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language servers have pushed things to inspecting source code while programmer has partially written code, so having a kind of (invalid-span content="garbage")

• duped 2y ago
  Language servers usually are designed around full/concrete syntax trees instead of ASTs for exactly this reason. Adding error nodes to the AST is a hack that hurts more than helps. More technically, language servers usually have a CST that they use to build the AST incrementally, and the AST contains references back to the CST that generated it. This is what allows you to handle incremental text edits and compile small deltas to the AST instead of the typical batch compiler design that attempts to parse everything all at once.
  • jenadine 2y ago
    What's wrong with error node in the ast? I've seen language server that completely ignores the parts with error, and I much prefer error nodes because then I still know there is something and these error node can still have children
    • duped 2y ago
      There are a few problems with errors-as-nodes in a syntax tree. An abstract syntax tree is a hierarchical representation of the program in the language's grammar - and errors are not members of the grammar (they're everything else!) There is also the problem that an error returned by a language server is a class of a "diagnostic" that includes syntax errors, semantic errors, warnings, lints, etc, associated with a span in the source code. It's much easier to think of diagnostics as a separate data structure that gets filled up during lexical/semantic analysis and associated with spans in the full syntax tree (you can even store them there as fields, but they don't necessarily have children). Then it's obvious how the structure gets created and fed back to the user. And finally, the whole point of an AST is to be a valid canonical representation of a program so the compiler query it drives doesn't have to do additional input validation. So it just makes the queries/compiler passes easier to write.
• deleted 2y ago
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