You won't find anything about this in the man page on your desktop, nor the usage information for
adb because this isn't an
adb command. Remember that
adb shell foo starts a shell on the device and runs the command
foo there. It would be like looking in the
ssh man page to find out what
ssh myserver rm -rf * does.
The command you want help with is
ime list, and it only exists on the device, not your desktop. Running
adb shell ime (with no further arguments) prints out the usage information for this command.
usage: ime list [-a] [-s]
ime enable ID
ime disable ID
ime set ID
The list command prints all enabled input methods. Use
the -a option to see all input methods. Use
the -s option to see only a single summary line of each.
The enable command allows the given input method ID to be used.
The disable command disallows the given input method ID from use.
The set command switches to the given input method ID.
"Enabled" in this description doesn't refer to the "enabled" field in the manifest (that is, the one printed out under
ServiceInfo), but rather whether the IME is turned on in the settings. It might be a little confusing to have two different things called "enabled", but don't forget that
adb is a debugging tool for programmers, who are expected to understand such things. End-users shouldn't need to run this command, since the list of IMEs is accessible through the device settings.
From this description, if you get output with
ime list -a but not
ime list, that tells you that no input methods are currently enabled in the settings.