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？
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> 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
2. About myself
3. About myself Takayuki Maeda GitHub: @TaKO8Ki Twitter: @TaKOBKi Software Engineer @ Money Forward, Inc. Senior at Kobe University majoring Civil Engineering
4. Sometimes contribute to rust-clippy
5. I've been building TUI SQL client with Rust lately. https://github.com/TaKO8Ki/gobang
7. What are rbenv and frum?
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.
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.
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
11. Motivations
12. There are many products written in Ruby at Money Forward
13. You need to wait for 2 to 3 minutes every time you install new versions of Ruby
14. This is not cool
15. Of course. There is a limit to how much faster I can make installing Ruby
16. I feel like I can make it about 10 seconds faster
17. Benchmark
18. Benchmark eval "$(rbenv init -)" → rbenv install → rbenv local vs eval "$(frum init)" → frum install → frum local
19. Benchmark frum init vs rbenv init
20. What did I improve?
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
22. ・rbenv is written in bash script ・ruby-build is also written in bash script ・rbenv uses shims to switch Ruby versions
23. rbenv/libexec
24. ・rbenv is written in bash script ・ruby-build is also written in bash script ・rbenv uses shims to switch Ruby versions
25. ruby-build/bin ruby-build has 1468 lines
26. So do I need to rewrite all of them in Rust?
27. No. It's not necessary.
28. $ ./configure $ make $ sudo make install What to do basically is Download source and unpack a tarball, then just do this:
29. ./configure ⬅︎ make ⬅︎
30. make ⬅︎ make install ⬅︎
31. ・rbenv is written in bash script ・ruby-build is also written in bash script ・rbenv uses shims to switch Ruby versions
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)
33. shims in ~/.rbenv/shims
35. store the command name into $program ⬅︎
36. store the command name into $program ⬅︎ ⬅︎ setup $RBENV_DIR
37. store the command name into $program ⬅︎ ⬅︎ setup $RBENV_DIR ⬅︎ setup $RBENV_ROOT rbenv exec
38. In case you use Ruby 2.6.5 rbenv exec ruby -v turns into PATH=”~/.rbenv/versions/2.6.5/bin:$PATH” ruby -v
39. When does rbenv create shims? rbenv rehash creates shims. rbenv init runs it internally.
40. When does rbenv create shims? So what does rbenv rehash do? rbenv rehash creates shims. rbenv init runs it internally.
41. 1. rbenv rehash checks if the directory ~/.rbenv/shims exists
42. 2. Rehash checks if ~/.rbenv/shims/.rbenv-shim exists
43. 3. Rehash creates ~/.rbenv/shims/.rbenv-shim and get a lock on it
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
46. 5. Eventually, rehash deletes the prototype file
47. rbenv runs these steps every time you execute rbenv init
48. How does frum solve this problem? frum uses symlinks to switch Ruby versions. src/commands/init.rs
49. ⬅︎ generate temp dir src/commands/init.rs
50. ⬅︎ generate temp dir src/commands/init.rs ⬅︎ create a symlink to a Ruby directory
51. In short, frum init simply creates a symlink
52. That results in
53. Tips
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 ⬅︎ ⬅︎
55. Tips for good E2E testing e2e_test macro for E2E testing
56. Tips for good E2E testing ⬅︎ define a test function ⬅︎ setup
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
58. Tips for good E2E testing If stdout or stderr is not as expected, the error is displayed like the following:
59. Tips to create CLI with multiple subcommands
61. ⬅︎ function you need to implement
63. --ruby-build-mirror ⬅︎
64. ⬅︎ Custom Error Type
65. ⬅︎ Custom Error Type ⬅︎install command arguments
66. ⬅︎ Custom Error Type ⬅︎install command arguments ⬅︎ return custom error
67. Tips to implement flexible Command-line completion using clap
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
69. That is because clap doesn't support adding additional code to complete values.
70. That is because clap doesn't support adding additional code to complete values.
71. In frum ⬅︎ prepare a empty vector
72. In frum ⬅︎ prepare a empty vector store completions into buffer ⬅︎
73. In frum ⬅︎ prepare a empty vector store completions into buffer ⬅︎ ⬅︎ iterating over lines in completions
74. In frum
75. In frum
76. Conclusions
77. Conclusions frum install runs a little bit faster than rbenv install frum init runs about 6x faster than rbenv init