[biellls]

A simple approach might be that if the resulting exit code is not 0 it won't be used to complete in the future.

[Eavolution]

That'd have the problem of tools like grep returning nothing, having an exit code of 1, but being a perfectly valid thing to suggest in the future.

[starttoaster]

When you're writing, building, and executing code, I would not expect a 0 exit code every time.

[KRAKRISMOTT]

The fish approach