Fix a crash when tokenizing a single quote

NEWS

@@ -23,6 +23,7 @@ Changes from 0.12.1
    * `setv` no longer unnecessarily tries to get attributes
    * `loop` no longer replaces string literals equal to "recur"
    * The REPL now prints the correct value of `do` and `try` forms
+   * Fixed a crash when tokenizing a single quote followed by whitespace
 
    [ Misc. Improvements ]
    * New contrib module `hy-repr`

hy/lex/__init__.py

@@ -34,7 +34,7 @@ def tokenize(buf):
     except LexingError as e:
         pos = e.getsourcepos()
         raise LexException("Could not identify the next token.",
-                           pos.lineno, pos.colno)
+                           pos.lineno, pos.colno, buf)
     except LexException as e:
         if e.source is None:
             e.source = buf

hy/lex/exceptions.py

@@ -24,12 +24,12 @@ from hy.errors import HyError
 
 class LexException(HyError):
     """Error during the Lexing of a Hython expression."""
-    def __init__(self, message, lineno, colno):
+    def __init__(self, message, lineno, colno, source=None):
         super(LexException, self).__init__(message)
         self.message = message
         self.lineno = lineno
         self.colno = colno
-        self.source = None
+        self.source = source
         self.filename = '<stdin>'
 
     def __str__(self):

tests/test_lex.py

@@ -63,6 +63,17 @@ def test_unbalanced_exception():
         pass
 
 
+def test_lex_single_quote_err():
+    "Ensure tokenizing \"' \" throws a LexException that can be stringified"
+    # https://github.com/hylang/hy/issues/1252
+    try:
+        tokenize("' ")
+    except LexException as e:
+        assert "Could not identify the next token" in str(e)
+    else:
+        assert False
+
+
 def test_lex_expression_symbols():
     """ Make sure that expressions produce symbols """
     objs = tokenize("(foo bar)")