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

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

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About myself

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

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Sometimes contribute to rust-clippy

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

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What are rbenv and frum?

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$ 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.

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

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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

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Motivations

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There are many products written in Ruby at Money Forward

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

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This is not cool

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

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I feel like I can make it about 10 seconds faster

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Benchmark

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

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Benchmark frum init vs rbenv init

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What did I improve?

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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

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

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rbenv/libexec

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

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ruby-build/bin ruby-build has 1468 lines

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

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No. It's not necessary.

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

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./configure ⬅︎ make ⬅︎

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make ⬅︎ make install ⬅︎

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

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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)

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shims in ~/.rbenv/shims

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store the command name into $program ⬅︎

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

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

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

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

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

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

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

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

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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

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5. Eventually, rehash deletes the prototype file

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rbenv runs these steps every time you execute rbenv init

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

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⬅︎ generate temp dir src/commands/init.rs

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

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In short, frum init simply creates a symlink

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That results in

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Tips

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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 ⬅︎ ⬅︎

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Tips for good E2E testing e2e_test macro for E2E testing

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

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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

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

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Tips to create CLI with multiple subcommands

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⬅︎ function you need to implement

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--ruby-build-mirror ⬅︎

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⬅︎ Custom Error Type

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⬅︎ Custom Error Type ⬅︎install command arguments

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

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Tips to implement flexible Command-line completion using clap

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

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

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

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In frum ⬅︎ prepare a empty vector

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

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

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In frum

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In frum

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Conclusions

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

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