Reference type inference

Cython/Compiler/TypeInference.py

@@ -276,10 +276,14 @@ def find_spanning_type(type1, type2):
 
 def aggressive_spanning_type(types, might_overflow):
     result_type = reduce(find_spanning_type, types)
+    if result_type.is_reference:
+        result_type = result_type.ref_base_type
     return result_type
 
 def safe_spanning_type(types, might_overflow):
     result_type = reduce(find_spanning_type, types)
+    if result_type.is_reference:
+        result_type = result_type.ref_base_type
     if result_type.is_pyobject:
         # any specific Python type is always safe to infer
         return result_type

tests/wrappers/cpp_references.pyx

+cimport cython
+
+
 cdef extern from "cpp_references_helper.h":
     cdef int& ref_func(int&)
     
     cdef int ref_var_value
     cdef int& ref_var
 
+
 def test_ref_func(int x):
     """
     >>> test_ref_func(2)
@@ -42,3 +46,15 @@ def test_ref_assign(int x):
     """
     cdef double d = ref_func(x)
     return d
+
+@cython.infer_types(True)
+def test_ref_inference(int x):
+    """
+    >>> test_ref_inference(23)
+    23
+    >>> test_ref_inference(29)
+    29
+    """
+    z = ref_func(x)
+    assert cython.typeof(z) == "int", cython.typeof(z)
+    return z