implement independent coercion of subexpressions for conditional if-else expression

Cython/Compiler/ExprNodes.py

@@ -9650,8 +9650,9 @@ class CondExprNode(ExprNode):
         return self.true_val.type_dependencies(env) + self.false_val.type_dependencies(env)
 
     def infer_type(self, env):
-        return PyrexTypes.independent_spanning_type(self.true_val.infer_type(env),
-                                                    self.false_val.infer_type(env))
+        return PyrexTypes.independent_spanning_type(
+            self.true_val.infer_type(env),
+            self.false_val.infer_type(env))
 
     def calculate_constant_result(self):
         if self.test.constant_result:
@@ -9663,17 +9664,27 @@ class CondExprNode(ExprNode):
         self.test = self.test.analyse_types(env).coerce_to_boolean(env)
         self.true_val = self.true_val.analyse_types(env)
         self.false_val = self.false_val.analyse_types(env)
-        self.type = PyrexTypes.independent_spanning_type(self.true_val.type, self.false_val.type)
+        self.is_temp = 1
+        return self.analyse_result_type(env)
+
+    def analyse_result_type(self, env):
+        self.type = PyrexTypes.independent_spanning_type(
+            self.true_val.type, self.false_val.type)
         if self.type.is_pyobject:
             self.result_ctype = py_object_type
         if self.true_val.type.is_pyobject or self.false_val.type.is_pyobject:
             self.true_val = self.true_val.coerce_to(self.type, env)
             self.false_val = self.false_val.coerce_to(self.type, env)
-        self.is_temp = 1
         if self.type == PyrexTypes.error_type:
             self.type_error()
         return self
 
+    def coerce_to(self, dst_type, env):
+        self.true_val = self.true_val.coerce_to(dst_type, env)
+        self.false_val = self.false_val.coerce_to(dst_type, env)
+        self.result_ctype = None
+        return self.analyse_result_type(env)
+
     def type_error(self):
         if not (self.true_val.type.is_error or self.false_val.type.is_error):
             error(self.pos, "Incompatible types in conditional expression (%s; %s)" %

tests/run/if_else_expr.pyx

@@ -31,3 +31,14 @@ def test_cpp_pyobject_cast(Foo obj1, Foo obj2, cond):
     (<Foo>, None)
     """
     return func(obj1 if cond else obj2, obj1.data if cond else obj2.data)
+
+
+def test_charptr_coercion(x):
+    """
+    >>> print(test_charptr_coercion(True))
+    abc
+    >>> print(test_charptr_coercion(False))
+    def
+    """
+    cdef char* s = 'abc' if x else 'def'
+    return s.decode('ascii')