editor: Improve Evy web editor to use smarter indentation

[juliaogris]

Use smarter indentation in Evy web editor.

Whenever a new line is inserted, the editor will automatically:

• preserves indent of current line by default (we already had this).
• increases the indent after block opening keywords
  func on if else while for (new).
• updates the current line indent for end and else keywords:
  decreasing the indent if needed (new).

There are many edge cases. This is a best effort improvement. Current
line updating only happens if no selection is active - selection start
and end index are equal.

Fixes: evylang/todo#115

---

The main challenge of this PR is to a bunch of tedious manual testing of the editor.

I will try and write a longer Evy program in the web editor before merging.

[github-actions]

firebase-deployment for ea8b6d5

• apex: https://evy-lang-stage--455-d4a9dqdq.web.app
• discord: https://evy-lang-stage-discord--455-rt6mnwg3.web.app
• docs: https://evy-lang-stage-docs--455-duttu3ub.web.app
• gallery: https://evy-lang-stage-gallery--455-tir4owcq.web.app
• lab: https://evy-lang-stage-lab--455-bzhxsxi8.web.app
• learn: https://evy-lang-stage-learn--455-miipazzg.web.app
• play: https://evy-lang-stage-play--455-7qa8lpbg.web.app

[camh-]

I've managed to golf this down a little. I've put else in the second group in the regex (removed it from the end):

const matches = /^(\s+)?((func|on|if|else|while|for)\b)?(end\b)?/.exec(currentLine)

and have this code:

  event.preventDefault()
  let indent = matches[1] || ""
  let before = value.substring(0, selectionStart)
  const after = value.substring(selectionEnd)

  // Matches block-closing keywords, 'end' 'else'
  if (matches[4] !== undefined || matches[2] === "else") {
    // Decrease indent of current line, if indent of current and previous line equal.
    if (shouldDedent(indent, lines, currentLineNumber)) {
      const beforeCurrentLine = before.substring(0, before.length - currentLine.length)
      const dedentedCurrentLine = currentLine.substring(4)
      before = beforeCurrentLine + dedentedCurrentLine
      // Decrease indent
      indent = indent.substring(4)
    }
  }

  // Matches block-opening keywords, 'func' 'on' 'if' 'else' 'while' 'for'.
  if (matches[2] !== undefined) {
    // Increase indent.
    indent += "    "
  }

  const newValue = before + "\n" + indent + after
  const newIdx = newValue.length - after.length

I've test that and it seems to work locally.

[camh-]

🍏