Fix a token incompatibility for Prism::Translation::Parser::Lexer

This PR fixes a token incompatibility between Parser gem and `Prism::Translation::Parser`
for the heredocs_leading_whitespace.txt test.

Author: koic

lib/prism/translation/parser/lexer.rb

@@ -217,6 +217,8 @@ def to_a
           index = 0
           length = lexed.length
 
+          heredoc_identifier_stack = []
+
           while index < length
             token, state = lexed[index]
             index += 1
@@ -275,6 +277,9 @@ def to_a
             when :tSPACE
               value = nil
             when :tSTRING_BEG
+              if token.type == :HEREDOC_START
+                heredoc_identifier_stack.push(value.match(/<<[-~]?["']?(?<heredoc_identifier>.*?)["']?\z/)[:heredoc_identifier])
+              end
               if ["\"", "'"].include?(value) && (next_token = lexed[index][0]) && next_token.type == :STRING_END
                 next_location = token.location.join(next_token.location)
                 type = :tSTRING
@@ -322,7 +327,7 @@ def to_a
             when :tSTRING_END
               if token.type == :HEREDOC_END && value.end_with?("\n")
                 newline_length = value.end_with?("\r\n") ? 2 : 1
-                value = value.sub(/\r?\n\z/, '')
+                value = heredoc_identifier_stack.pop
                 location = Range.new(source_buffer, offset_cache[token.location.start_offset], offset_cache[token.location.end_offset - newline_length])
               elsif token.type == :REGEXP_END
                 value = value[0]

test/prism/fixtures/heredocs_leading_whitespace.txt

@@ -3,6 +3,11 @@ a
 b
      FOO
 
+<<-"  FOO"
+a
+b
+     FOO
+
 <<-'  FOO'
 a
 b

test/prism/parser_test.rb

@@ -73,7 +73,6 @@ class ParserTest < TestCase
     skip_tokens = [
       "comments.txt",
       "heredoc_with_comment.txt",
-      "heredocs_leading_whitespace.txt",
       "indented_file_end.txt",
       "strings.txt",
       "xstring_with_backslash.txt"