From 80e8cf99e242333ff0fbf04f60a59f3af88da08a Mon Sep 17 00:00:00 2001
From: Piotr Tworek <tworaz@tworaz.net>
Date: Wed, 13 Jan 2021 00:12:49 +0100
Subject: [PATCH] base: Make Genode::List clang friendly.

Clang is generally fine with Genode::List and compiles code using it
without emitting any warnings. There is however one exception. Clang
fails hard when building base-hw/src/core/kernel/object.cc.
This is due to a call to Genode::List::remove made from
Object_identity::invalidate function. The error message clang
produces is:

  list.h:96:33: error: 'Genode::List<Kernel::Object_identity_reference>::Element::_next'
  is not a member of class 'const Kernel::Object_identity'
                              _first = le->List::Element::_next;
                                           ~~~~~~~~~~~~~~~^

When we look at the declaration of the Kernel::Object class on which
the remove method is called. as expected it does inherit Genode::List:

using Object_identity_list
	= Genode::List<Kernel::Object_identity>;

class Kernel::Object : private Object_identity_list
{
...
}

Given the error message we see that List::Element should be resolved to
Genode::List<Kernel::Object_identity>::Element, and not
Genode::List<Kernel::Object_identity_reference>::Element. But how does
clang manage to figure out we're talking about Object_identity_refecence
list here? Well, I admit I don't know the exact steps it takes to arrive
at this conclusion, but it is not entirely wrong. If we take a look at
what Kernel::Object_identity is we'll see:

class Kernel::Object_identity
: public Object_identity_list::Element,
  public Kernel::Object_identity_reference_list
{
...
}

Where as one can guess Object_identity_reference_list is defined as:

using Object_identity_reference_list
	= Genode::List<Object_identity_reference>;

Long story short Kernel::Object has Genode::List of both Kernel::Object_identity
and Kernel::Object_identity_reference in its inheritance chain and clang
is not really sure to which of those the code refers to in
Genode::List::remove method by using List::Element::.

The fix for this is relatively simple, explicitly state the full type of
the base class the code intends to refer to. Replacing List::Element,
with List<LT>::Element makes the code buildable with both clang and GCC.

Fixes #3990
---
 repos/base/include/util/list.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/repos/base/include/util/list.h b/repos/base/include/util/list.h
index e93cc53288..afe31a2404 100644
--- a/repos/base/include/util/list.h
+++ b/repos/base/include/util/list.h
@@ -76,11 +76,11 @@ class Genode::List
 		{
 			/* insert at beginning of the list */
 			if (at == 0) {
-				le->List::Element::_next = _first;
+				le->List<LT>::Element::_next = _first;
 				_first = const_cast<LT *>(le);
 			} else {
-				le->List::Element::_next = at->List::Element::_next;
-				at->List::Element::_next = const_cast<LT *>(le);
+				le->List<LT>::Element::_next = at->List<LT>::Element::_next;
+				at->List<LT>::Element::_next = const_cast<LT *>(le);
 			}
 		}
 
@@ -93,7 +93,7 @@ class Genode::List
 
 			/* if specified element is the first of the list */
 			if (le == _first) {
-				_first = le->List::Element::_next;
+				_first = le->List<LT>::Element::_next;
 
 			} else {
 
@@ -106,10 +106,10 @@ class Genode::List
 				if (!e->_next) return;
 
 				/* e->_next is the element to remove, skip it in list */
-				e->List::Element::_next = e->List::Element::_next->List::Element::_next;
+				e->List<LT>::Element::_next = e->List<LT>::Element::_next->List<LT>::Element::_next;
 			}
 
-			le->List::Element::_next = 0;
+			le->List<LT>::Element::_next = 0;
 		}
 };