The reason is that the per-node updates used for Reroute node type inheritance are not supposed to be looking at connected nodes, they are purely for "local" updates. For this sort of "global" update which requires depth-first search, the update function on the node tree level must be used instead.
By holding shift and "cutting" a node link a new reroute helper node can be inserted. This consists of a single socket that can be used to insert additional connection points into a link. This can be used to keep a connection point in the tree when deleting a node, or to control the path of long connections for layout cleanup.
There are a number of features that use a kind of "internal linking" in nodes:
1. muting
2. delete + reconnect (restore link to/from node after delete)
3. the new detach operator (same as 2, but don't delete the node)
The desired behavior in all cases is the same: find a sensible mapping of inputs-to-outputs of a node. In the case of muting these links are displayed in red on the node itself. For the other operators they are used to relink connections, such that one gets the best possible ongoing link between previous up- and downstream nodes.
Muting previously used a complicated callback system to ensure consistent behavior in the editor as well as execution in compositor, shader cpu/gpu and texture nodes. This has been greatly simplified by moving the muting step into the node tree localization functions. Any muted node is now bypassed using the generalized nodeInternalRelink function and then removed from the local tree. This way the internal execution system doesn't have to deal with muted nodes at all, as if they are non-existent.
The same function is also used by the delete_reconnect and the new links_detach operators (which work directly in the editor node tree). Detaching nodes is currently keymapped as a translation variant (macro operator): pressing ALTKEY + moving node first detaches and then continues with regular transform operator. The default key is ALT+DKEY though, instead ALT+GKEY, since the latter is already used for the ungroup operator.
Now, compositing, shading and texture nodes have a consistent muting system, with default behaving as previous (for compo), and which can be optionaly customized by each node.
Shader nodes are also GLSL muted.
However, Cycles is currently unaware of muted nodes, will try to address this…
This prevents access to non-existent typeinfo during type initialization,
when node types have been removed and such nodes are deleted from older files.
All blenkernel functions now only set the node->update flag instead of directly
calling the update function. All operators, etc. calling blenkernel functions
to modify nodes should make a ntreeUpdate call afterward (they already did that
anyway).
Editor/RNA/renderer/etc. high-level functions still can do immediate updates by
using nodeUpdate and nodeUpdateID (replacing NodeTagChanged/NodeTagIDChanged
respectively). These old functions were previously used only for setting
compositor node needexec flags and clearing cached data, but have become generic
update functions that require type-specific functionality (i.e. a valid typeinfo
struct).
This would previously break because begin/end functions for each tree type still have some checks of the ntree->execdata pointer in them, despite the intended use of execdata instances instead of trees themselves for execution data storage. This is an artifact of the old execution system that required these checks to be made in the functions to avoid multiple execution of top-level trees. Now these functions take an additional argument, so group nodes can prevent them from setting and checking the nodetree->execdata pointers.
This branch adds mostly organizational improvements to the node system by renaming the node folders and files. A couple of internal features have been added too.
Detailed information can be found on the wiki page:
http://wiki.blender.org/index.php/User:Phonybone/Particles2010
