From 7dd67a6193695f9def1ac2384d9ab0f71ea44c8b Mon Sep 17 00:00:00 2001
From: Uiri <uiri00@gmail.com>
Date: Sat, 27 Oct 2018 00:35:14 -0400
Subject: [PATCH] Fix #217: dumps unable to detect circular refs

If an object is passed to dumps, and that object has a circular
reference, then dumps will raise a ValueError because an object with
circular references cannot be encoded as valid TOML.
---
 tests/test_api.py | 13 +++++++++++++
 toml/encoder.py   |  6 ++++++
 2 files changed, 19 insertions(+)

diff --git a/tests/test_api.py b/tests/test_api.py
index 5f94778..f14057a 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -51,6 +51,19 @@ def test_valid_tests():
         toml.dumps(toml.load(open(os.path.join(valid_dir, f))))
 
 
+def test_circular_ref():
+    a = {}
+    b = {}
+    b['c'] = 4
+    b['self'] = b
+    a['b'] = b
+    with pytest.raises(ValueError):
+        toml.dumps(a)
+
+    with pytest.raises(ValueError):
+        toml.dumps(b)
+
+
 def test__dict():
     class TestDict(dict):
         pass
diff --git a/toml/encoder.py b/toml/encoder.py
index 79bfd37..4b54afa 100644
--- a/toml/encoder.py
+++ b/toml/encoder.py
@@ -46,7 +46,13 @@ def dumps(o, encoder=None):
         encoder = TomlEncoder(o.__class__)
     addtoretval, sections = encoder.dump_sections(o, "")
     retval += addtoretval
+    outer_objs = [id(o)]
     while sections:
+        section_ids = [id(section) for section in sections]
+        for outer_obj in outer_objs:
+            if outer_obj in section_ids:
+                raise ValueError("Circular reference detected")
+        outer_objs += section_ids
         newsections = encoder.get_empty_table()
         for section in sections:
             addtoretval, addtosections = encoder.dump_sections(