Debugging Rails Itself - Speaker Deck

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Please sit as close to the front and center as possible

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Story Time

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Story Time

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Debugging Rails Itself

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TL;DR: Make Aaron ﬁx it

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Thank you

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Debugging Rails Itself

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Who am I? • Sean Grifﬁn • 10x Hacker Ninja Guru at Shopify • @sgrif on Twitter (please tweet at me during this talk) • Rails Committer • Maintainer of Active Record • Creator of Diesel • Bikeshed co-host

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Anyone can work on Rails

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Do we have a bug in Rails?

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What even is a bug?

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Expectations vs reality

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Features aren't always used as designed

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Check the docs

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We think it's a bug. What's next?

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We need a reproducible test case

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gemfile(true) do source "https://rubygems.org" git_source(:github) { |repo| "https://github.com/#{repo}.git" } gem "rails", github: "rails/rails" gem "sqlite3" end

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ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:") ActiveRecord::Base.logger = Logger.new(STDOUT) ActiveRecord::Schema.define do create_table :posts, force: true do |t| end create_table :comments, force: true do |t| t.integer :post_id end end

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class BugTest < Minitest::Test def test_association_stuff post = Post.create! post.comments << Comment.create! assert_equal 1, post.comments.count assert_equal 1, Comment.count assert_equal post.id, Comment.first.post.id end end

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The bug needs to be demonstrated with no gems other than Rails

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Now what?

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It's time to go bug hunting

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We need the commit that introduced the bug

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git bisect (the greatest tool ever)

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Changing our test script ENV["BUNDLE_GEMFILE"] = "/path/to/rails/Gemfile" require "bundler" Bundler.require

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Bisecting basics git checkout master git bisect start git bisect bad git checkout 4-2-stable git bisect good

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Even if you don't ﬁx the bug, bisecting is incredibly useful

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What if there's no version without the bug?

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I'm a dinosaur debugger

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Methods you should know • Kernel#method

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(Some objects override the method method) Kernel .instance_method(:method) .bind(self) .call

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Other methods besides the method method • Kernel#method • Method#source_location • Method#super_method • Method#method

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Methods unrelated to the method method • Kernel#caller • Kernel#raise • Kernel#p

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git blame

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git blame context

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How to not blame people # ~/.gitconfig [alias] context = blame

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GitHub's UI is helpful for recontexting

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gif of how to use it

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Why do we care so much about the commit?

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Time to ﬁx it!

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I'm Stuck

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Take a Break

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Find a Pair

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When you ﬁnally ﬁx it

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Anyone can work on Rails

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Want more Ruby?

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Room 315 2:30 PM

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Please ask me questions now

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Contact • twitter: @sgrif • github: @sgrif • podcast: bikeshed.fm