Escape newlines in repr for assertion rewriting

The assertion formatting mini-language depends on newlines being
escaped.  Unfortunately if the repr of an object contained
newlines the rewriting module did not escape those, which is now
fixed.

Fixes issue453.

CHANGELOG

@@ -3,6 +3,9 @@ NEXT
 
 - fixed issue561: adapt autouse fixture example for python3.
 
+- fixed issue453: assertion rewriting issue with __repr__ containing
+  "\n{", "\n}" and "\n~".
+
 2.6.1
 -----------------------------------
 

_pytest/assertion/rewrite.py

@@ -326,7 +326,15 @@ def rewrite_asserts(mod):
     AssertionRewriter().run(mod)
 
 
-_saferepr = py.io.saferepr
+def _saferepr(obj):
+    repr = py.io.saferepr(obj)
+    if py.builtin._istext(repr):
+        t = py.builtin.text
+    else:
+        t = py.builtin.bytes
+    return repr.replace(t("\n"), t("\\n"))
+
+
 from _pytest.assertion.util import format_explanation as _format_explanation # noqa
 
 def _should_repr_global_name(obj):

testing/test_assertrewrite.py

@@ -313,6 +313,17 @@ class TestAssertionRewrite:
             assert "%test" == "test"
         assert getmsg(f).startswith("assert '%test' == 'test'")
 
+    def test_custom_repr(self):
+        def f():
+            class Foo(object):
+                a = 1
+
+                def __repr__(self):
+                    return "\n{ \n~ \n}"
+            f = Foo()
+            assert 0 == f.a
+        assert r"where 1 = \n{ \n~ \n}.a" in util._format_lines([getmsg(f)])[0]
+
 
 class TestRewriteOnImport: