Bazel watcher

Note: This is not an official Google product.

A source file watcher for Bazel projects

Ever wanted to save a file and have your tests automatically run? How about restart your webserver when one of the source files change? Look no further.

Install ibazel using one of the 3 methods described below. Then:

$ ibazel build //path/to/my:target

Hack hack hack. Save and your target will be rebuilt.

Right now this repo supports build, test, and run.

Installation

There are several ways to install iBazel, documented below.

Mac (Homebrew)

If you run a macOS you can install it from homebrew.

$ brew install ibazel

NPM

If you're a JS developer you can install it as a devDependency or by calling npm install directly in your project

$ npm install @bazel/ibazel

Linux

Packages are available for the following distributions:

• Arch Linux: aur/ibazel

Compiling yourself

You can, of course, build iBazel using Bazel.

$ git clone git@github.com:bazelbuild/bazel-watcher
$ cd bazel-watcher
$ bazel build //cmd/ibazel

Now copy the generated binary onto your path:

$ export PATH=$PATH:$PWD/bazel-bin/cmd/ibazel/ibazel_

Running a target

By default, a target started with ibazel run will be terminated and restarted whenever it's notified of source changes. Alternatively, if the build rule for your target contains ibazel_notify_changes in its tags attribute, then the command will stay alive and will receive a notification of the source changes on stdin.

Output Runner

iBazel is capable of producing and running commands from the output of Bazel commands. If iBazel is run with the flag --run_output then it will check for a %WORKSPACE%/.bazel_fix_commands.json and if present run any commands that match the provided regular expressions. For example the commands defined by the following file will match buildozer commands found in the output and provide a prompt to run the command as well as invoke bazel run //:gazelle if it detects a missing import for your go code.

[
  {
    "regex": "^Check that imports in Go sources match importpath attributes in deps.$",
    "command": "bazel",
    "args": [ "run", "//:gazelle" ]
  },
  {
    "regex": "^buildozer '(.*)'\\s+(.*)$",
    "command": "buildozer",
    "args": [ "$1", "$2" ]
  },
  {
    "regex": "^(\\S+)/[\\w-]+\\.proto:\\d+:\\d+: Import \"\\S+\" was not found or had errors\\.$",
    "command": "bazel",
    "args": [ "run", "//:gazelle", "--", "proto/$1" ]
  }
]

Adding the flag --run_output_interactive=false will automatically run the command without prompting for confirmation. The fields in .bazel_fix_commands.json are:

• regex: a regular expression that will be matched against every line of output.
  • backslash \ characters will need to be escaped once for the regex to be parsed properly.
• command: a command that will be run from the workspace root.
• args: a list of arguments to provide to the command, substituting $1 with the first match group of regex, $2 with the second, etc., and $0 for the entire match.

You can disable this feature by adding flag --run_output=false or you can create a .bazel_fix_commands.json that contains an empty json array, []. This will additionally disable the notification providing usage instructions on the first invocation of iBazel.

Disabling output runner

If you would like to remove the banner but don't wish to configure the output runner, you can create an empty configuration file like this:

echo "[]" > .bazel_fix_commands.json

You should no longer be prompted when iBazel starts up.

Profiling

iBazel has a --profile_dev flag which turns on a generated profile output file about the build process and timing. To use it include this flag in the command line. For example,

ibazel --profile_dev=profile.json run devserver

The profile outfile is in concatenated JSON format. Events are outputted one per line.

Profiler events

Event attributes

Example profile output file

You can find an example profile output JSON file here. Below is the file in pretty print JSON format:

{
  "type": "IBAZEL_START",
  "iteration": "4214114686684e0f",
  "time": 1513706108351,
  "iBazelVersion": "v0.2.0-dirty",
  "bazelVersion": "release 0.8.1-homebrew",
  "maxHeapSize": "3817MB",
  "committedHeapSize": "1372MB"
}
{
  "type": "RUN_START",
  "iteration": "4214114686684e0f",
  "time": 1513706109329,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 978
}
{
  "type": "RELOAD_TRIGGERED",
  "iteration": "4214114686684e0f",
  "time": 1513706114595,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 6244
}
{
  "type": "RUN_DONE",
  "iteration": "4214114686684e0f",
  "time": 1513706114595,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 6244
}
{
  "type": "SOURCE_CHANGE",
  "iteration": "7e6f8e150e9a8367",
  "time": 1513706129384,
  "targets": [
    "//src:devserver"
  ],
  "change": "/Users/greg/google/gregmagolan/angular-bazel-example/src/hello-world/hello-world.component.ts"
}
{
  "type": "RUN_START",
  "iteration": "7e6f8e150e9a8367",
  "time": 1513706129484,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 100,
  "changes": [
    "/Users/greg/google/gregmagolan/angular-bazel-example/src/hello-world/hello-world.component.ts"
  ]
}
{
  "type": "RELOAD_TRIGGERED",
  "iteration": "7e6f8e150e9a8367",
  "time": 1513706133947,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 4563,
  "changes": [
    "/Users/greg/google/gregmagolan/angular-bazel-example/src/hello-world/hello-world.component.ts"
  ]
}
{
  "type": "RUN_DONE",
  "iteration": "7e6f8e150e9a8367",
  "time": 1513706133947,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 4563,
  "changes": [
    "/Users/greg/google/gregmagolan/angular-bazel-example/src/hello-world/hello-world.component.ts"
  ]
}
{
  "type": "REMOTE_EVENT",
  "iteration": "7e6f8e150e9a8367",
  "time": 1513706134297,
  "targets": [
    "//src:devserver"
  ],
  "elapsed": 4913,
  "remoteType": "PAGE_LOAD",
  "remoteTime": 1513706134294,
  "remoteElapsed": 346,
  "remoteData": "{\"pageLoadTime\":344,\"fetchTime\":9,\"connectTime\":0,\"requestTime\":6,\"responseTime\":6,\"renderTime\":325,\"navigationStart\":1513706133948,\"unloadEventStart\":1513706133962,\"unloadEventEnd\":1513706133962,\"redirectStart\":0,\"redirectEnd\":0,\"fetchStart\":1513706133952,\"domainLookupStart\":1513706133952,\"domainLookupEnd\":1513706133952,\"connectStart\":1513706133952,\"connectEnd\":1513706133952,\"secureConnectionStart\":0,\"requestStart\":1513706133955,\"responseStart\":1513706133955,\"responseEnd\":1513706133961,\"domLoading\":1513706133967,\"domInteractive\":1513706134222,\"domContentLoadedEventStart\":1513706134222,\"domContentLoadedEventEnd\":1513706134222,\"domComplete\":1513706134292,\"loadEventStart\":1513706134292}"
}

Remote events

Remote events require the client-side profiling script. If you are using the ts_devserver bazel rule, this script will automatically be included in the development bundle so you don't have to worry about including it. If you're not using ts_devserver for development mode, you can include the following script tag to pull in the client-side profiling script:

<script src="http://localhost:30000/profiler.js"></script>

The script is served by iBazel on port 30000 by default. If port 30000 is not available, iBazel will attempt to find another available port between 30001 and 30099.

Remote events in the profiler script are sent using the Beacon API. This API is available in Chrome 39, Firefox 31, Edge and Opera 26. It is not available in Internet Explorer or Safari. Browser compatability can be checked here.

If your browser does not support the Beacon API, you will see the following error in the console when including the profiler script: iBazel profiler disabled because Beacon API is not available.

Custom remote events

When the profiler script is loaded, a window.IBazelProfileEvent(eventType, data) public API is made available for generating custom remote events. This function sends a custom REMOTE_EVENT to the iBazel profiler log.

Additional notes

Termination

SIGINT has to be sent twice to kill ibazel: once to terminate the subprocess, and the second time for ibazel itself. Also, ibazel will exit on its own when a bazel query fails, but it will stay alive when a build, test, or run fails. We use an exit code of 3 for a signal termination, and 4 for a query failure. These codes are not an API and may change at any point.

What about the --watchfs flag?

Bazel has a flag called --watchfs which, according to the bazel command-line help does:

If true, Bazel tries to use the operating system's file watch service for local changes instead of scanning every file for a change

Unfortunately, this option does not rebuild the project on save like the Bazel watcher does, but instead queries the file system for a list of files that have been invalidated since last build and will require reinspection by the Bazel server.

Big thanks

• Google for cross-platform build/test CI instances.
• Sauce Labs for cross-browser testing.

Copyright 2017 The Bazel Authors. All right reserved.