GHCi (or haskeline?) confused by non-single-width characters
Hi, there's an issue in the GHCi prompt.
To reproduce:
- Do everything in Linux (I don't have other operating systems); I'm using a version of the gnome 2 gnome-terminal.
- Use the following to colourise the prompt in GHCi:
echo -e :set prompt '"\033[32;1m%s\033[34;1m>\033[0m "' >> ~/.ghc/ghci.conf
- Import quite a few modules (say, 5 to 10 should be enough)
- Give the prompt enough text that it wraps around. It's best if you start the text with -- so that it's a comment and doesn't produce any output. For example, say I entered "-- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb", I now see the following:
- Types Control.Monad.Writer Control.Monad Data.Functor Control.Applicative Data.Monoid> -- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
(do note that the first set of b's is located on the same line as the prompt, and the second is located under the prompt)
- Press Enter. You should now see:
- Types Control.Monad.Writer Control.Monad Data.Functor Control.Applicative Data.Monoid> -- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
- Types Control.Monad.Writer Control.Monad Data.Functor Control.Applicative Data.Monoid>
- Press Ctrl-P or the up arrow key to select the previous history item. You will now see the following:
- Types Control.Monad.Writer Control.Monad Data.Functor Control.Applicative Data.Monoid> -- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
- Types Control.Monad.Writer Control.Monad Data.Functor Control.Applicative Data.Monoid> -- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
- Press Ctrl-A or the Home cursor key to go to the beginning of the text entry, and then type X. You will now see the last prompt to be:
- Types Control.Monad.Writer Control.Monad Data.Functor Control.Applicative Data.Monoid> -- bbbbbbbbbbbbX-- bbbbbbbbbbbbbbbbb
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
- If you press Enter, you will find out that prompt was actually (without line breaks):
X-- bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
I tried resizing the terminal window to 45 chars to make the lines above shorter; I imported Data.Monoid and Data.Functor in a new GHCi. The prompt contained garbage, most likely badly wrapped escape codes. See attachment.
As both likely are a single bug in disguise, I include both reports in this ticket.
Creating a test case for whether things actually work in a terminal might be difficult, but creating test for whether things get wrapped correctly (and not testing how things work out in a terminal) should be simple if annoying.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.8.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | GHCi |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | hvr |
| Operating system | |
| Architecture |