Mushroom plot broken, with workaround
The "Mushroom Plot" function fails with this error:
Function 'string_to_int( string )' undefined. This script may require a more recent version of KoLmafia and/or its supporting scripts. (myshroom.ash, line 18)
This is with KoLmafia v20.4 r20201.
Can be fixed by changing the two occurrences of string_to_int() in planting/myshroom.ash to to_int(). This file was last modified on 30 January 2017.
That is not a "workaround". That is a "fix".
"myshroom.ash" is not built-in to KoLmafia. Perhaps you generated it with KoLmafia, on 20 Jan 2017 - and the template we used to generate planting scripts did, in fact, used to use that obsolete function - but when I removed the obsolete functions, I also changed the template to do what you found.
I also changed several popular user-supplied planting scripts - Auto Mushroom and MaxShrooms - to have the same fix.
Sorry for the inconvenience, but you found the solution. There is nothing that KoLmafia can (or needs to) do.
Indeed, that script had been loaded (and unused) for so long that I thought it was part of the build!