Update type for CSV.foreach

Gemfile

@@ -30,6 +30,7 @@ gem "rbs-amber", path: "test/assets/test-gem"
 
 # Bundled gems
 gem "net-smtp"
+gem 'csv'
 
 group :minitest do
   gem "minitest"

Gemfile.lock

@@ -18,6 +18,7 @@ GEM
     ast (2.4.2)
     base64 (0.2.0)
     bigdecimal (3.1.6)
+    csv (3.2.8)
     dbm (1.1.0)
     diff-lcs (1.5.0)
     digest (3.1.1)
@@ -102,6 +103,7 @@ DEPENDENCIES
   abbrev
   base64
   bigdecimal
+  csv
   dbm
   digest
   fileutils

stdlib/csv/0/csv.rbs

@@ -1722,7 +1722,10 @@ class CSV < Object
   #     would read `UTF-32BE` data from the file but transcode it to `UTF-8`
   #     before parsing.
   #
-  def self.foreach: [U] (String | IO | StringIO path, ?::Hash[Symbol, U] options) { (::Array[String?] arg0) -> void } -> void
+  def self.foreach: (String | IO path, ?String mode, headers: true, **untyped options) { (::CSV::Row arg0) -> void } -> void
+                  | (String | IO path, ?String mode, headers: true, **untyped options) -> Enumerator[::CSV::Row, void]
+                  | (String | IO path, ?String mode, **untyped options) { (::Array[String?] arg0) -> void } -> void
+                  | (String | IO path, ?String mode, **untyped options) -> Enumerator[::Array[String?], void]
 
   # <!--
   #   rdoc-file=lib/csv.rb

test/stdlib/CSV_test.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require_relative "test_helper"
+require "csv"
+
+class CSVSingletonTest < Test::Unit::TestCase
+  include TestHelper
+
+  library 'csv'
+  testing "singleton(::CSV)"
+
+  def test_foreach
+    tmpdir = Dir.mktmpdir
+    path = File.join(tmpdir, "example.csv")
+    File.write(path, "a,b,c\n1,2,3\n")
+
+    string_array_block = ->(row) { row.size }
+    assert_send_type "(String path) { (Array[String?]) -> void } -> void",
+                     CSV, :foreach, path, &string_array_block
+    assert_send_type "(IO path) { (Array[String?]) -> void } -> void",
+                     CSV, :foreach, File.open(path), &string_array_block
+
+    csv_row_array_block = ->(row) { row.fields }
+    assert_send_type "(String path, headers: true) { (CSV::Row) -> void } -> void",
+                     CSV, :foreach, path, headers: true, &csv_row_array_block
+    assert_send_type "(String path, headers: false) { (Array[String?]) -> void } -> void",
+                     CSV, :foreach, path, headers: false, &string_array_block
+    assert_send_type "(IO path, headers: bool) { (CSV::Row) -> void } -> void",
+                     CSV, :foreach, File.open(path), headers: true, &csv_row_array_block
+
+    assert_send_type "(String path, **untyped) -> Enumerator[Array[String?], void]",
+                     CSV, :foreach, path, encoding: 'UTF-8'
+    assert_send_type "(String path, headers: bool) -> Enumerator[CSV::Row, void]",
+                     CSV, :foreach, path, headers: true
+    assert_send_type "(String path, headers: bool, **untyped) -> Enumerator[CSV::Row, void]",
+                     CSV, :foreach, path, headers: true, encoding: 'UTF-8'
+  end
+end