[Haskell-cafe] Significant changes in -Wall for GHC 7.10
omari at smileystation.com
Tue May 5 16:35:43 UTC 2015
I was basing this solely off the documentation:
so this may just be a documentation bug. Someone emailed me off-list and
said he reported it:
On Tue, May 5, 2015 at 12:25 PM, Edward Z. Yang <ezyang at mit.edu> wrote:
> Hello Omari,
> Just to double check, could you send us a program which fails
> to produce warnings on 7.10, which does produce warnings on 7.8,
> and the command line arguments to run it?
> I tried the following test:
> [ezyang at hs01 ghc-bisect]$ cat A.hs
> module A where
> -- f :: Bool -> Bool
> -- f x = x && (\x -> x) x
> g :: IO ()
> g = do (readLn :: IO Int)
> return ()
> [ezyang at hs01 ghc-bisect]$ ghc -c A.hs -Wall -fforce-recomp
> A.hs:5:9: Warning:
> A do-notation statement discarded a result of type ‘Int’
> Suppress this warning by saying ‘_ <- (readLn :: IO Int)’
> or by using the flag -fno-warn-unused-do-bind
> [ezyang at hs01 ghc-bisect]$ ghc --version
> The Glorious Glasgow Haskell Compilation System, version 7.10.1
> This is 7.10 that is distributed by Arch Linux. I haven't
> tried any other distributions, including the pre-built binaries.
> Excerpts from Omari Norman's message of 2015-05-05 07:54:59 -0700:
> > I noticed some significant changes to the flags included with -Wall in
> > 7.10. Many flags that were previously included in -Wall are now not
> > included. These include:
> > -fwarn-type-defaults
> > -fwarn-name-shadowing
> > -fwarn-missing-signatures
> > -fwarn-hi-shadowing
> > -fwarn-orphans
> > -fwarn-unused-do-bind
> > -fwarn-trustworthy-safe
> > I can't find any mention in the release notes of this change in behavior.
> > I was wondering what the rationale is for these changes? Any link to
> > relevant discussion would be appreciated if it exists.
> > Also, what opinion do people have? I previously kept my code -Wall
> > but sometimes that would be a pain. For instance I would munge local
> > so they wouldn't trigger -fwarn-name-shadowing, and I would add
> > to integers so they wouldn't trigger -fwarn-type-defaults. In fact, I
> > noticed this change in behavior in 7.10 because I was considering dumping
> > -Wall, and when I looked at the 7.10 manual I saw that it does not enable
> > -fwarn-name-shadowing. (I still use 7.8 but Google pulled the 7.10
> > manual.) Does this change indicate that people were finding -Wall too
> > onerous and, thus, not using it?
> > I do remember reading complaints about -fwarn-unused-do-bind being added
> > -Wall, but I previously felt dirty about name shadowing though I wondered
> > if munging names to avoid shadowing was actually worse.
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