For matching `// // //~...` or `////~` which wouldn't be so rare if commenting out nested blocks (albiet probably not common in compile-fail).

Removing the `~` is alright when you only care about one line, but when you want to quickly remove a block or few from adding noise to the test output that's not so quick when you've got multiple expected errors in the block. Especially when you're just going to be adding them back after a few minutes. I've ended up just ripping parts out into a scratchpad to overcome this before, but it's not ideal.