Nested category with blocks in parent should collapse when dragging block

[TannerGabriel]

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• I have searched for similar issues before opening a new one.

Problem

No response

Request

Currently, when a parent toolbox category contains blocks alongside nested categories, reopening the parent category after dragging a block requires a double click, since the category is not collapsed automatically. This creates unnecessary friction.

Expected behavior:

• If the parent category contains blocks: collapse the parent after a block is dragged, so reopening the nested category only requires a single click.
• If the parent category contains no blocks: keep the current behavior.

More context in this group discussion.

Reproduction Steps

1. Create sample app: npx @blockly/create-package app hello-world
2. Add a nested toolbox category with blocks in the parent category
3. Open the nested category
4. Drag a block onto the workspace
5. Try reopening the parent category (Requires double click)

Example toolbox config:

    {
      kind: 'category',
      name: 'Nested',
      categorystyle: 'text_category',
      contents: [
        {
          kind: 'block',
          type: 'text',
        },
        {
          kind: 'block',
          type: 'text_join',
        },
        {
          kind: 'category',
          name: 'Nested Level 2',
          categorystyle: 'text_category',
          contents: [
            {
              kind: 'block',
              type: 'text_join',
            },
            {
              kind: 'block',
              type: 'text_indexOf',
            },
            {
              kind: 'block',
              type: 'text_getSubstring',
            },
            {
              kind: 'block',
              type: 'text_changeCase',
            }
          ]
        }
      ]
    }
  ],
};

screenrecording-2025-09-29_11-39-15.mp4

[maribethb]

Hey @TannerGabriel this is definitely a bug, would you be interested in contributing a fix for it? If you'd like any pointers we'd be happy to do that. Otherwise I'm not sure when we will be able to fit this into our roadmap. Thank you!

I think the correct behavior is that if a collapsible category opens a flyout (i.e. it contains blocks or other flyout items that aren't just more categories) then dragging a block out should collapse the category. If expanding a category doesn't open a flyout, then the category should remain uncollapsed when one of its child category flyouts is closed.

[TannerGabriel]

I will probably have some time this weekend or next week to take a look.