[dschrempf]

This is a followup of #4726.

Feed stdin from an empty file.

The test explains the behavior:

-- 1. Support `stdin`
module TIO where

{- Feed `stdin` with empty data.

Avoid server hangs indefinitely, waiting for `stdin` to terminate.

Shows a clear error message.

>>> getLine >>= print
<stdin>: hGetLine: end of file
-}

@xsebek

Fixes #2913.

[dschrempf]

Somehow

cabal run func-test -- -p '/eval plugin sends progress reports/'

times out.

Any ideas?

[dschrempf]

The cause of the timeout was a deadlock.

1. The server reads messages from stdin, blocking the handle, waiting for the next message.
2. The eval plugin runs in the same process. The getLine wants to read the same handle, waiting for the server lock to be released.
3. Nothing happens until the timeout is reached.

The reason was to clone the stdin handle, similar to what we already do for stdout.

In detail, the original stdin and stdout are duplicated and exclusively used for the JSON-RPC connection. The stdin is closed (end of file), tested by the eval plugin test. stdout is redirected to stderr (stray messages end up in the logs).

[VeryMilkyJoe]

Just a little nit about documentation.
Thank you for this, I think it's really cool that you are working on the eval plugin!

[VeryMilkyJoe]

I don't really understand what this means, specifically what "around a statement".

[dschrempf]

Yea.. internals of the evil plugin; it should be explained in a better way.
I have updated the documentation. A opy of the new version is:

-- | Phases required to capture standard handles
--
-- Phases of the @eval@ plugin:
-- - fire up a GHCi session
-- - inject code into the GHCi session
-- - run the code
-- - capture the output
--
-- The code injected into the GHCi session contains a setup and a teardown
-- preparing and closing the involved handels, see 'captureSetup' and
-- 'captureTeardown'.

[VeryMilkyJoe]

Thank you, just a typo then we can merge!

[dschrempf]

🎉 thanks for the review @VeryMilkyJoe !