Show syntax error from Lezer parse

v6
3

Amazingly helpful answer in four lines!

In case this is useful to others, here is a working extension:

import {syntaxTree} from "@codemirror/language"
import {linter} from '@codemirror/lint'

function simpleLezerLinter() {
  return linter(view => {
    const {state} = view
    const tree = syntaxTree(state)
    if (tree.length === state.doc.length) {
      let pos = null
      tree.iterate({enter: n => {
        if (pos == null && n.type.isError) {
          pos = n.from
          return false
        }
      }})

      if (pos != null)
        return [{from: pos, to: pos+1, severity: 'error', message: 'syntax error'}]
    } 

    return []
  })
}
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