Support itblock for Prism::Translation::Parser

## Summary

`itblock` node is added to support the `it` block parameter syntax introduced in Ruby 3.4.

```console
$ ruby -Ilib -rprism -rprism/translation/parser34 -e 'buffer = Parser::Source::Buffer.new("path"); buffer.source = "proc { it }"; \
                                                      p Prism::Translation::Parser34.new.tokenize(buffer)[0]'
s(:itblock,
  s(:send, nil, :proc), :it,
  s(:lvar, :it))
```

This node design is similar to the `numblock` node, which was introduced for the numbered parameter syntax in Ruby 2.7.

```
$ ruby -Ilib -rprism -rprism/translation/parser34 -e 'buffer = Parser::Source::Buffer.new("path"); buffer.source = "proc { _1 }"; \
                                                      p Prism::Translation::Parser34.new.tokenize(buffer)[0]'
s(:numblock,
  s(:send, nil, :proc), 1,
  s(:lvar, :_1))
```

The difference is that while numbered parameters can have multiple parameters, the `it` block parameter syntax allows only a single parameter.

In Ruby 3.3, the conventional node prior to the `it` block parameter syntax is returned.

```console
$ ruby -Ilib -rprism -rprism/translation/parser33 -e 'buffer = Parser::Source::Buffer.new("path"); buffer.source = "proc { it }"; \
                                                      p Prism::Translation::Parser33.new.tokenize(buffer)[0]'
s(:block,
  s(:send, nil, :proc),
  s(:args),
  s(:send, nil, :it))
```

## Development Note

The Parser gem does not yet support the `it` block parameter syntax. This is the first case where Prism's node design precedes that of the Parser gem.
When implementing whitequark/parser#962, this node design will need to be taken into consideration.

lib/prism/translation/parser/builder.rb

@@ -6,7 +6,55 @@ class Parser
       # A builder that knows how to convert more modern Ruby syntax
       # into whitequark/parser gem's syntax tree.
       class Builder < ::Parser::Builders::Default
+        # It represents the `it` block argument, which is not yet implemented in the Parser gem.
+        def itarg
+          n(:itarg, [:it], nil)
+        end
 
+        # The following three lines have been added to support the `it` block parameter syntax in the source code below.
+        #
+        #   if args.type == :itarg
+        #     block_type = :itblock
+        #     args = :it
+        #
+        # https://github.com/whitequark/parser/blob/v3.3.7.1/lib/parser/builders/default.rb#L1122-L1155
+        def block(method_call, begin_t, args, body, end_t)
+          _receiver, _selector, *call_args = *method_call
+
+          if method_call.type == :yield
+            diagnostic :error, :block_given_to_yield, nil, method_call.loc.keyword, [loc(begin_t)]
+          end
+
+          last_arg = call_args.last
+          if last_arg && (last_arg.type == :block_pass || last_arg.type == :forwarded_args)
+            diagnostic :error, :block_and_blockarg, nil, last_arg.loc.expression, [loc(begin_t)]
+          end
+
+          if args.type == :itarg
+            block_type = :itblock
+            args = :it
+          elsif args.type == :numargs
+            block_type = :numblock
+            args = args.children[0]
+          else
+            block_type = :block
+          end
+
+          if [:send, :csend, :index, :super, :zsuper, :lambda].include?(method_call.type)
+            n(block_type, [ method_call, args, body ],
+              block_map(method_call.loc.expression, begin_t, end_t))
+          else
+            # Code like "return foo 1 do end" is reduced in a weird sequence.
+            # Here, method_call is actually (return).
+            actual_send, = *method_call
+            block =
+              n(block_type, [ actual_send, args, body ],
+                block_map(actual_send.loc.expression, begin_t, end_t))
+
+            n(method_call.type, [ block ],
+              method_call.loc.with_expression(join_exprs(method_call, block)))
+          end
+        end
       end
     end
   end

lib/prism/translation/parser/compiler.rb

@@ -1157,7 +1157,7 @@ def visit_it_local_variable_read_node(node)
         # -> { it }
         # ^^^^^^^^^
         def visit_it_parameters_node(node)
-          builder.args(nil, [], nil, false)
+          builder.itarg
         end
 
         # foo(bar: baz)

test/prism/fixtures/whitequark/it_arg_after_34.txt

@@ -0,0 +1,7 @@
+-> do it + 42 end
+
+-> { it + 42 }
+
+m do it + 42 end
+
+m { it + 42 }

test/prism/ruby/parser_test.rb

@@ -6,6 +6,8 @@
   verbose, $VERBOSE = $VERBOSE, nil
   require "parser/ruby33"
   require "prism/translation/parser33"
+  require "parser/ruby34"
+  require "prism/translation/parser34"
 rescue LoadError
   # In CRuby's CI, we're not going to test against the parser gem because we
   # don't want to have to install it. So in this case we'll just skip this test.
@@ -55,6 +57,12 @@ def ==(other)
 
 module Prism
   class ParserTest < TestCase
+    IT_BLOCK_PARAMETER_FIXTURES = [
+      'whitequark/it_arg_after_34.txt'
+    ]
+
+    RUBY34_FIXTURES = IT_BLOCK_PARAMETER_FIXTURES
+
     # These files contain code that is being parsed incorrectly by the parser
     # gem, and therefore we don't want to compare against our translation.
     skip_incorrect = [
@@ -86,6 +94,10 @@ class ParserTest < TestCase
       # Regex with \c escape
       "unescaping.txt",
       "seattlerb/regexp_esc_C_slash.txt",
+
+      # Please remove this once the Parser gem supports the `it` block parameter syntax:
+      # https://github.com/whitequark/parser/issues/962
+      "whitequark/it_arg_after_34.txt"
     ]
 
     # These files are either failing to parse or failing to translate, so we'll
@@ -150,7 +162,13 @@ def assert_equal_parses(fixture, compare_asts: true, compare_tokens: true, compa
       buffer = Parser::Source::Buffer.new(fixture.path, 1)
       buffer.source = fixture.read
 
-      parser = Parser::Ruby33.new
+      whitequark_parser, translation_parser = if RUBY34_FIXTURES.include?(fixture.path)
+        [Parser::Ruby34, Prism::Translation::Parser34]
+      else
+        [Parser::Ruby33, Prism::Translation::Parser33]
+      end
+
+      parser = whitequark_parser.new
       parser.diagnostics.consumer = ->(*) {}
       parser.diagnostics.all_errors_are_fatal = true
 
@@ -161,8 +179,7 @@ def assert_equal_parses(fixture, compare_asts: true, compare_tokens: true, compa
           return
         end
 
-      actual_ast, actual_comments, actual_tokens =
-        ignore_warnings { Prism::Translation::Parser33.new.tokenize(buffer) }
+      actual_ast, actual_comments, actual_tokens = ignore_warnings { translation_parser.new.tokenize(buffer) }
 
       if expected_ast == actual_ast
         if !compare_asts && !Fixture.custom_base_path?
@@ -183,6 +200,8 @@ def assert_equal_parses(fixture, compare_asts: true, compare_tokens: true, compa
       elsif compare_asts
         assert_equal expected_ast, actual_ast, -> { assert_equal_asts_message(expected_ast, actual_ast) }
       end
+
+      assert_prism_only_node(fixture.path, actual_ast)
     end
 
     def assert_equal_asts_message(expected_ast, actual_ast)
@@ -242,5 +261,11 @@ def assert_equal_comments(expected_comments, actual_comments)
         "actual: #{actual_comments.inspect}"
       }
     end
+
+    def assert_prism_only_node(actual_ast, fixture_path)
+      if IT_BLOCK_PARAMETER_FIXTURES.include?(fixture_path)
+        assert_equal :itblock, actual_ast.children.first.type
+      end
+    end
   end
 end

test/prism/ruby/ruby_parser_test.rb

@@ -45,7 +45,11 @@ class RubyParserTest < TestCase
       "whitequark/pattern_matching_single_match.txt",
       "whitequark/ruby_bug_12402.txt",
       "whitequark/ruby_bug_14690.txt",
-      "whitequark/space_args_block.txt"
+      "whitequark/space_args_block.txt",
+
+      # Please remove this once the Parser gem supports the `it` block parameter syntax:
+      # https://github.com/whitequark/parser/issues/962
+      "whitequark/it_arg_after_34.txt"
     ]
 
     # https://github.com/seattlerb/ruby_parser/issues/344