Add Bazel job in Travis (#395)

* Add a new matrix cell for [Bazel](https://bazel.build)
* In the bazel job:
  - install deps with apt
  - download bazel.deb from official repo
  - install with `sudo apt-get install`. **N.B.** This job needs **sudo: true**
* Add a simple `bazel.sh` that only does (and it's not going to change much in the future)
  ```
  cd jflex/examples
  bazel build //...
  bazel test //...
  ```
* Add an (virtually) empty root `jflex/examples/BUILD`
  - This root BUILD defines one sh_test, so that `bazel test //...` doesn't complain with 
    > No test targets were found, yet testing was requested
* This is the first step for #204 (Bazel support)
* **N.B.** Do not use a cache for bazel.
  - I tried caching the bazel output directory (this is in theory perfectly fine)
    by setting  a non-default `--output_user_root=$TRAVIS_BUILD_DIR/__bazel__`
  - But the VM hangs at startup with
    > creating directory /home/travis/build/jflex-de/jflex/__bazel__

.travis.bazelrc

@@ -0,0 +1,9 @@
+# This is from Bazel's former travis setup, to avoid blowing up the RAM usage.
+startup --host_jvm_args=-Xms2000m
+startup --host_jvm_args=-Xmx3000m
+test --ram_utilization_factor=10
+
+# This is so we understand failures better
+build --verbose_failures
+test  --test_output=errors
+

.travis.yml

@@ -31,6 +31,29 @@ matrix:
     sdk: oraclejdk8
   - name: "Ant JDK9"
     script: scripts/run-ant.sh
+  - name: "Bazel"
+    script: scripts/bazel.sh
+    # Prerequisites for Bazel
+    addons:
+      apt:
+        sources:
+          - ubuntu-toolchain-r-test
+        packages:
+          - curl
+          - pkg-config
+          - zip
+          - g++
+          - zlib1g-dev
+          - unzip
+          - python
+    before_install:
+    - mkdir -p tools
+    - curl -L https://github.com/bazelbuild/bazel/releases/download/0.16.1/bazel_0.16.1-linux-x86_64.deb -o tools/bazel-0.16.1.deb
+    install:
+    - java -version
+    - sudo apt-get install ./tools/bazel-0.16.1.deb
+    sudo: true
+    after_success: blaze shutdown
 
 # Empty the previously built artifacts
 # They cannot be deleted in the before_cache phase,

jflex/examples/.gitignore

@@ -1,3 +1,3 @@
-build
+antbuild
 target
 out

jflex/examples/BUILD

@@ -0,0 +1,24 @@
+# Root bazel package
+
+# This pacakge exists because
+# `bazel build //...` needs at least one package
+
+# But bazel test //... fails with
+# No test targets were found, yet testing was requested
+# So here is a test:
+
+sh_test(
+  name = "hello_test",
+  size = "small",
+  srcs = [":hello_test_lib"],
+)
+sh_library(
+  name = "hello_test_lib",
+  srcs = [":gen_hello_test_sh"],
+)
+genrule(
+  name = "gen_hello_test_sh",
+  srcs = [],
+  outs = ["hello_test.sh"],
+  cmd = "echo 'echo \"Hello World\"' > $@",
+)

jflex/examples/WORKSPACE

@@ -0,0 +1 @@
+

scripts/bazel.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# Run bazel on examples
+
+CWD="$PWD"
+BASEDIR="$(cd "$(dirname "$0")" && pwd -P)"/..
+# Provides the logi function
+source "$BASEDIR"/scripts/logger.sh
+# fail on error
+set -e
+
+if [[ $TRAVIS ]]; then
+  BAZEL="bazel --bazelrc=$TRAVIS_BUILD_DIR/.travis.bazelrc"
+else
+  BAZEL='bazel'
+fi
+
+logi "Start Bazel"
+logi "==========="
+cd jflex/examples
+$BAZEL info
+
+logi "Build everything"
+logi "================"
+$BAZEL build //...
+
+logi "Test everything"
+logi "==============="
+$BAZEL test //...
+
+cd "$CWD"

scripts/run-tests.sh

@@ -31,6 +31,9 @@ if [[ -z "$TEST_SUITE" || "$TEST_SUITE" == "ant" ]]; then
   "$BASEDIR"/scripts/ant-build.sh
   "$BASEDIR"/scripts/test-examples.sh
 fi
+if [[ -z "$TEST_SUITE" || "$TEST_SUITE" == "bazel" ]]; then
+  "$BASEDIR"/scripts/bazel.sh
+fi
 
 logi "Success"
 cd "$CWD"