feat: add RBS type signatures with Steep type checking

.github/workflows/main.yml

@@ -4,6 +4,9 @@ on:
   - push
   - pull_request
 
+permissions:
+  contents: read
+
 jobs:
   rspec:
     runs-on: ${{ matrix.os }}
@@ -64,6 +67,17 @@ jobs:
       - run: bundle install
       - name: Cucumber
         run: bundle exec cucumber
+  steep:
+    runs-on: ubuntu-latest
+    name: Type Check
+    steps:
+      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: "3.4.9"
+      - run: bundle install
+      - run: bundle exec rbs collection install
+      - run: bundle exec steep check
   security:
     runs-on: ubuntu-latest
     name: Security Audit
@@ -79,7 +93,7 @@ jobs:
   status:
     name: CI Status
     runs-on: ubuntu-latest
-    needs: [rspec, standard, cucumber, security]
+    needs: [rspec, standard, cucumber, security, steep]
     if: always()
     steps:
       - name: Successful CI

.gitignore

@@ -17,3 +17,6 @@ Gemfile.lock
 
 # Claude plans
 docs/plans/
+
+# RBS collection cache
+.gem_rbs_collection/

CLAUDE.md

@@ -8,11 +8,13 @@ This is the official OpenFeature SDK for Ruby — an implementation of the [Open
 
 ## Commands
 
+- **Install dependencies:** `bundle install`
 - **Run all tests:** `bundle exec rspec`
 - **Run a single test file:** `bundle exec rspec spec/open_feature/sdk/client_spec.rb`
 - **Run a specific test by line:** `bundle exec rspec spec/open_feature/sdk/client_spec.rb:43`
 - **Lint:** `bundle exec standardrb`
 - **Lint with autofix:** `bundle exec standardrb --fix`
+- **Type check:** `bundle exec steep check`
 - **Default rake (tests + lint):** `bundle exec rake`
 
 Note: Linting uses [Standard Ruby](https://github.com/standardrb/standard) (configured via the `standard` gem), which enforces double-quoted strings and its own opinionated style. There is no `.rubocop.yml` — Standard manages RuboCop configuration internally. Do not use `bundle exec rubocop` directly as a stale RuboCop server may apply different rules; always use `bundle exec standardrb`.
@@ -47,5 +49,6 @@ Providers can be registered for specific domains. `Configuration#provider(domain
 
 - All `.rb` files must have `# frozen_string_literal: true` as the first line.
 - Tests live under `spec/` and mirror the `lib/` structure. `spec/specification/` contains tests mapped to OpenFeature spec requirements.
+- RBS type signatures live under `sig/` and mirror the `lib/` structure. When changing any file under `lib/`, always update the corresponding `.rbs` file under `sig/` to reflect the new or modified method signatures, constants, or class structure. Run `bundle exec steep check` to verify type correctness after changes.
 - Always sign git commits using the `-S` flag.
 - Always include DCO sign-off in commits using the `-s` flag (i.e., `git commit -s -S`). This adds a `Signed-off-by` trailer required by the project's CI.

Gemfile

@@ -14,6 +14,7 @@ group :development, :test do
   gem "standard-performance"
   gem "simplecov", "~> 0.22.0"
   gem "simplecov-cobertura", "~> 3.0"
+  gem "steep", "~> 1.9"
   gem "timecop", "~> 0.9.10"
 end
 

Gemfile.lock

@@ -6,10 +6,26 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    activesupport (8.1.2)
+      base64
+      bigdecimal
+      concurrent-ruby (~> 1.0, >= 1.3.1)
+      connection_pool (>= 2.2.5)
+      drb
+      i18n (>= 1.6, < 2)
+      json
+      logger (>= 1.4.2)
+      minitest (>= 5.1)
+      securerandom (>= 0.3)
+      tzinfo (~> 2.0, >= 2.0.5)
+      uri (>= 0.13.1)
     ast (2.4.3)
     base64 (0.3.0)
     bigdecimal (4.0.1)
     builder (3.3.0)
+    concurrent-ruby (1.3.6)
+    connection_pool (3.0.2)
+    csv (3.3.5)
     cucumber (10.2.0)
       base64 (~> 0.2)
       builder (~> 3.2)
@@ -41,8 +57,12 @@ GEM
       reline (>= 0.3.8)
     diff-lcs (1.6.2)
     docile (1.4.1)
+    drb (2.2.3)
     erb (6.0.2)
     ffi (1.17.3)
+    fileutils (1.8.0)
+    i18n (1.14.8)
+      concurrent-ruby (~> 1.0)
     io-console (0.8.2)
     irb (1.17.0)
       pp (>= 0.6.0)
@@ -52,11 +72,19 @@ GEM
     json (2.18.1)
     language_server-protocol (3.17.0.5)
     lint_roller (1.1.0)
+    listen (3.10.0)
+      logger
+      rb-fsevent (~> 0.10, >= 0.10.3)
+      rb-inotify (~> 0.9, >= 0.9.10)
     logger (1.7.0)
     markly (0.15.2)
     memoist3 (1.0.0)
     mini_mime (1.1.5)
+    minitest (6.0.2)
+      drb (~> 2.0)
+      prism (~> 1.5)
     multi_test (1.1.0)
+    mutex_m (0.3.0)
     parallel (1.27.0)
     parser (3.3.10.2)
       ast (~> 2.4.1)
@@ -71,6 +99,12 @@ GEM
     racc (1.8.1)
     rainbow (3.1.1)
     rake (13.3.1)
+    rb-fsevent (0.11.2)
+    rb-inotify (0.11.1)
+      ffi (~> 1.0)
+    rbs (3.10.3)
+      logger
+      tsort
     rdoc (7.2.0)
       erb
       psych (>= 4.0.0)
@@ -111,6 +145,7 @@ GEM
       rubocop (>= 1.75.0, < 2.0)
       rubocop-ast (>= 1.47.1, < 2.0)
     ruby-progressbar (1.13.0)
+    securerandom (0.4.1)
     simplecov (0.22.0)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
@@ -132,15 +167,38 @@ GEM
     standard-performance (1.9.0)
       lint_roller (~> 1.1)
       rubocop-performance (~> 1.26.0)
+    steep (1.10.0)
+      activesupport (>= 5.1)
+      concurrent-ruby (>= 1.1.10)
+      csv (>= 3.0.9)
+      fileutils (>= 1.1.0)
+      json (>= 2.1.0)
+      language_server-protocol (>= 3.17.0.4, < 4.0)
+      listen (~> 3.0)
+      logger (>= 1.3.0)
+      mutex_m (>= 0.3.0)
+      parser (>= 3.1)
+      rainbow (>= 2.2.2, < 4.0)
+      rbs (~> 3.9)
+      securerandom (>= 0.1)
+      strscan (>= 1.0.0)
+      terminal-table (>= 2, < 5)
+      uri (>= 0.12.0)
     stringio (3.2.0)
+    strscan (3.1.7)
     sys-uname (1.5.0)
       ffi (~> 1.1)
       memoist3 (~> 1.0.0)
+    terminal-table (4.0.0)
+      unicode-display_width (>= 1.1.1, < 4)
     timecop (0.9.10)
     tsort (0.2.0)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
     unicode-display_width (3.2.0)
       unicode-emoji (~> 4.1)
     unicode-emoji (4.2.0)
+    uri (1.1.1)
 
 PLATFORMS
   arm64-darwin-21
@@ -167,6 +225,7 @@ DEPENDENCIES
   simplecov-cobertura (~> 3.0)
   standard
   standard-performance
+  steep (~> 1.9)
   timecop (~> 0.9.10)
 
 BUNDLED WITH

Rakefile

@@ -19,4 +19,11 @@ task :cucumber do
   sh "bundle exec cucumber"
 end
 
+begin
+  require "steep/rake_task"
+  Steep::RakeTask.new
+rescue LoadError
+  # Steep not available
+end
+
 task default: %i[spec standard]

Steepfile

@@ -0,0 +1,7 @@
+D = Steep::Diagnostic
+
+target :lib do
+  signature "sig"
+  check "lib"
+  configure_code_diagnostics(D::Ruby.lenient)
+end