Category: emacs

Hacking on rails using emacs

Rails contributor?

Apparently I committed to rails before, I’m pretty sure it was a doc update, but none the less this is something I actually like to do more. So first step get a working setup for running rails tests locally and getting a reasonably productive environment setup. Since I’m mostly using emacs these days it would be nice if everything would actually work out of this editor/operating system.

rake test

The easiest way to run the tests after cloning down rails and bundling is to use rake.

$ bundle exec rake test

in the root rails folder will run all the available tests, this is great but when working on something also not what I want most of the time. But running it in a subfolder like activesupport will actually do the right thing and run only this subset of tests

$ cd activesupport 
$ bundle exec rake test

To make this easier I’m using textmate.el to execute most commands while inside a project from the determined project-root. Meaning if I switch to a file I set the working directory to the current root automatically.

(defun coder/default-project-dir ()
  (if (textmate-project-root)
      (setq default-directory (textmate-project-root))))

(add-hook 'find-file-hook 'coder/default-project-dir)

Adding .emacs-project files to all the subdirectories will now make sure that when I run a rake command it will be run in the correct directory. Combining this with rake.el allows to run test via a simple M-x rake and selecting test, M-x rake-rerun will now rerun the given tests with a simple command.

This works great while working in quick running test suites but running the whole suite on every change can become inconvenient quickly, this is solved by 2 more enhancements to the flow

running a single test file

Rake allows for passing a file name to limit the run to a single test file

$ bundle exec rake test TEST="test/abstract/callbacks_test.rb"

for example will run only this file of the actionpack testsuite for example. Make sure to run with bundle exec, rake.el does not detect this when in a subfolder, but C-u M-x rake will let you modify the command as needed.

running a single test

Should a file have a lot of tests it can be a good idea to only run a single one, this is possible by passing an option to the minitest testrunner.

$ bundle exec rake test TEST="test/abstract/callbacks_test.rb" TESTOPTS="--name=test_around_action_works"

TESTOPTS will be passed through to minitest which will only run this one test.

integration in emacs

All this works on the command line, as well as using rake.el, personally I use rake.el and have rake rerun bound to C-c r to allow me to quickly run the tests I’m currently working on, this executes in compilation-mode, which allows emacs to parse out file urls and makes them clickable in case of errors.

Next up to make it even better would be to figure out the test name I’m currently in, this works quite simply for files which use the

class TestClass < Minitest::Testcase
  def test_foo
    assert_true doing_the_foo

syntax, but is much harder with files

class TestClass < Minitest::Testcase
  test "doing the foo" do
    assert_true doing_the_foo

So for now I stick with doing it by hand.

How to remember circuit breaker configuration with Emacs

Some things are just not easy to remember and looking them up, saving a bookmark to wherever, is just tedious. So how about saving a bookmark and at the same time automating the calculation? Well this is why I started a file which hopefully grows with all those little formulas, using the lisp docstrong to provide a note and a link to why this is relevant.

First thing, when configuring a circuit breaker we need to set a size for how many parallel requests we want to accept, luckily Netflix has a nice formula for this, and even more lucky it is documented on the yammer tenacity repository.

(defun hysterix/thread-pool-size (p99 reqs)
  "calculate and insert the thread pool size for a hysterix
circuit based on the p99 and the requests per secound see for
more details"
  (interactive "nP99 in ms:
nRequests per sec: ")
  (let ((thread-pool-size (ceiling (* (/ (float p99) 1000.0) reqs))))
    (insert (format "%d" thread-pool-size))))

All I need to do now when configuring a circuit, hit M-x hysterix/thread-pool-size and insert the 99th percentile for request latency I can easily get from the service monitoring, as well as the requests per second. If ever in doubt I can use C-h f hysterix/thread-pool-size to get the documentation.

Creating Pull Requests quickly from Emacs

A lot of code I work on lives in GitHub, both work and personal project normally make their way there quickly so maintaining it means I work with the GitHub interface quite a lot as well. To make my live a little easier I decided to create a quick Emacs function to drop me in the matching interface and create or visit the pull request I’m currently working on. Luckily most of the pieces where already out there. All that was needed was grabbing the correct URL and branch from the current repository.

Switching git users in Emacs based on repository

Using Github internally for work is really nice, but especially when working on multiple projects, some on public and some on internal Github it can also be quite hard to always remember to use the correct username and email for the commits. Because I tend to forget such things I decided to create a little elisp function to make sure the correct user is set when I start magit. Right now I only have to switch between 2 users so it is managable, but I think this is easily extended to more if the need arises (god I hope not).