Fix conversion from DictNode to std::map (GH-4231)

Reported in https://github.com/cython/cython/pull/4228

Cython/Compiler/ExprNodes.py

@@ -8871,8 +8871,7 @@ class DictNode(ExprNode):
                             value = value.arg
                         item.value = value.coerce_to(member.type, env)
         else:
-            self.type = error_type
-            error(self.pos, "Cannot interpret dict as type '%s'" % dst_type)
+            return super(DictNode, self).coerce_to(dst_type, env)
         return self
 
     def release_errors(self):

tests/errors/reversed_literal_pyobjs.pyx

@@ -10,6 +10,7 @@ for i in reversed(range(j, [], 2)):
     pass
 for i in reversed(range(j, [], -2)):
     pass
+# code below is no longer a compile-time error (although won't run without an exception)
 for i in reversed(range({}, j, 2)):
     pass
 for i in reversed(range({}, j, -2)):
@@ -24,8 +25,4 @@ _ERRORS = """
 7:24: Cannot coerce list to type 'long'
 9:27: Cannot coerce list to type 'long'
 11:27: Cannot coerce list to type 'long'
-13:24: Cannot interpret dict as type 'long'
-15:24: Cannot interpret dict as type 'long'
-17:27: Cannot interpret dict as type 'long'
-19:27: Cannot interpret dict as type 'long'
 """

tests/run/cpp_stl_conversion.pyx

@@ -97,6 +97,23 @@ def test_int_vector(o):
     cdef vector[int] v = o
     return v
 
+cdef vector[int] takes_vector(vector[int] x):
+    return x
+
+def test_list_literal_to_vector():
+    """
+    >>> test_list_literal_to_vector()
+    [1, 2, 3]
+    """
+    return takes_vector([1, 2, 3])
+
+def test_tuple_literal_to_vector():
+    """
+    >>> test_tuple_literal_to_vector()
+    [1, 2, 3]
+    """
+    return takes_vector((1, 2, 3))
+
 def test_string_vector(s):
     """
     >>> list(map(normalize, test_string_vector('ab cd ef gh'.encode('ascii'))))
@@ -241,3 +258,14 @@ def test_enum_map(o):
     """
     cdef map[Color, Color] m = o
     return m
+
+cdef map[unsigned int, unsigned int] takes_map(map[unsigned int, unsigned int] m):
+    return m
+
+def test_dict_literal_to_map():
+    """
+    >>> test_dict_literal_to_map()
+    {1: 1}
+    """
+    return takes_map({1: 1})  # https://github.com/cython/cython/pull/4228
+                              # DictNode could not be converted directly