X allow coercion only from the same component types

Cython/Compiler/PyrexTypes.py

@@ -4063,10 +4063,16 @@ class CTupleType(CType):
         return True
 
     def assignable_from_resolved_type(self, src_type):
-        if src_type.is_cpp_class and src_type.cname == "std::pair" and len(src_type.templates) == 2:
-            # XXX len self.xxx == len src_type.templates
-            # XXX types are assignable
+        # (X,Y) can be assigned from std::pair[X,Y]
+        if src_type.is_cpp_class and src_type.cname == "std::pair":
+            if not (len(self.components) == len(src_type.templates) == 2):
+                return False
+            for (c_dst, c_src) in zip(self.components, src_type.templates):
+                if not c_dst.same_as(c_src):
+                    return False
+            return True
 
+            """
             print
             #from Cython.Compiler.Pipeline import dumptree
             #dumptree(src_type)
@@ -4075,7 +4081,8 @@ class CTupleType(CType):
             print src_type.cname
             print src_type.templates
             print
-            return 1    # XXX check types match
+            return 1    # XXX check types are the same
+            """
 
         return super(CTupleType, self).assignable_from_resolved_type(src_type)
 

tests/errors/e_cpp_ctuple.pyx

+# tag: cpp
+# mode: error
+
+from libcpp.utility cimport pair
+
+cdef void f(pair[int,double] pxy) nogil:
+    cdef int x = pxy
+    cdef (int, double, int) xyz = pxy
+
+    # NOTE the following is also error, simplary to how (int, int) cannot be assigned from (int, double)
+    cdef (int, int) ixy = pxy
+
+
+_ERRORS = u"""
+7:17: Cannot assign type 'pair[int,double]' to 'int'
+8:34: Cannot assign type 'pair[int,double]' to '(int, double, int)'
+11:26: Cannot assign type 'pair[int,double]' to '(int, int)'
+"""