mermaid-js/mermaid · error · Error

Line definition not found

Error message

Line definition not found

What it means

Thrown at the end of drawArrow when the local variable lineDef is still undefined after every geometry branch was evaluated. lineDef is only assigned inside nested if/else blocks keyed on direction (TB/BT/LR), arrow rerouting, and coordinate relationships (p1.x vs p2.x, p1.y vs p2.y). If none of those conditions match — most notably when a commit position coordinate is NaN, making every comparison evaluate false — lineDef is never assigned and the safety check fires.

Source

Thrown at packages/mermaid/src/diagrams/git/gitGraphRenderer.ts:840

      if (p1.y > p2.y) {
        if (commitB.type === commitType.MERGE && commitA.id !== commitB.parents[0]) {
          lineDef = `M ${p1.x} ${p1.y} L ${p2.x - radius} ${p1.y} ${arc} ${p2.x} ${
            p1.y - offset
          } L ${p2.x} ${p2.y}`;
        } else {
          lineDef = `M ${p1.x} ${p1.y} L ${p1.x} ${p2.y + radius} ${arc2} ${p1.x + offset} ${
            p2.y
          } L ${p2.x} ${p2.y}`;
        }
      }

      if (p1.y === p2.y) {
        lineDef = `M ${p1.x} ${p1.y} L ${p2.x} ${p2.y}`;
      }
    }
  }
  if (lineDef === undefined) {
    throw new Error('Line definition not found');
  }
  svg
    .append('path')
    .attr('d', lineDef)
    .attr(
      'class',
      'arrow arrow' + calcColorIndex(colorClassNum!, THEME_COLOR_LIMIT, useColorTheme)
    );
};

const drawArrows = (
  svg: d3.Selection<d3.BaseType, unknown, HTMLElement, any>,
  commits: Map<string, Commit>
) => {
  const gArrows = svg.append('g').attr('class', 'commit-arrows');
  [...commits.keys()].forEach((key) => {
    const commit = commits.get(key);

View on GitHub (pinned to d93e9c88c0)

Solutions

1. Treat this as a symptom: inspect the commit positions passed to drawArrow and look for NaN/undefined coordinates, then fix the upstream layout that produced them.
2. Temporarily switch the gitGraph direction to LR (default) to see if the throw disappears, isolating it to TB/BT geometry code.
3. Reduce the diagram to the smallest case that reproduces and report it upstream with the diagram text and mermaid version.
4. Upgrade to the latest mermaid patch release — geometry edge cases are fixed frequently.

function positionsAreFinite(commitPos: Map<string, {x:number;y:number}>): boolean {
  for (const p of commitPos.values()) {
    if (!Number.isFinite(p.x) || !Number.isFinite(p.y)) return false;
  }
  return true;
}

try {
  await mermaid.render('g', diagramText);
} catch (e) {
  if (e instanceof Error && /Line definition not found/.test(e.message)) {
    // This is a downstream symptom of bad positions; ask user to simplify the graph
    showUserError('Unable to compute arrow geometry. Try simplifying the gitGraph or switching direction.');
  } else {
    throw e;
  }
}

When it happens

Trigger: A commit position stored in commitPos has x or y equal to NaN, so comparisons like p1.y < p2.y, p1.y > p2.y, and p1.y === p2.y are all false and no branch runs; or an unexpected dir value outside TB/BT/LR; or a rerouting path whose sub-conditions all miss.

Common situations: Usually a downstream symptom of error 60 or of a layout computation producing NaN (e.g. division by zero in getCommitPosition); appears after changing theme/layout config that alters commit spacing math; rare in stable releases.

Related errors

• Position not found for branch ${branch.name}
• Commit positions not found for commits ${commitA.id} and ${c
• Groups within groups are not allowed in Kanban diagrams
• start should have been set during first phase
• end should have been set during first phase

AI-assisted analysis of mermaid-js/mermaid@d93e9c88c0 (2026-08-12). Data as JSON: /api/errors/19af0a408659ccc0. Report an issue: GitHub.