Crash on reverseIndex

[migueldeicaza]

I caught the issue in the wild, the crash is:

    frame #3: 0x000000019475f134 libswiftCore.dylib`Swift._assertionFailure(_: Swift.StaticString, _: Swift.String, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never + 652
    frame #4: 0x0000000102b7f84c LaTerminal`CircularList.shiftElements(start=47, count=3, offset=1, self=0x0000000280bf5680) at CircularList.swift:169:9
  * frame #5: 0x0000000102beebe4 LaTerminal`Terminal.reverseIndex(self=0x00000001043e4ed0) at Terminal.swift:4937:26
    frame #6: 0x0000000102bbeb98 LaTerminal`closure #84 in Terminal.configureParser(collect=0 values, flag=77, self=0x00000001043e4ed0) at Terminal.swift:868:76

The issue is that shiftElements is being called with start=47, but the buffer itself only has 42 lines. The 47 is a combination of buffer.y = 21 and buffer.base = 26. And also notice that buffer.y = buffer.scrollTop which is why this path is triggered at all, originMode=false, usingMargins() = false

I was running top, and messing up the display with debug output from a background process, and I had refreshed it a few times, and I had just attempted to go to the background with control-z

The data was:
[0] = "\r"
[1] = "\u{1b}"
[2] = "["
[3] = "3"
[4] = "4"
[5] = "d"
[6] = "\u{1b}"
[7] = "["
[8] = "L"
[9] = "\u{1b}"
[10] = "["
[11] = "2"
[12] = "2"
[13] = ";"
[14] = "2"
[15] = "5"
[16] = "r"
[17] = "\u{1b}"
[18] = "["
[19] = "2"
[20] = "2"
[21] = ";"
[22] = "1"
[23] = "H"
[24] = "\u{1b}"
[25] = "M"
}

Cursor Vertical Absolute Position 34
Insert Line
Set Top and Bottom Margin to 22;25 (sets buffer.scrollBottom = 24, buffer.scrollTop=21)
Set Cursor Position 22;1
Reverse Index

Most likely, what we have here are two different buffers in action.