THRIFT-4547: add swift to bionic build image and run unit tests
diff --git a/build/docker/ubuntu-bionic/Dockerfile b/build/docker/ubuntu-bionic/Dockerfile
index 4f53ca4..5ad4c84 100644
--- a/build/docker/ubuntu-bionic/Dockerfile
+++ b/build/docker/ubuntu-bionic/Dockerfile
@@ -250,6 +250,13 @@
       cargo \
       rustc
 
+# Swift on Linux for cross tests
+RUN cd / && \
+    wget --quiet https://swift.org/builds/swift-4.2.1-release/ubuntu1804/swift-4.2.1-RELEASE/swift-4.2.1-RELEASE-ubuntu18.04.tar.gz && \
+    tar xf swift-4.2.1-RELEASE-ubuntu18.04.tar.gz --strip-components=1 && \
+    rm swift-4.2.1-RELEASE-ubuntu18.04.tar.gz && \
+    swift --version
+
 # cppcheck-1.82 has a nasty cpp parser bug, so we're using something newer
 RUN apt-get install -y --no-install-recommends \
 `# Static Code Analysis dependencies` \