[CustomTextEditor extensions] Untitled document content is lost when doing "Reopen with..." custom text editor

[Ark-kun]

Does this issue occur when all extensions are disabled?: Yes/No

• VS Code Version: 1.67.2
• OS Version: Windows 10

When doing "Reopen with... Cat Scratch" on untitled file, the content is lost

Steps to Reproduce:

1. Open the https://github.com/microsoft/vscode-extension-samples/tree/0d36653b0da5041f49fe049e34f6d8671f8e1002/custom-editor-sample
2. Augment the catScratchEditor.ts updateWebview code to add logging: console.log("updateWebview called. Document length = " + document.getText().length);
3. Press F5 to debug the extension.
4. Double-click on the tab bar to open new "Untitled 1" tab.
5. Paste valid catScratch content:

{
  "scratches": [
    {
      "id": "8lYOoWqz2rHtPuhvnZ43eMx1mG6WnFrm",
      "text": "😸",
      "created": 1584577931699
    },
    {
      "id": "aZ57bJUEaXZ5wuBAX6NfGuj85Y6iw84N",
      "text": "😻",
      "created": 1584577933329
    }
  ]
}

6. Use "Reopen with..." / "Cat Scratch" on the "Untitled 1" file.
7. Observe: That the editor has no scratches
8. Observe "updateWebview called. Document length = 0" in the log. The document content got lost

I expect the untitled document content to be preserved when reopening with custom editor.

2022-05-22.18-15-33.mp4

[VSCodeTriageBot]

Thanks for creating this issue! It looks like you may be using an old version of VS Code, the latest stable release is 1.67.2. Please try upgrading to the latest version and checking whether this issue remains.

Happy Coding!

[mjbvz]

One bug per issue

Just tracking the first one here. Please open separate issues for the others

[Ark-kun]

Please open separate issues for the others

Done.