ARROW-6813: [Ruby] Arrow::Table.load with headers=true leads to excep…

…tion in Arrow 0.15

After reviewing the commentary on apache#5206 , and examining the new read options, I've concluded that supporting a boolean `:headers` option at this level is not a good idea.  In particular, all the interpretations of `headers: false` that I could think of would be surprising to a typical Ruby CSV programmer (does it mean `:autogenerate_column_names`? are you required to add `:column_names` instead?).

So I've just made the exception clearer.  It would be great if there were a way to pull the [documentation of the options](https://github.com/apache/arrow/blob/02d1e9736808d9a9624bef5577c880d8c165e853/python/pyarrow/_csv.pyx#L42) over from the `.py` files into the Ruby doc.

Closes apache#5609 from cobbr2/bug/ARROW-6813-ruby-headers-option-fail and squashes the following commits:

c941b10 <Rick Cobb> Retry the docker-compose build now that I see it succeed for anybody
0d67b65 <Rick Cobb> Retry the docker-compose build, can't find button in Github UX
0134d5e <Rick Cobb> simplify headers handling
2dedfad <Rick Cobb> and now with a headers: string test
7655138 <Rick Cobb> Merge work that makes headers work more like CSV
1215bfe <Rick Cobb> truthy headers should work like CSV
c7fe77f <Rick Cobb> Make `headers:` compatible with Ruby's CSV.new
a4934b6 <Rick Cobb> Should never have committed Gemfile.lock
4af0111 <Rick Cobb> Make a better error message than NoMethodError
0341652 <Rick Cobb> WIP: is this the correct test... and will skip_rows work?

Authored-by: Rick Cobb <rick@grandrounds.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>

ruby/red-arrow/lib/arrow/csv-loader.rb

@@ -93,10 +93,17 @@ def reader_options
       @options.each do |key, value|
         case key
         when :headers
-          if value
-            options.n_header_rows = 1
+          case value
+          when ::Array
+            options.column_names = value
+          when String
+            return nil
           else
-            options.n_header_rows = 0
+            if value
+              options.generate_column_names = false
+            else
+              options.generate_column_names = true
+            end
           end
         when :column_types
           value.each do |name, type|

ruby/red-arrow/test/test-csv-loader.rb

@@ -121,6 +121,81 @@ def load_csv(data, options)
       Arrow::CSVLoader.load(data, options)
     end
 
+    sub_test_case(":headers") do
+      test("true") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(value: values),
+                     load_csv(<<-CSV, headers: true))
+value
+a
+b
+c
+                     CSV
+      end
+
+      test(":first_line") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(value: values),
+                     load_csv(<<-CSV, headers: :first_line))
+value
+a
+b
+c
+                     CSV
+      end
+
+      test("truthy") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(value: values),
+                     load_csv(<<-CSV, headers: 0))
+value
+a
+b
+c
+                     CSV
+      end
+
+      test("Array of column names") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(column: values),
+                     load_csv(<<-CSV, headers: ["column"]))
+a
+b
+c
+                     CSV
+      end
+
+      test("false") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(f0: values),
+                     load_csv(<<-CSV, headers: false))
+a
+b
+c
+                     CSV
+      end
+
+      test("nil") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(f0: values),
+                     load_csv(<<-CSV, headers: nil))
+a
+b
+c
+                     CSV
+      end
+
+      test("string") do
+        values = Arrow::StringArray.new(["a", "b", "c"])
+        assert_equal(Arrow::Table.new(column: values),
+                     load_csv(<<-CSV, headers: "column"))
+a
+b
+c
+                     CSV
+      end
+    end
+
     test(":column_types") do
       assert_equal(Arrow::Table.new(:count => Arrow::UInt16Array.new([1, 2, 4])),
                    load_csv(<<-CSV, column_types: {count: :uint16}))