Merge pull request #2012 from euglena1215/csv-headers

stdlib: Add types for CSV#headers

stdlib/csv/0/csv.rbs

@@ -2196,6 +2196,16 @@ class CSV < Object
   #
   def each: () -> Enumerator[untyped, Integer]
           | () { (untyped) -> void } -> Integer
+
+  # <!--
+  #   rdoc-file=lib/csv.rb
+  #   - csv.headers -> object
+  # -->
+  # Returns the value that determines whether headers are used; used for parsing;
+  # see {Option `headers`[}](#class-CSV-label-Option+headers):
+  #     CSV.new('').headers # => nil
+  #
+  def headers: () -> (Array[String] | true | nil)
 end
 
 # <!-- rdoc-file=lib/csv.rb -->

test/stdlib/CSV_test.rb

@@ -76,3 +76,23 @@ def test_read
                      CSV, :read, File.open(path)
   end
 end
+
+class CSVTest < Test::Unit::TestCase
+  include TestHelper
+
+  library "csv"
+  testing "CSV"
+
+  def test_headers
+    csv = CSV.new("header1,header2\nrow1_1,row1_2")
+    assert_send_type "() -> nil",
+                     csv, :headers
+
+    csv = CSV.new("header1,header2\nrow1_1,row1_2", headers: true)
+    assert_send_type "() -> true",
+                     csv, :headers
+    csv.read
+    assert_send_type "() -> Array[String]",
+                     csv, :headers
+  end
+end