Comment by WorldMaker

I think the easiest trick here is to stop thinking about it as a parsing problem and consider it only as a lexing problem. A good lexer either doesn't throw out errors or minimizes error token states, and a good lexer gets back to a regular stream of tokens as quickly as it can. This is why we trust "simple" lexers as our syntax highlighters in most IDEs, they are fast, and they handle unfinished and malformed documents just fine (we write those all the time in our processes in our editors).

My experience many years back with using just a syntax highlighting tuned lexer to build character-level diffs showed a lot of great promise: https://github.com/WorldMaker/tokdiff