No, it’s not trivial and it does require thinking about your grammar before you decide to lock down your language design. A lot of languages have some pretty ob

No, it’s not trivial and it does require thinking about your grammar before you decide to lock down your language design. A lot of languages have some pretty obvious synchronization points though, like semicolons and curly braces. If all else fails you can always read up to the next semicolon or curly brace and dump whatever you get into a syntax error node, then keep going. This is especially true if you are implementing an LSP server and so you expect to regularly see incomplete lines simply because the user hasn’t finished typing them in yet. Ultimately what you really want is many different kinds of specialized error (and warning) nodes for different mistakes users might make. For example, in C++ the statement `auto x = 1,000,000;` is technically correct but probably not in the way the user wanted. So you put a warning node there to record that they might want to use `1'000'000` instead. If you see something like `auto x = 42\n if (y) {…`, then you might guess that there is a missing semicolon before the newline. If a speculative parse of the next line succeeds, then you put a MissingSemicolon node into the AST (instead of one saying that the “if” was unexpected), followed by whatever the speculative parse found. Now repeat that process for five years as you polish your compiler into a sparking user–friendly gem.