fix recursion within import hook and source.decode in particular

_pytest/assertion/rewrite.py

@@ -215,11 +215,17 @@ def _rewrite_test(state, fn):
         if (not source.startswith(BOM_UTF8) and
             (not cookie_re.match(source[0:end1]) or
             not cookie_re.match(source[end1:end2]))):
+            if hasattr(state, "_indecode"):
+                return None  # encodings imported us again, we don't rewrite
+            state._indecode = True
+            try:
                 try:
                     source.decode("ascii")
                 except UnicodeDecodeError:
                     # Let it fail in real import.
                     return None
+            finally:
+                del state._indecode
     # On Python versions which are not 2.7 and less than or equal to 3.1, the
     # parser expects *nix newlines.
     if REWRITE_NEWLINES:

testing/test_assertion.py

@@ -320,3 +320,17 @@ def test_warn_missing(testdir):
     result.stderr.fnmatch_lines([
         "*WARNING*assert statements are not executed*",
     ])
+
+def test_recursion_source_decode(testdir):
+    testdir.makepyfile("""
+        def test_something():
+            pass
+    """)
+    testdir.makeini("""
+        [pytest]
+        python_files = *.py
+    """)
+    result = testdir.runpytest("--collectonly")
+    result.stdout.fnmatch_lines("""
+        <Module*>
+    """)