Variables View Loses Expansion State when Stepping

[ParOvBroadcom]

Description

When using the resume, step next or step in functions, the scope tree in the Variables view refreshes completely in Theia, this leads to a collapsed tree, while the tree in VSC remains to the previous state and leaves any expanded part as it is, by just refreshing whatever needs to. Is there a way to do the same in Theia?

Reproduction Steps

Start a debug session using DAP through Theia. When stopped in a specific breakpoint expand the scope and maybe some of the variables. Resume or step in or step over to the next breakpoint. The variable tree is completely disappearing and reappearing (really fast) and thus it is collapsed to the original scope only

Windows 10 and Theia version: 0.11.0

Diagnostics:
No diagnostics

[tsmaeder]

Changed the title to reflect the problem being described. Yeah, this behaviour is annoying.

[tolusha]

I can't reproduce. Is it os or browser specific issue?

[tolusha]

@ParOvBroadcom Is it still actual?

[akosyakov]

It could be timing issue, we debounce with 400ms:

theia/packages/debug/src/browser/view/debug-variables-source.ts

Line 41 in dbe5b5a

protected readonly refresh = debounce(() => this.fireDidChange(), 400);

@ParOvBroadcom Could you provide more concrete steps?

Maybe it is not even reproducible locally (i.e. VS Code does not do a remote call), but with some latency. @ParOvBroadcom Do you run locally?

[ParOvBroadcom]

It doesn't work properly in either way (resume or step over)
First having a running session

Then expanding the local variables

Clicking on Resume

It collapses the Local variables

Expanding again the variables

Clicking on step over

Collapses the local variables also

[akosyakov]

@ParOvBroadcom Is there a way to run your debug adapter or reproduce without it? It does not seem to happen with other.

[ParOvBroadcom]

@akosyakov What do you mean without "it"? This happens in Theia, but not in VScode.

[tolusha]

We need a debugger to reproduce the issue,
It can't be reproduced neither with node nor java debug.

[ishche]

It could be timing issue, we debounce with 400ms:

theia/packages/debug/src/browser/view/debug-variables-source.ts

Line 41 in dbe5b5a

protected readonly refresh = debounce(() => this.fireDidChange(), 400);

I increase debounce and it makes things better.
@akosyakov seems you right about it. We have pretty big delays in communication to target.

@tolusha, unfortunately, we can't provide our debugger.

[akosyakov]

@ishche How much do you need to increase?

[tolusha]

@akosyakov
@ishche
I've submitted a draft PR to check if proposed solution make sense.
#6734

[tsmaeder]

To me it seems we need to disassociate the expansion state of a particular stack frame (or whole stack) from the variables view: when we switch between active stack frames (be it by stepping or by selecting a different thread), we want to restore the expansion state we had before. Since the tree contents are switched out, the tree cannot hold that state.

This state should not be located in the "domain model", but in a separate "presentation model" that has a policy on how many variable expansion states to remember (maybe a fixed LRU or something similar).