Give an error on empty attributes (#1138)

Give an error on empty attributes

closes #1137

hy/compiler.py

@@ -2588,6 +2588,19 @@ class HyASTCompiler(object):
     def compile_symbol(self, symbol):
         if "." in symbol:
             glob, local = symbol.rsplit(".", 1)
+
+            if not glob:
+                raise HyTypeError(symbol, 'cannot access attribute on '
+                                          'anything other than a name '
+                                          '(in order to get attributes of'
+                                          'expressions, use '
+                                          '`(. <expression> {attr})` or '
+                                          '`(.{attr} <expression>)`)'.format(
+                                              attr=local))
+
+            if not local:
+                raise HyTypeError(symbol, 'cannot access empty attribute')
+
             glob = HySymbol(glob).replace(symbol)
             ret = self.compile_symbol(glob)
 

tests/compilers/test_ast.py

@@ -542,6 +542,15 @@ def test_attribute_access():
     cant_compile("(. foo bar baz [0] quux {frob})")
 
 
+def test_attribute_empty():
+    """Ensure using dot notation with a non-expression is an error"""
+    cant_compile(".")
+    cant_compile("foo.")
+    cant_compile(".foo")
+    cant_compile('"bar".foo')
+    cant_compile('[2].foo')
+
+
 def test_cons_correct():
     """Ensure cons gets compiled correctly"""
     can_compile("(cons a b)")