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Comment by berkes | Hacker News Reader

Way before I consistently used step debuggers and would just "print-debug" println("why are you here?") or "raise-debug" raise new Error("huh?"), I tinkered with a step debugger, but found it too complex and hard. But I remember that it also allowed me to move backwards in the stack.

It allowed me to go some frames back - lines up, up in the stack. I don't recall the name of this debugger, nor what language it was. But I've never since seen this, yet very often wished I had it (for rust, javascript, python, mostly).

Did I misremember? Can such a thing exist? Does it exist?

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Time travel debugging is the category, but I can’t help you much more than that with the tool names.

While time-travel debugging would provide such capability, it is highly unlikely they are describing that due to timeframe and unfamiliarity with debuggers.

They are most likely describing the much simpler feature of having the debugger drop stack frames (by force nuking the stack) and then starting over (with all the other side effects that occurred in the “prior” execution still present). This is a fairly common feature for exploratory debugging, but has the obvious downsides of leaving lingering side effects so is only fit for use in non-production environments at best like other “edit-and-continue” features.

Time-travel debugging is something different – time-travel debugging means you can actually step backwards through the execution to try and see how you ended up with the bug.

Merely being able to inspect the state of (local) variables further up the stack frame is a much more limited proposition, even if it can still be useful.

> yet very often wished I had it (for […] javascript […] mostly)

Both Firefox's and Chrome/Edge's devtools allow you to do that, don't they? Click on an entry in the stack frame and it takes to the corresponding code line and shows you the state of the variables relevant at that point.

VB6 had it, and iirc you could even edit the code after stepping back to step forward on a different path. While trying to confirm that with a quick google I see that visual studio added stepping back in 2017. Though not sure it supports editing inline.

I distinctly remember C# having a similar capability many years ago too.

Of course, this was in the hyper expensive Visual Studio Enterprise IDE, not something like VS Code, which high school me totally paid 4 grand for and didn't pirate at all.

These days, features like these are making it to free or cheap tools.

In Java-world it's very common.

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