Foundry376/Mailspring · error

Menu items have colliding keys

Error message

Menu items have colliding keys

What it means

Warning while rendering Menu items: two items produced the same itemKey, so React reconciliation can swap/duplicate rows and selectedItemKey identifies the wrong item. Duplicate data (e.g. two contacts with the same email rendered as separate rows) is the usual cause.

Source

Thrown at app/src/components/menu.tsx:408

      if (React.isValidElement(content) && content.type === MenuItem) {
        return content;
      }

      const onMouseDown = (event: React.MouseEvent<HTMLDivElement>) => {
        event.preventDefault();
        const key = this.props.itemKey(item);
        this.setState({ selectedIndex: i, selectedItemKey: key });
        if (this.props.onSelect) {
          return this.props.onSelect(item);
        }
      };

      const key = this.props.itemKey(item);
      if (!key) {
        console.warn('Menu parent did not return an itemKey for item', item);
      }
      if (seenItemKeys[key]) {
        console.warn({ 'Menu items have colliding keys': item }, seenItemKeys[key]);
      }
      seenItemKeys[key] = item;

      return (
        <MenuItem
          key={key}
          id={this.props.listboxId ? `${this.props.listboxId}-option-${key}` : undefined}
          role={this.props.listboxId ? 'option' : undefined}
          onMouseDown={onMouseDown}
          checked={this.props.itemChecked && this.props.itemChecked(item)}
          content={content}
          selected={this.state.selectedIndex === i}
          suppressAriaSelected={!!this.props.onActiveDescendantChange}
        />
      );
    });

    const contentClass = classNames({

View on GitHub (pinned to 648c685d60)

Solutions

1. Deduplicate the items list before rendering
2. Make itemKey unique by combining fields (id + index or email + label)

When it happens

Trigger: Thrown at app/src/components/menu.tsx:408 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Foundry376/Mailspring@648c685d60 (2026-09-03). Data as JSON: /api/errors/3e87c0b48ed7d5b9. Report an issue: GitHub.