The recommended way forward is to use the SyntaxClassifier on the Swift
side.
By removing the C++ SyntaxClassifier, we can also eliminate the
-force-libsyntax-based-processing option that was used to bootstrap
incremental parsing and would generate the syntax map from a syntax
tree.
This patch changes the syntax map data structure it uses to be offset based
rather than line/col based in order to avoid calling getLineAndColumn for the
start and end offset of every token. This removes the 30% of time spent in
getLineAndColumn for this request in large files (rdar://problem/28965123).
The logic for returning the affected range and the token ranges to highlight
following an edit also made several assumptions that no longer hold. This
patch changes it to compare the syntax maps from before and after the edit,
find the first mismtaching tokens from the start and end of the syntax maps
and return the tokens in that range (adjusted to line boundaries). This fixes
syntax highlighting issues with interpolated multi-line strings
(rdar://problem/32148117) and block comments.
With the above changes the per-keystroke time spent for syntax highlighting
(with sematic info disabled) dropped from ~80ms to just under 50ms for a
12KLOC file.
