Add Steep for type checking

Author: sferik

.github/workflows/steep.yml

@@ -0,0 +1,17 @@
+name: steep
+
+on: [push, pull_request]
+
+jobs:
+  steep:
+    name: Type check
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v6
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ruby
+        bundler-cache: true
+    - name: Run Steep
+      run: bundle exec rake steep

Gemfile

@@ -3,5 +3,6 @@ source "https://rubygems.org"
 gemspec
 
 gem "rake"
+gem "steep"
 gem "test-unit"
 gem "test-unit-ruby-core"

Rakefile

@@ -7,4 +7,9 @@ Rake::TestTask.new(:test) do |t|
   t.test_files = FileList["test/**/test_*.rb"]
 end
 
+desc "Type check with Steep"
+task :steep do
+  sh "steep check"
+end
+
 task :default => :test

Steepfile

@@ -0,0 +1,21 @@
+target :lib do
+  check "lib"
+  signature "sig"
+
+  library "cgi"
+  library "open-uri"
+  library "openssl"
+  library "resolv"
+  library "securerandom"
+  library "socket"
+  library "strscan"
+  library "tempfile"
+  library "timeout"
+  library "uri"
+  library "zlib"
+
+  d = Steep::Diagnostic::Ruby.default.dup
+  d[Steep::Diagnostic::Ruby::ArgumentTypeMismatch] = :information
+  d[Steep::Diagnostic::Ruby::NoMethod] = :information
+  configure_code_diagnostics(d)
+end

sig/net-http.rbs

@@ -1,6 +1,14 @@
+# TCPSocket.open is an alias for TCPSocket.new in Ruby,
+# but RBS inherits IO.open which has a different signature.
+class TCPSocket
+  def self.open: (String remote_host, Integer remote_port, ?String? local_host, ?Integer? local_port, ?open_timeout: Numeric?) -> TCPSocket
+               | (String remote_host, Integer remote_port, ?String? local_host, ?Integer? local_port) -> TCPSocket
+end
+
 module Net
   # Stubs for net-protocol classes
   class Protocol
+    def self.new: (*untyped) -> instance
   end
 
   class ProtocolError < StandardError
@@ -323,8 +331,7 @@ module Net
     def initialize: (String address, ?Integer? port) -> void
     def started?: () -> bool
     alias active? started?
-    def start: () -> Net::HTTP
-             | () { (Net::HTTP http) -> untyped } -> untyped
+    def start: () ?{ (Net::HTTP http) -> untyped } -> (Net::HTTP | untyped)
     def finish: () -> void
 
     def use_ssl?: () -> bool