MAINT: changes from review

CHANGES.rst

@@ -117,8 +117,10 @@ Other changes
 
 * The search order for include files was changed. Previously it was
   ``include_directories``, ``Cython/Includes``, ``sys.path``. Now it is
-  ``include_directories``, ``sys.path``, ``Cython/Includes``. (Github issue
-  #2905)
+  ``include_directories``, ``sys.path``, ``Cython/Includes``. This was done to
+  allow third-party ``*.pxd`` files to override the ones in Cython.
+  (Github issue #2905)
+
 
 0.29.7 (2019-0?-??)
 ===================

Cython/Compiler/Main.py

@@ -251,10 +251,11 @@ class Context(object):
 
     def search_include_directories(self, qualified_name, suffix, pos,
                                    include=False, sys_path=False):
-        include_dirs = tuple(self.include_directories)
+        include_dirs = self.include_directories
         if sys_path:
-            include_dirs = include_dirs + tuple(sys.path)
-        include_dirs = include_dirs + (standard_include_path,)
+            include_dirs = include_dirs + sys.path
+        # include_dirs must be hashable for caching in @cached_function
+        include_dirs = tuple(include_dirs + [standard_include_path])
         return search_include_directories(include_dirs, qualified_name,
                                           suffix, pos, include)