Fixed reference types being passed to getitemint (GH-3755)

Cython/Compiler/ExprNodes.py

@@ -3739,6 +3739,8 @@ class IndexNode(_IndexingBaseNode):
         if not base_type.is_cfunction:
             self.index = self.index.analyse_types(env)
             self.original_index_type = self.index.type
+            if self.original_index_type.is_reference:
+                self.original_index_type = self.original_index_type.ref_base_type
 
             if base_type.is_unicode_char:
                 # we infer Py_UNICODE/Py_UCS4 for unicode strings in some

tests/run/lvalue_refs.pyx

@@ -28,3 +28,15 @@ def test_lvalue_ref_assignment():
 
     assert bar[0] == &baz[0][0]
     assert bar[0][0] == bongle
+
+# not *strictly* lvalue refs but this file seems the closest applicable place for it.
+# GH 3754 - std::vector operator[] returns a reference, and this causes problems if
+# the reference is passed into Cython __Pyx_GetItemInt
+def test_ref_used_for_indexing():
+    """
+    >>> test_ref_used_for_indexing()
+    'looked up correctly'
+    """
+    cdef vector[int] idx = [1,2,3]
+    d = {1: "looked up correctly", 2:"oops"}
+    return d[idx[0]]