Deadlock during Search and Replace

[Treit]

I have a 100% reproducible hang when starting with this text:

This is a test.This is a test.This is a test.This is a test.This is a test.This is a test.

and then attempting to replace the word 'this' with the emoji 😩

See here:

In this screenshot I have hit the Replace All button and edit.exe is completely hung.

[lhecker]

It's impressive how this immediately reproduces but even running this in a debug build under a debugger it's not really obvious why this happens. It's stuck in the search loop though and never progresses from offset=4 after the first replacement.

[rhubarb-geek-nz]

it's not really obvious why this happens

I don't know how Rust works but is is common in other languages that if you are enumerating over something, you can't change the underlying collection during the enumeration.