Allow comments on the last line of the query (fixes #39)

Author: Cito

README.md

@@ -13,7 +13,7 @@ a query language for APIs created by Facebook.
 [![Code Style](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/ambv/black)
 
 The current version 1.1.0b0 of GraphQL-core-next is up-to-date with GraphQL.js version
-14.4.0. All parts of the API are covered by an extensive test suite of currently 1881
+14.4.0. All parts of the API are covered by an extensive test suite of currently 1882
 unit tests.
 
 

graphql/language/lexer.py

@@ -169,7 +169,7 @@ def read_comment(self, start: int, line: int, col: int, prev: Token) -> Token:
         position = start
         while True:
             position += 1
-            if position > body_length:
+            if position >= body_length:
                 break
             char = body[position]
             if char < " " and char != "\t":

tests/language/test_parser.py

@@ -389,6 +389,25 @@ def contains_references_to_start_and_end_tokens():
         assert isinstance(end_token, Token)
         assert end_token.kind == TokenKind.EOF
 
+    def allows_comments_everywhere_in_the_source():
+        # make sure first and last line can be comment
+        result = parse(
+            """# top comment
+            {
+              field # field comment
+            }
+            # bottom comment"""
+        )
+        top_comment = result.loc.start_token.next
+        assert top_comment.kind is TokenKind.COMMENT
+        assert top_comment.value == " top comment"
+        field_comment = top_comment.next.next.next
+        assert field_comment.kind is TokenKind.COMMENT
+        assert field_comment.value == " field comment"
+        bottom_comment = field_comment.next.next
+        assert bottom_comment.kind is TokenKind.COMMENT
+        assert bottom_comment.value == " bottom comment"
+
 
 def describe_parse_value():
     def parses_null_value():