Tab completion in the shell seems to stop working after other code is already on the input line. It seems like this dates to the introduction of linenoise as a readline replacement.

MongoDB shell version: 2.1.0-pre-
> f=function(){} // define empty function
function () {
}
> f.toL<tab>ocaleString() // hit tab after "f.toL" and it completes (I added the ")")
function () {
}
> typeof f.toL<tab> // nothing, no completion
undefined
> g=f.toL<tab> // nothing, no completion

The behavior is the same in 1.9.1, 2.0.0 and the current code. This works in 1.8.4-rc1-pre- built from source today.

Tested in Ubuntu 11.04 with gnome terminal.