[Janther]

Every call into Slang's wasm that returns an object has to build a new JavaScript object from scratch. Each node's constructor called children() on its own Slang node, creating an array and a new object for every child. Instead, we now walk the tree once and collect all the metadata (locations and comments) before calling the constructors; SlangNode's constructor is now just a lookup.

There is a 10% improvement in the parsing speed after these changes and the constructor for each node is much cleaner.

Important changes:

• Instead of calling node.children() at each constructor, we walk the whole tree once using a Cursor.

  // This:
  for (const { node } of cst.children()) {
    ... 
  }
  // becomes:
  do {
    ...
  } while (cursor.goToNextSibling())

  This way we avoid creating an array of new JavaScript objects for each parent node.

• Instead of calling node.textLength on every NonterminalNode, and since we are already recursively walking the tree, we just use the pointer avoiding another call to the wasm.

  // This:
  for (const { node } of cst.children()) {
    const textLength = node.textLength.utf16;
    ...
  }
  // becomes:
  visitNonterminal(cursor, id, collected, offset);
    do {
      const node = cursor.node;
      if (node.isNonterminalNode()) {
        offset = visitNonterminal(cursor, node.id, collected, offset);
        ...
        continue;
      }
      const textLength = node.textLength.utf16;
      const end = offset + textLength;
      ...
      offset = end;
    } while (cursor.goToNextSibling())
    ...
    return offset;
  }

[Janther]

parking until #1756 is merged