Add suspend for vty

[junjihashimoto]

This PR adds suspend-function for vty.

[noughtmare]

I think vty still doesn't handle the suspend signal properly, see #152 and jtdaugherty/vty#120. So I think this won't work properly.

[junjihashimoto]

In my environment, suspend and wake-up work.
After waking up, userForceRefresh is needed. I just type Control-L.
If we do not use this function, we always kill a editor to switch to a shell.
I hope jtdaugherty/vty properly supports suspend and wake-up.

[junjihashimoto]

I tried userForceRefresh by sigCONT. See below.
But this code does not work.

suspend :: FrontendState -> IORef Editor -> IO ()
suspend fs editorRef = do
    void $ installHandler sigCONT (Catch $ void $ readIORef editorRef >>= refresh fs) Nothing
    raiseSignal sigSTOP

[junjihashimoto]

I'll try setAttrs of vty after wake-up.

[simonmichael]

I hope jtdaugherty/vty properly supports suspend and wake-up.

+1, I wanted this today while using hledger-ui. Does this change need to be submitted as a PR to vty ?

[simonmichael]

@junjihashimoto: FWIW I used your code in another project, and just calling vty's refresh after the suspend call (so it gets executed when resumed) works well for me. (The part I haven't figured out is resetting the terminal attributes when suspending.)

[junjihashimoto]

Good, thx!
l'll try it.

[junjihashimoto]

@simonmichael
In my environment(ubuntu), calling vty's refresh works well, too.
Is suspendAndResume of jtdaugherty/vty#120 also doing the same thing?

[simonmichael]

@junjihashimoto sorry the details have slipped my memory, I will point to my solution recorded there and the source of suspendAndResume.