When we're creating folds that contain other folds, we'll need the
region based on the new fold's row mapping to overwrite the regions
from the old folds. This commit ensures that the new region cleanly
slots in, replacing any regions it completely contains and splitting
regions that it only partially overlaps.
If there are multiple mappings following the start row of the delta
that span fewer screen rows than the delta, we collapse mappings to 0
screen rows until we have removed the number of rows specified by the
delta.
Expanding positive deltas expands the first mapping following the
start row as it did previously.
Inserting a mapping should never change the position of any existing
mappings on screen or in the buffer. It's simply a statement about a
range of rows in the buffer mapping to a range of existing rows on
screen, but shouldn't add or remove any rows. Adding and removing rows
on screen or in the buffer is the job of the applyBufferDelta and
applyScreenDelta methods.
If an exception is thrown while running an operation, we clear the
undo manager and re-throw it. But if we were in a transaction, we will
commit it in a `finally` block. If the transaction is set to null,
committing the transaction will then throw an exception which hides
the original exception… we don't want that. Now clear just empties the
current transaction out.
If 'foo' has not been set and has a default value of 1,
config.set('foo', 1) will not store the 1.
If 'foo' has been set to X and has a default value of 1,
config.set('foo', 1) will remove 'foo' from config
Lines that are all whitespace are considered trailing
whitespace and should display the indent guide.
But lines with leading and trailing whitespace should never
have the indent guide rendered in the trailing area.
We no longer need to restore selection ranges before and after
transactions now because selections are based on markers so they go
along for the ride for free. This allows us to delegate directly to
Buffer.transact from EditSession.
