sneak-preview-writing-ruby-gem-native-extensions-in-rust

000.sh

$ git clone --branch cargo-builder git@github.com:ianks/rubygems.git
Cloning into 'rubygems'...
remote: Enumerating objects: 224785, done.
remote: Counting objects: 100% (5/5), done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 224785 (delta 3), reused 3 (delta 3), pack-reused 224780
Receiving objects: 100% (224785/224785), 191.82 MiB | 38.18 MiB/s, done.
Resolving deltas: 100% (124370/124370), done.

$ cd rubygems

001.sh

export RUBYGEMS_PATH="$(pwd)"
alias gem="ruby -I$RUBYGEMS_PATH/lib $RUBYGEMS_PATH/bin/gem"
alias bundle="ruby $RUBYGEMS_PATH/bundler/spec/support/bundle.rb"

002.sh

$ gem --version
3.4.0.dev

$ bundler --version
Bundler version 2.4.0.dev

003.sh

$ git clone https://github.com/briankung/rust_ruby_example
$ cd rust_ruby_example

004.sh

$ gem build rust_ruby_example.gemspec --output rust_ruby_example.gem
WARNING:  licenses is empty, but is recommended.  Use a license identifier from
http://spdx.org/licenses or 'Nonstandard' for a nonstandard license.
WARNING:  no homepage specified
WARNING:  See https://guides.rubygems.org/specification-reference/ for help
  Successfully built RubyGem
  Name: rust_ruby_example
  Version: 0.1.0
  File: rust_ruby_example.gem

005.sh

$ gem install rust_ruby_example.gem
Building native extensions. This could take a while...
Successfully installed rust_ruby_example-0.1.0
1 gem installed

006.sh

$ gem install rust_ruby_example.gem
Building native extensions. This could take a while...
ERROR:  Error installing rust_ruby_example.gem:
    ERROR: Failed to build gem native extension.

    current directory: /Users/brian/.rbenv/versions/3.0.0/lib/ruby/gems/3.0.0/gems/rust_ruby_example-0.1.0
cargo rustc --target-dir /Users/brian/.rbenv/versions/3.0.0/lib/ruby/gems/3.0.0/extensions/x86_64-darwin-21/3.0.0/rust_ruby_example-0.1.0 --manifest-path /Users/brian/.rbenv/versions/3.0.0/lib/ruby/gems/3.0.0/gems/rust_ruby_example-0.1.0/Cargo.toml --lib --release --locked -- -C linker\=clang -C link-arg\=-fdeclspec -L native\=/Users/brian/.rbenv/versions/3.0.0/lib -L native\=/Users/brian/.rbenv/versions/3.0.0/lib -L native\=/usr/local/opt/icu4c/lib -C link_arg\=-Wl,-undefined,dynamic_lookup -C link_arg\=-Wl,-multiply_defined,suppress -C debuginfo\=1
cargo failedNo such file or directory - cargo

Gem files will remain installed in /Users/brian/.rbenv/versions/3.0.0/lib/ruby/gems/3.0.0/gems/rust_ruby_example-0.1.0 for inspection.
Results logged to /Users/brian/.rbenv/versions/3.0.0/lib/ruby/gems/3.0.0/extensions/x86_64-darwin-21/3.0.0/rust_ruby_example-0.1.0/gem_make.out

007.sh

$ gem install rust_ruby_example.gem
Building native extensions. This could take a while...
ERROR:  Error installing rust_ruby_example.gem:
    ERROR: Failed to build gem native extension.

    No builder for extension 'Cargo.toml'

Gem files will remain installed in /Library/Ruby/Gems/2.6.0/gems/rust_ruby_example-0.1.0 for inspection.
Results logged to /Library/Ruby/Gems/2.6.0/extensions/universal-darwin-21/2.6.0/rust_ruby_example-0.1.0/gem_make.out

008.rs

#[no_mangle]
unsafe extern "C" fn pub_reverse(_klass: VALUE, mut input: VALUE) -> VALUE {
    let ruby_string = cstr_to_string(rb_string_value_cstr(&mut input));
    let reversed = ruby_string.to_string().chars().rev().collect::<String>();
    let reversed_cstring = CString::new(reversed).unwrap();
    let size = ruby_string.len() as c_long;

    rb_utf8_str_new(reversed_cstring.as_ptr(), size)
}

009.rs

let reversed = ruby_string.to_string().chars().rev().collect::<String>();

010.rs

let name = CString::new("RustRubyExample").unwrap();
// ...
let klass = unsafe { rb_define_module(name.as_ptr()) };

011.rs

// Name of the function
let function_name = CString::new("reverse").unwrap();

// transmute the function for unknown reasons
let callback = unsafe {
    std::mem::transmute::<
        unsafe extern "C" fn(VALUE, VALUE) -> VALUE,
        unsafe extern "C" fn() -> VALUE,
    >(pub_reverse)
};
// ...Bind the transmuted function as a module function on the RustRubyExample module
unsafe { rb_define_module_function(klass, function_name.as_ptr(), Some(callback), 1) }

012.sh

$ gem install rust_ruby_example.gem
Building native extensions. This could take a while...
Successfully installed rust_ruby_example-0.1.0
1 gem installed

013.sh

$ irb
irb(main):001:0' require 'rust_ruby_example'
=> true
irb(main):002:0> RustRubyExample.reverse("rust_ruby_example")
=> "elpmaxe_ybur_tsur"

014.sh

$ irb
irb(main):001:0' require 'rust_ruby_example'
=> true
irb(main):002:0> RustRubyExample.lowercase("RustRubyExample")
=> "rustrubyexample"

015.sh

$ irb
irb(main):001:0> require 'rust_ruby_example'
=> true
irb(main):002:0> RustRubyExample.lowercase("RustRubyExample")
Traceback (most recent call last):
        4: from /Users/brian/.rbenv/versions/3.0.0/bin/irb:23:in `<main>'
        3: from /Users/brian/.rbenv/versions/3.0.0/bin/irb:23:in `load'
        2: from /Users/brian/.rbenv/versions/3.0.0/lib/ruby/gems/3.0.0/gems/irb-1.3.0/exe/irb:11:in `<top (required)>'
        1: from (irb):2:in `<main>'
NoMethodError (undefined method `lowercase' for RustRubyExample:Module)

016.rs

// in src/lib.rs

#[no_mangle]

017.rs

// in src/lib.rs

#[no_mangle]
unsafe extern "C" fn pub_lowercase(_klass: VALUE, mut input: VALUE) -> VALUE {
    // ...
}

018.rs

// in src/lib.rs

#[no_mangle]
unsafe extern "C" fn pub_lowercase(_klass: VALUE, mut input: VALUE) -> VALUE {
    let ruby_string = cstr_to_string(rb_string_value_cstr(&mut input));
    let lowercased = ruby_string.to_lowercase();
    // ...
}

019.rs

// in src/lib.rs

#[no_mangle]
unsafe extern "C" fn pub_lowercase(_klass: VALUE, mut input: VALUE) -> VALUE {
    let ruby_string = cstr_to_string(rb_string_value_cstr(&mut input));
    let lowercased = ruby_string.to_lowercase();
    let lowercased_cstring = CString::new(lowercased).unwrap();
    let size = ruby_string.len() as c_long;

    rb_utf8_str_new(lowercased_cstring.as_ptr(), size)
}

020.rs

// in src/lib.rs

#[allow(non_snake_case)]
#[no_mangle]
pub extern "C" fn Init_rust_ruby_example() {
    let name = CString::new("RustRubyExample").unwrap();

    // ...Code for defining "RustRubyExample#reverse" omitted

    let function_name = CString::new("lowercase").unwrap();
    let callback = unsafe {
        std::mem::transmute::<
            unsafe extern "C" fn(VALUE, VALUE) -> VALUE,
            unsafe extern "C" fn() -> VALUE,
        >(pub_lowercase)
    };
    let klass = unsafe { rb_define_module(name.as_ptr()) };

    unsafe { rb_define_module_function(klass, function_name.as_ptr(), Some(callback), 1) }
}

021.sh

$ gem build rust_ruby_example.gemspec --output rust_ruby_example.gem
  // Warnings omitted
  Successfully built RubyGem
  Name: rust_ruby_example
  Version: 0.1.0
  File: rust_ruby_example.gem

$ gem install rust_ruby_example.gem
Building native extensions. This could take a while...
Successfully installed rust_ruby_example-0.1.0
1 gem installed

022.sh

$ irb
irb(main):001:0> require 'rust_ruby_example'
=> true
irb(main):002:1* RustRubyExample.lowercase("RustRubyExample")
=> "rustrubyexample"