Make temp attribute more solid and add unit test on regression

Signed-off-by: Julien Danjou <julien@danjou.info>

hy/compiler.py

@@ -66,7 +66,7 @@ class HyTypeError(TypeError):
         self.expression = expression
 
     def __str__(self):
-        return (self.message + " (line %s, column %d)"
+        return (super(HyTypeError, self).__str__() + " (line %s, column %d)"
                 % (self.expression.start_line,
                    self.expression.start_column))
 

hy/util.py

@@ -34,8 +34,10 @@ def temporary_attribute_value(obj, attribute, value):
     """Temporarily switch an object attribute value to another value."""
     original_value = getattr(obj, attribute)
     setattr(obj, attribute, value)
-    yield
-    setattr(obj, attribute, original_value)
+    try:
+        yield
+    finally:
+        setattr(obj, attribute, original_value)
 
 
 def flatten_literal_list(entry):

tests/compilers/test_ast.py

@@ -391,3 +391,14 @@ def test_ast_unicode_strings():
     assert _compile_string("test") == "test"
     assert _compile_string("\u03b1\u03b2") == "\u03b1\u03b2"
     assert _compile_string("\xc3\xa9") == "\xc3\xa9"
+
+
+def test_compile_error():
+    """Ensure we get compile error in tricky cases"""
+    try:
+        hy_compile(tokenize("(fn [] (= 1))"))
+    except HyCompileError as e:
+        assert(str(e)
+               == "`=' needs at least 2 arguments, got 1 (line 1, column 8)")
+    else:
+        assert(False)