Replace onDidChange with an enhanced version of onDidChangeText

[maxbrunsfeld]

Background

The TextBuffer.onDidChange method has long been a source of performance problems because it causes its callback to be called for each individual change that happens to a TextBuffer. This behavior makes it very expensive to make a series of small changes to a buffer with any change observers. This is important for multi-cursor editing, and it also has shaped other decisions about how to mutate buffers, encouraging preprocessing strings before inserting them into text buffers rather doing the preprocessing in the buffer itself.

A while ago, we added a more efficient way of observing changes to buffers - TextBuffer.onDidChangeText. Callbacks passed to this method get called only once per transaction, and are passed an array of the consolidated changes that occurred in that transaction.

Solution

This PR unifies onDidChange and onDidChangeText; they are now identical. Listeners get called once per transaction.

I'm ensuring backwards-compatibility for existing users of onDidChange by synthesizing the old event properties oldRange, newRange, oldText and newText. For example, if two separate changes occur in a transaction, oldRange will be the smallest possible Range that encompasses both of the changes.

The oldText and newText properties are now deprecated. Callers who are interested in the text that was inserted or removed should use the changes property to examine individual changes.

/cc @nathansobo

[nathansobo]

I guess it's not worth the hassle of deprecating it? Probably not.

[maxbrunsfeld]

I think we should, but I thought we should do that in a second pass, after we remove all of our own uses of it.

[maxbrunsfeld]

Same with oldText and newText. I want to deprecate them soon.

[nathansobo]

👍