stanfordnlp/CoreNLP · error · RuntimeException

Tree is not a descendant of root.

Error message

Tree is not a descendant of root.

What it means

Trees.leftEdge(t, root) computes t's token position at the left edge by walking from root; the helper returns false when t is not reachable within root's subtree, so the public method throws RuntimeException.

Solutions

1. Ensure root is the actual containing tree of t (use the same Tree object hierarchy).
2. Pass the sentence's full Tree as root, not a sibling or unrelated subtree.
3. Catch RuntimeException and return -1 / handle the disjoint-tree case explicitly.

Example fix

// before
int edge = Trees.leftEdge(subtree, otherTreeRoot);
// after
if (Trees.isIn(subtree, root)) { int edge = Trees.leftEdge(subtree, root); }

// containment check
boolean contains(Tree root, Tree t) { for (Tree sub : root) if (sub == t) return true; return false; }

try { edge = Trees.leftEdge(t, root); } catch (RuntimeException e) { edge = -1; /* t not under root */ }

When it happens

Trigger: Calling Trees.leftEdge(t, root) where t belongs to a different tree than root, or t is not actually a descendant of root (e.g. a subtree copied out of the original tree, or two disjoint trees compared).

Common situations: Comparing nodes from parse trees of different sentences; using a stale subtree reference after re-parsing; mixing trees from gold and guess Treebanks in evaluation code.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• t insert tree after the
• ancestor: height cannot be negative
• Attempt to open file with null name
• Bad arguments: " + x + " and " + lambda
• Bad tree state:

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/6894c0ddc381b77e. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/trees/Trees.java:50

    }
    int maxHeight = 0;
    for (Tree child : t.children()) {
      maxHeight = Math.max(maxHeight, height(child));
    }
    return maxHeight + 1;
  }
  
  /**
   * Returns the positional index of the left edge of a tree <i>t</i>
   * within a given root, as defined by the size of the yield of all
   * material preceding <i>t</i>.
   */
  public static int leftEdge(Tree t, Tree root) {
    MutableInteger i = new MutableInteger(0);
    if (leftEdge(t, root, i)) {
      return i.intValue();
    } else {
      throw new RuntimeException("Tree is not a descendant of root.");
//      return -1;
    }
  }

  /**
   * Returns the positional index of the left edge of a tree <i>t</i>
   * within a given root, as defined by the size of the yield of all
   * material preceding <i>t</i>.
   * This method returns -1 if no path is found, rather than exceptioning.
   *
   * @see Trees#leftEdge(Tree, Tree)
   */
  public static int leftEdgeUnsafe(Tree t, Tree root) {
    MutableInteger i = new MutableInteger(0);
    if (leftEdge(t, root, i)) {
      return i.intValue();
    } else {
      return -1;

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