Format Your Elixir Code Now

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Format Your Elixir Code Now Jake Worth, Hashrocket

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"Elixir master now includes a code formatter that automatically formats your code according to a consistent style. We want to convert Elixir's codebase to use the formatter on all files. We understand this means a lot of code churn now but, on the positive side, it means we can automatically enforce and/or format future contributions, making it easier for everyone to contribute to Elixir."1 1 José Valim, Github Elixir-Lang Issue #6643, https://github.com/elixir-lang/elixir/issues/6643. 3

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Refactor Stats » 425 files changed » 214 pull requests » 84 committers » 368 commits » 4 days to complete! 4

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@jwworth Hashrocket 5

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A Changing Community » Before v1.6: style is subjective » After v1.6: style conforms to a community style guide 7

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Questions » What is autoformatting? » Why should I care? » What is it going to do to my code? 8

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Format your code now. It's where Elixir is headed. 9

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Agenda 1. History of Autoformatting 2. Arguments For/Against 3. Practical Applications 10

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Slides » https://speakerdeck.com/jwworth (PDF) 11

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1. History of Autoformatting 12

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Autoformat: to cause the layout of a document to be created or edited without further effort by the execution of a program.2 2 Your Dictionary, http://www.yourdictionary.com/, s.v. "Autoformat". 13

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Linting vs. Autoformatting Tool Target Action Linter Code smells Recommends changes Autoformatter Inconsistent style Recommends + changes code 14

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Theory: Autoformatting solves a modern problem 16

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Go + Autoformatting » Go created in 2009 » gofmt released in 2013 » Overview: https:// blog.golang.org/go-fmt-your- code 17

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Autoformatted Go Easier to write: never worry about minor formatting concerns while hacking away 18

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Autoformatted Go Easier to read: when all code looks the same you need not mentally convert others' formatting style into something you can understand 19

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Autoformatted Go Easier to maintain: mechanical changes to the source don't cause unrelated changes to the file's formatting; diffs show only the real changes 20

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Autoformatted Go Uncontroversial: never have a debate about spacing or brace position ever again! 21

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Elixir + Autoformatting » Elixir created in 2011 » mix format released in Elixir 1.6 (January 2018) » Overview: José Valim's ElixirConf 2017 keynote 22

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We don't talk about these anymore 24

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2. Arguments For/ Against 25

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Arguments For/Against For Against Productivity But My Preferences! Consistency Friendliness to Newcomers Execution 26

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For: Productivity Bikeshedding [originally BSD, now common] Technical disputes over minor, marginal issues conducted while more serious ones are being overlooked. The implied image is of people arguing over what color to paint the bicycle shed while the house is not finished.4 » Most style preferences don't matter 4 The Jargon File (version 4.4.7), http://www.catb.org/, s.v. "Bikeshedding". 27

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For: Consistency » Elixir should have "a consistent style" » Distinct style guides separate us » We need "collective ownership" of the community's code 28

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Eliminate Trivial Decisions 30

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For: Friendliness to Newcomers » New devs shouldn't have to learn "how things are done here" on every team » Elixir code should be exemplary » Feedback on your code need not always come from a human 31

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For: Execution Elixir Autoformatter's Guidelines:5 1. It does not change code semantics by default 2. Minimizes configuration 3. No special cases 5 José Valim, "Elixir Conf Keynote 2017", https://www.youtube.com/watch?v=Wa7Ipc0yo (Accessed 7 Feb 2018) 32

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Against: But My Preferences! » Elixir's formatter always removes "trailing commas" » "No trailing comma (ever)."6 6 José Valim, 'Elixir Style Guide Pull Request #46', https://github.com/lexmag/elixir-style-guide/pull/46. 33

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Trailing Comma Controversy [ 1, 2 ] [ 1, 2, ] 34

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Trailing Comma Controversy [ 1, 2 ] [ 1, 2, ] 35

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I came, I saw, I conquered. 36

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I came, I saw, I conquered,. 37

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Trailing Comma Controversy [ 1, 2 ] ‑ [ 1, 2, 3 ] 38

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Trailing Comma Controversy [ 1, 2 ] ‑ [ 1, 2, 3 ] 39

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Trailing Comma Controversy [ 1, 2, ] ‑ [ 1, 2, 3, ] 40

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Trailing Comma Controversy [ 1, 2, ] ‑ [ 1, 2, 3, ] 41

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Against: But My Preferences! Potential Benefit: If successful, it ends persistent debates 42

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Any code of your own that you haven't looked at for six or more months might as well have been written by someone else. — Eagleson's Law 43

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3. Practical Applications 44

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TIL Stats » 90 Total (non-dependency) Elixir files » 31 files (35%) passed the formatter » Conclusion: churn is coming 47

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# lib/tilex_web/controllers/post_controller.ex plug :load_channels when action in [:new, :create, :edit, :update] 48

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# lib/tilex_web/controllers/post_controller.ex plug :load_channels when action in [:new, :create, :edit, :update] ‑ plug(:load_channels when action in [:new, :create, :edit, :update]) 49

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# lib/tilex_web/controllers/post_controller.ex page = params |> Map.get("page", "1") |> String.to_integer 50

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# lib/tilex_web/controllers/post_controller.ex page = params |> Map.get("page", "1") |> String.to_integer ‑ page = params |> Map.get("page", "1") |> String.to_integer() 51

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# lib/tilex_web/controllers/post_controller.ex render(conn, "search_results.html", posts: posts, posts_count: posts_count ) 52

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‑ render( conn, "search_results.html", posts: posts, posts_count: posts_count ) 53

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# lib/tilex_web/controllers/post_controller.ex post = case current_user.admin do false -> current_user |> assoc(:posts) |> Repo.get_by!(slug: slug) true -> Repo.get_by!(Post, slug: slug) end 54

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‑ post = case current_user.admin do false -> current_user |> assoc(:posts) |> Repo.get_by!(slug: slug) true -> Repo.get_by!(Post, slug: slug) end 55

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# lib/tilex_web/router.ex @auth_controller Application.get_env(:tilex, :auth_controller) @cors_origin Application.get_env(:tilex, :cors_origin) 56

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# lib/tilex_web/router.ex @auth_controller Application.get_env(:tilex, :auth_controller) @cors_origin Application.get_env(:tilex, :cors_origin) ‑ @auth_controller Application.get_env(:tilex, :auth_controller) @cors_origin Application.get_env(:tilex, :cors_origin) 57

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# config/config.exs config :guardian, Guardian, allowed_algos: ["HS512"], # optional 58

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# config/config.exs config :guardian, Guardian, allowed_algos: ["HS512"], # optional ‑ config :guardian, Guardian, # optional allowed_algos: ["HS512"], 59

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CI Integration # .circleci/conﬁg.yml steps: - mix format --check-formatted 60

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Text Editor Integrations Vim: " ~/.vimrc autocmd BufWritePost *.exs,*.ex silent :!mix format --check-equivalent % 61