Fetch a connected sass-spec pull request.

.travis.yml

@@ -17,7 +17,10 @@ install:
 - unzip dart.zip
 - export PATH="$PATH:`pwd`/dart-sdk/bin"
 - pub get
-- git clone git://github.com/sass/sass-spec --branch dart-sass --depth 1
+- SASS_SPEC_REF=`tool/sass-spec-ref.sh`
+- git init sass-spec
+- git -C sass-spec fetch git://github.com/sass/sass-spec "$SASS_SPEC_REF" --depth 1
+- git -C sass-spec checkout FETCH_HEAD
 - (cd sass-spec; bundle install --jobs=3 --retry=3)
 
 script:

tool/sass-spec-ref.sh

@@ -0,0 +1,31 @@
+#!/bin/bash -e
+# Copyright 2016 Google Inc. Use of this source code is governed by an MIT-style
+# license that can be found in the LICENSE file or at
+# https://opensource.org/licenses/MIT.
+
+# Echoes the sass-spec Git ref that should be checked out for the current Travis
+# run. If we're running specs for a pull request which refers to a sass-spec
+# pull request, we'll run against the latter rather than sass-spec master.
+
+default=dart-sass
+
+if [ "$TRAVIS_PULL_REQUEST" == "false" ]; then
+  >&2 echo "Ref: $default."
+  echo "$default"
+  exit 0
+fi
+
+>&2 echo "Fetching pull request $TRAVIS_PULL_REQUEST..."
+
+JSON=$(curl -L -sS https://api.github.com/repos/sass/dart-sass/pulls/$TRAVIS_PULL_REQUEST)
+
+RE_SPEC_PR="sass\/sass-spec(#|\/pull\/)([0-9]+)"
+
+if [[ $JSON =~ $RE_SPEC_PR ]]; then
+  ref="pull/${BASH_REMATCH[2]}/head"
+  >&2 echo "Ref: $ref."
+  echo "$ref"
+else
+  >&2 echo "Ref: $default."
+  echo "$default"
+fi