Format button breaks undo

[broady]

To reproduce:

1. Go to http://www.gopherjs.org/playground
2. De-indent the three lines in main
3. Press "Format"
4. Ctrl-Z repeatedly

What I see:

Corrupted text.

What I want to see:

Ctrl+Z undoes formatting, then continues to undo previous operations.

/cc @francesc

[dmitshur]

Thanks for reporting this with clear reproduce steps.

I can reproduce this both on http://www.gopherjs.org/playground/ AND on https://play.golang.org/ in latest stable version of Chrome.

The code for applying formatting is very straightforward, it simply overwrites the entire <textarea> content with the new formatted code.

Given that it's also a bug on the official Go Playground, I suspect it's a browser thing. Whatever the fix is there is likely to be applicable here as well.

---

Okay, I just tried the same steps in Firefox, and the issue does not occur there. It undoes the formatting and edits before it without issues.

So, given it's a browser bug (that's likely to be fixed in the future) and not a bug specific to GopherJS Playground, it should be reasonable to close this, right?

It's probably also a good idea to make a small repro case and submit a bug report to Chrome project, if it's not already a known/reported bug.

[dmitshur]

Tested in latest stable Safari (Version 9.1.2 (11601.7.7)) and the bug happens there too (on both playgrounds). So I suspect it might be a long-standing WebKit issue (and probably already reported, but not easy to fix).

[grantnelson-wf]

Format and our custom code edits (e.g. press enter will auto-indent the new line) will cause the built-in undo/redo to not work (a problem with prevent default or setting text directly). To deal with this issue, I added a simple undo/redo tracker that will keep track of code changes (format, custom code edits, default keypress, copy/paste, etc) and selection changes (to be able to replace selection to undone change and scroll change into view) to provide a must better undo/redo experience.