Live snippets break undo chains

[MichalHacks]

Bug Report

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You still see this issue?: Yes

Describe the bug

After a live snippet is activated and the text changed, the snippet activation cannot be practically undone as immediately after undoing, the snippet activates again.

This breaks the undo chain, as further undo actions just revert and reactivate the snippet, not allowing the user to reach earlier undo states.

To Reproduce

Steps to reproduce the behaviour:

Example 1:

[in math mode]

1. type vmat
2. ctrl + z (whole thing disappears)
3. ctrl + z (vmat snippet activates)

consecutive undo actions repeat step 2 and 3

Example 2:

[in math mode]

1. type sq
2. ctrl + z (whole thing disappears)
3. ctrl + z (sq snippet activates)

consecutive undo actions repeat step 2 and 3

Expected behaviour

After undoing a snippet activation, the program allows for undoing further into the undo chain.

Example:

Visible text:      sq    ->        \sqrt{}       ->    sq    -> [previously typed text]
User action:   Type "sq" -> [snippet activation] -> Ctrl + Z ->        Ctrl + Z

Logs

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Unrelated

Screenshots

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Desktop

• OS: Windows 10
• VS Code version: 1.39.1
• Extension version: v0.4.14