What causes "No such AST!" in phacility/phabricator?

Regenerate the AST by submitting code through the XHPAST panel again and use the new id

phacility/phabricator · warning · Exception

No such AST!

Error message

No such AST!

What it means

The XHPAST demo panel (PhabricatorXHPASTViewPanelController) loads a stored PhabricatorXHPASTParseTree row by its raw numeric id during willProcessRequest(). 'No such AST!' is the not-found signal, thrown as a plain Exception before any rendering happens; it is effectively a 404. The panel allows public access, so anonymous visitors probing ids see it too.

Source

Thrown at src/applications/phpast/controller/PhabricatorXHPASTViewPanelController.php:19

<?php

abstract class PhabricatorXHPASTViewPanelController
  extends PhabricatorXHPASTViewController {

  private $id;
  private $storageTree;

  public function shouldAllowPublic() {
    return true;
  }

  public function willProcessRequest(array $data) {
    $this->id = $data['id'];
    $this->storageTree = id(new PhabricatorXHPASTParseTree())
      ->load($this->id);

    if (!$this->storageTree) {
      throw new Exception(pht('No such AST!'));
    }
  }

  protected function getStorageTree() {
    return $this->storageTree;
  }

  protected function buildXHPASTViewPanelResponse($content) {
    $content = hsprintf(
      '<!DOCTYPE html>'.
      '<html>'.
        '<head>'.
          '<style type="text/css">
body {
  white-space: pre;
  font: 10px "Monaco";
  cursor: pointer;
}

View on GitHub (pinned to 5720a38cfe)

Solutions

Regenerate the AST by submitting code through the XHPAST panel again and use the new id
Verify the row exists in phabricator_xhpast_parsetree if the id is believed valid
Treat it as a 404: no data is corrupted and no action is strictly required

Defensive patterns

Strategy: validation

Validate before calling

// Resolve the tree before emitting or following a panel link.
$tree = id(new PhabricatorXHPASTParseTree())->load($id);
if (!$tree) {
  return new Aphront404Response();
}

Type guard

function xhpastTreeExists($id) {
  return (bool)id(new PhabricatorXHPASTParseTree())->load($id);
}

Try / catch

try {
  $response = $this->handlePanelRequest($request);
} catch (Exception $ex) {
  if (strpos($ex->getMessage(), 'No such AST!') !== false) {
    return new Aphront404Response();
  }
  throw $ex;
}

Prevention

Treat missing parse-tree ids as 404s in any custom routing
Regenerate ASTs rather than persisting ids long-term
Do not publish deep links to demo panel output; trees are transient

When it happens

Trigger: Visiting the XHPAST view panel with an id that has no phabricator_xhpast_parsetree row: a stale link to a garbage-collected tree, a database reset while old URLs persist, or a crawler probing sequential ids.

Common situations: Old bookmarks or pasted links to parsed AST dumps after the row was pruned; instance re-imports that dropped the xhpast tables; link scanners hitting the public panel.

Related errors

AI-assisted analysis of phacility/phabricator@5720a38cfe (2026-08-21). Data as JSON: /api/errors/a409fc3a7931a811. Report an issue: GitHub.