ ! -r "$prefix/pom.xml" ] && [ "${prefix%/*}" != "$prefix" ]; do
+      prefix="${prefix%/*}"
+    done
+
+    [ -r "$prefix/pom.xml" ] || return 0
+
+    echo "$prefix"
+  )
+}
+
+travis_changed_files_parent
+common_travis_dir="$(travis_changed_files_parent)"
+
+[ -z "$common_travis_dir" ] || pushd "$common_travis_dir"
+
 mvn --batch-mode clean verify -DskipTests=$SKIP_TESTS | egrep -v "(^\[INFO\] Download|^\[INFO\].*skipping)"
 
+[ -z "$common_travis_dir" ] || popd
+
 # Check that all shell scripts in this repo (including this one) pass the
 # Shell Check linter.
 shellcheck ./**/*.sh
@@ -44,7 +80,9 @@ test_localhost() {
       appengine/datastore/indexes-perfect
   )
   for testdir in "${devserver_tests[@]}" ; do
-    ./java-repo-tools/scripts/test-localhost.sh appengine "${testdir}"
+    if [ -z "$common_travis_dir" ] || [[ $testdir = $common_travis_dir* ]]; then
+      ./java-repo-tools/scripts/test-localhost.sh appengine "${testdir}"
+    fi
   done
 
   # newplugin_std_tests=(