This post discusses a possible fix for #1437
<https://github.com/leo-editor/leo-editor/issues/1437>: Leo-Bridge can be
wrong about an outline read from a file.
This is a tricky topic, so I want to walk myself, Bob, and other interested
parties through the problem and the fix.
In the first comment of #1437 Bob says:
"Before reading a file, Leo generates one or more nodes with GNX's for the
file. Usually this is harmless because the GNX's generated do not match any
of the GNX's in the outline being read. But when a generated GNX equals a
GNX in the outline being read, Leo is misled about the outline contents."
*Restating the problem*
LeoFrame.createFirstTreeNode allocates a vnode, c.hiddenRootNode, before
reading the file. That means that there is *no way* to ensure that
c.hiddenRootNode.gnx won't conflict with the vnodes in the file that is
about to be read.
This potential clash only happens when the bridge opens two or more .leo
files within a second or so.
leoBridge.py typically opens .leo files using g.openWithFileName. The call
chain is long and complex, so adding kwargs along the way is out of the
question.
*The fix*
Rev 6269bab in the gnx branch follows Bob's third solution, more or less.
Here are the details:
1. frame.createFirstTreeNode now sets c.hiddenRootNode.gnx to a dummy
value, but *only* when g.app.inBridge is True:
def createFirstTreeNode(self):
"""Create a new vnode as the root of the to-be-created tree."""
c = self.c
# #1437: Use a dummy gnx in the bridge.
gnx = '**dummy-gnx**' if g.app.inBridge else None
v = leoNodes.VNode(context=c, gnx=gnx)
p = leoNodes.Position(v)
v.initHeadString("NewHeadline")
# p.moveToRoot would be wrong: the node hasn't been linked yet.
p._linkAsRoot(oldRoot=None)
The guard on g.app.inBridge ensures that only the bridge can ever be
affected by the new code.
2. After reading the file, bridge.openLeoFile sets c.hiddenRootNode.gnx to
a value that doesn't conflict with any gnx in the just-read file:
# Existing code: make sure all new gnx's are unique.
g.app.nodeIndices.compute_last_index(c)
# #1437: Set c.hiddenRootNode.gnx:
g.app.nodeIndices.getNewIndex(v=c.hiddenRootNode)
Giving c.hiddenRootNode a valid (unique!) gnx should ensure that no other
part of Leo can be affected by the dummy gnx.
*Summary*
The new code is straightforward. Its effects should be isolated to only the
bridge itself.
Please let me know if I have misunderstood the problem, or its solution.
Edward
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