A Ruby version manager written in Rust, which is 7 seconds faster than rbenv

Link to a slide on Canva

frum: https://github.com/TaKO8Ki/frum
gobang: https://github.com/TaKO8Ki/gobang
Article about frum: https://zenn.dev/tako8ki/articles/2021-09-ruby-version-manager-written-in-rust

I built a Ruby version manager with Rust, which is 7 seconds faster than rbenv. In detail, it takes about 7 seconds faster to install a particular version and set it with frum than rbenv.

Ruby has a lot of code that depends on the runtime version. Therefore, it is important to manage Ruby versions. However, it takes 2 to 3 minutes to run rbenv install, depending on the environment, and waiting for this to happen every time you install a new version is inefficient. The main bottleneck is a command-line utility called ruby-build, which makes it easy to install virtually any version of Ruby. In order to solve this problem, I created a Pure Rust Ruby version manager called frum.

In this talk, I will share my efforts to build a simple and easy to use Ruby version manager with Rust, and what I learned in the process of making frum like the following things.

- Tips on good E2E testing a CLI that manipulates files using declarative macros
- Tips for writing a CLI with multiple subcommands in Rust
- How to use the command line parser clap to implement flexible command-line completion

Q&A

frumはプロダクションでも利用できますか？例えば、今後どのくらいの期間保守が続けられる予定でしょうか？（追記）例えば、moneyforward社で利用予定はありますか？
→
> frumはプロダクションでも利用できますか？例えば、今後どのくらいの期間保守が続けられる予定でしょうか？

プロダクションでの利用はあまり想定していません。例えば、tempdirを利用しているので、ユーザー間でそれが競合してしまうことなどが考えられます。基本的に僕が仕事でRubyを書いている間はメンテする予定なので、少なくとも2、3年は問題ないと思います。基本的にはユーザーがいる限りメンテし続けようとは考えています。

> 例えば、moneyforward社で利用予定はありますか？

基本的に本番環境でバージョンマネージャーを用いたバージョンの切り替えなどは行ってないはずなので、本番環境での利用はしないと思われます。ローカルで使ってくださる方は、もしかしたらいるかもしれないですね。そこら辺は他のOSSと同じで個々の判断で使っていただく形になると思います。

Transcript

1. A Ruby version manager written in
   Rust, which is 7 seconds faster than
   rbenv
   Takayuki Maeda (@TaKO8Ki)
   Rust.Tokyo 2021
   

   View Slide

2. About myself
   

   View Slide

3. About myself
   Takayuki Maeda
   GitHub: @TaKO8Ki
   Twitter: @TaKOBKi
   Software Engineer @ Money Forward, Inc.
   Senior at Kobe University majoring Civil Engineering
   

   View Slide

4. Sometimes contribute to rust-clippy
   

   View Slide

5. I've been building TUI SQL client with Rust
   lately.
   https://github.com/TaKO8Ki/gobang
   

   View Slide

6. View Slide

7. What are rbenv and frum?
   

   View Slide

8. $ rbenv install 2.6.5 # Install a Ruby version using
   ruby-build
   $ rbenv local 2.6.5 # Set or show the local
   application-specific Ruby version
   $ rbenv global 2.6.5 # Set or show the global Ruby
   version
   What is rbenv?
   rbenv is a tool that lets you install and run multiple versions of
   Ruby side-by-side.
   

   View Slide

9. What is ruby-build?
   ruby-build is a command-line utility that makes it easy to install
   virtually any version of Ruby, from source.
   

   View Slide

10. What is frum?
    A little bit fast and modern Ruby version manager written in Rust
    Pure Rust implementation not using ruby-build
    Works with .ruby-version files
    Faster than rbenv
    github.com/TaKO8Ki/frum
    

    View Slide

11. Motivations
    

    View Slide

12. There are many products written in Ruby at
    Money Forward
    

    View Slide

13. You need to wait for 2 to 3 minutes
    every time you install new versions of
    Ruby
    

    View Slide

14. This is not cool
    

    View Slide

15. Of course. There is a limit to how
    much faster I can make installing
    Ruby
    

    View Slide

16. I feel like I can make it about 10
    seconds faster
    

    View Slide

17. Benchmark
    

    View Slide

18. Benchmark
    eval "$(rbenv init -)" → rbenv install → rbenv local
    vs
    eval "$(frum init)" → frum install → frum local
    

    View Slide

19. Benchmark
    frum init vs rbenv init
    

    View Slide

20. What did I improve?
    

    View Slide

21. What did I improve?
    rbenv is written in bash script
    ruby-build is also written in bash script
    rbenv uses shims to switch Ruby versions
    

    View Slide

22. ・rbenv is written in bash script
    ・ruby-build is also written in bash script
    ・rbenv uses shims to switch Ruby versions
    

    View Slide

23. rbenv/libexec
    

    View Slide

24. ・rbenv is written in bash script
    ・ruby-build is also written in bash script
    ・rbenv uses shims to switch Ruby versions
    

    View Slide

25. ruby-build/bin
    ruby-build has 1468 lines
    

    View Slide

26. So do I need to rewrite all of them in
    Rust?
    

    View Slide

27. No. It's not necessary.
    

    View Slide

28. $ ./configure
    $ make
    $ sudo make install
    What to do basically is
    Download source and unpack a tarball, then just do this:
    

    View Slide

29. ./configure
    ⬅︎
    make
    ⬅︎
    

    View Slide

30. make
    ⬅︎
    make install
    ⬅︎
    

    View Slide

31. ・rbenv is written in bash script
    ・ruby-build is also written in bash script
    ・rbenv uses shims to switch Ruby versions
    

    View Slide

32. What is shim?
    > In computer programming, a shim is a small
    library that transparently intercepts API calls and
    changes the arguments passed, handles the
    operation itself, or redirects the operation
    elsewhere.
    https://en.wikipedia.org/wiki/Shim_(computing)
    

    View Slide

33. shims in ~/.rbenv/shims
    

    View Slide

34. View Slide

35. store the command name into $program
    ⬅︎
    

    View Slide

36. store the command name into $program
    ⬅︎
    ⬅︎ setup $RBENV_DIR
    

    View Slide

37. store the command name into $program
    ⬅︎
    ⬅︎ setup $RBENV_DIR
    ⬅︎
    setup $RBENV_ROOT
    rbenv exec
    

    View Slide

38. In case you use Ruby 2.6.5
    rbenv exec ruby -v turns into
    PATH=”~/.rbenv/versions/2.6.5/bin:$PATH”
    ruby -v
    

    View Slide

39. When does rbenv create shims?
    rbenv rehash creates shims. rbenv init runs it internally.
    

    View Slide

40. When does rbenv create shims?
    So what does rbenv rehash do?
    rbenv rehash creates shims. rbenv init runs it internally.
    

    View Slide

41. 1. rbenv rehash checks if the
    directory ~/.rbenv/shims exists
    

    View Slide

42. 2. Rehash checks if
    ~/.rbenv/shims/.rbenv-shim exists
    

    View Slide

43. 3. Rehash creates
    ~/.rbenv/shims/.rbenv-shim and get
    a lock on it
    

    View Slide

44. View Slide

45. 4. Rehash iterates through all files in
    ~/.rbenv/versions/${version}/bin/ of
    all Ruby versions installed. Then, it
    copies prototype file into the shim
    scripts
    

    View Slide

46. 5. Eventually, rehash deletes the
    prototype file
    

    View Slide

47. rbenv runs these steps every time you
    execute rbenv init
    

    View Slide

48. How does frum solve this problem?
    frum uses symlinks to switch Ruby versions.
    src/commands/init.rs
    

    View Slide

49. ⬅︎ generate temp dir
    src/commands/init.rs
    

    View Slide

50. ⬅︎ generate temp dir
    src/commands/init.rs
    ⬅︎
    create a symlink to a Ruby directory
    

    View Slide

51. In short, frum init simply creates a
    symlink
    

    View Slide

52. That results in
    

    View Slide

53. Tips
    

    View Slide

54. Tips for good E2E testing
    Since frum has some subcommands, It is important to
    check if your state is as expected after running multiple
    commands.
    frum init frum install frum local
    ⬅︎
    ⬅︎
    

    View Slide

55. Tips for good E2E testing
    e2e_test macro for E2E testing
    

    View Slide

56. Tips for good E2E testing
    ⬅︎ define a test function
    ⬅︎
    setup
    

    View Slide

57. Tips for good E2E testing
    utils::setup does the following things:
    prepares a temp directory for each test functions
    sets some environment variables frum needs
    

    View Slide

58. Tips for good E2E testing
    If stdout or stderr is not as expected, the error is
    displayed like the following:
    

    View Slide

59. Tips to create CLI with multiple
    subcommands
    

    View Slide

60. View Slide

61. ⬅︎
    function you need to implement
    

    View Slide

62. View Slide

63. --ruby-build-mirror
    ⬅︎
    

    View Slide

64. ⬅︎
    Custom Error Type
    

    View Slide

65. ⬅︎
    Custom Error Type
    ⬅︎install command arguments
    

    View Slide

66. ⬅︎
    Custom Error Type
    ⬅︎install command arguments
    ⬅︎
    return custom error
    

    View Slide

67. Tips to implement flexible
    Command-line completion using
    clap
    

    View Slide

68. Tips to implement flexible
    Command-line completion using
    clap
    You can implement completion using
    clap::App::gen_completions
    However it is not useful enough
    

    View Slide

69. That is because
    clap doesn't support adding additional code to complete
    values.
    

    View Slide

70. That is because
    clap doesn't support adding additional code to complete
    values.
    

    View Slide

71. In frum ⬅︎ prepare a empty vector
    

    View Slide

72. In frum ⬅︎ prepare a empty vector
    store completions into buffer
    ⬅︎
    

    View Slide

73. In frum ⬅︎ prepare a empty vector
    store completions into buffer
    ⬅︎
    ⬅︎
    iterating over lines in completions
    

    View Slide

74. In frum
    

    View Slide

75. In frum
    

    View Slide

76. Conclusions
    

    View Slide

77. Conclusions
    frum install runs a little bit faster than rbenv install
    frum init runs about 6x faster than rbenv init
    

    View Slide

78. View Slide