Re: [commit: ghc] master: Fix pprPanic so that it doesn't throw away the SDoc part of the error. (e6ce335)

Erik de Castro Lopo <[email protected]> Wed, 5 Dec 2012 08:12:59 +1100

Newsgroups	gmane.comp.lang.haskell.cvs.ghc
Organization	Erik Conspiracy Secret Labs
Message-ID	<[email protected]>

Ian Lynagh wrote:

> I've reverted this: the Doc is passed in the PanicDoc constructor, so it
> shouldn't be necessary.
> 
> What problem were you trying to solve?

Well, pprPanic is defined as:

    pprPanic :: String -> SDoc -> a
    -- ^ Throw an exception saying "bug in GHC"
    pprPanic    = panicDoc

and panicDoc is defined as:

    panicDoc :: String -> SDoc -> a
    panicDoc    x doc = throwGhcException (PprPanic        x doc)

when the exception is throw it ends up in showGhcException which drops
the SDoc part of the message on the floor:

        PprPanic  s _ ->
            showGhcException (Panic (s ++ "\n<<details unavailable>>"))

I tried to convert the SDoc to a String in this code, but that resulted
in a circular import. The obvious solution was the one in my patch.

Erik
-- 
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/