[svgdata] properties defined on layers are not exported in the corresponding svg element

[denis-migdal]

Preflight Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Search terms: svgdata

Describe the bug

When defining properties on a layer, and then exporting to SVG using the svgdata plugin, the properties are not included in the corresponding svg element.

To Reproduce
Steps to reproduce the behavior:

1. Enable the svgdata plugin
2. Create a new layer
3. Add a property to the layer
4. Add a new shape to this layer
5. Export the document as SVG
6. Open the SVG file in a text editor and search for the property.

Expected behavior

Properties defined on layers should be included in the <g> element corresponding to the layer.

Screenshots

NA

draw.io version (In the Help->About menu of the draw.io editor):

• draw.io version v29.3.0 (desktop)
• draw.io version v29.3.2 (web)

Desktop (please complete the following information):

• OS: Linux
• Browser: Firefox
• Browser Version: 146.0.1

I tested the problem in incognito/private mode with all browser extensions switched off, write "yes" below:

• NA

Additional context

Related issue: #5422 (comment)

[draw-io-triage-bot]

👋 Thank you for opening this issue!

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Summary: User reports that when using the svgdata plugin, custom properties defined on layers are not being exported to the corresponding SVG <g> elements in the exported file.

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📝 Additional Information Needed

To help us investigate this more effectively, could you please provide:

• Could you provide a sample SVG export showing the current output versus what you expect to see?
• What specific property names and values are you adding to the layer that aren't appearing in the SVG?
• Are you using custom properties or built-in draw.io properties on the layer?

📋 Bug Report Template

**Environment:**
- draw.io version: [e.g., web app / desktop 24.x.x / Confluence plugin]
- Browser (if web): [e.g., Chrome 120, Firefox 121]
- OS: [e.g., Windows 11, macOS 14, Ubuntu 22.04]

**Steps to Reproduce:**
1. Go to ...
2. Click on ...
3. See error

**Expected Behavior:**
What you expected to happen.

**Actual Behavior:**
What actually happened.

**Screenshots/Files:**
If applicable, add screenshots or attach the .drawio file.

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_{🤖 This is an automated response to help with initial triage. A human maintainer will review this issue. If you've provided all the requested information, no further action is needed - we'll get back to you soon!}

[denis-migdal]

I added a custom property "test: layout" to the "another" layer (ID Qs_A3q4Vq3TgkYnn16WV-6).

The generated tag is <g data-cell-id="Qs_A3q4Vq3TgkYnn16WV-6">.
It should be: <g data-cell-id="Qs_A3q4Vq3TgkYnn16WV-6" data-test="layout">.
Or better: <g data-cell-id="Qs_A3q4Vq3TgkYnn16WV-6" data-label="another" data-test="layout">.

Here the generated file: