type holes related ghc panic

sample.hs:9:13:
    Couldn't match expected type ‘t’ with actual type ‘()’
      ‘t’ is untouchable
        inside the constraints ()
        bound by the inferred type of foo :: Meta -> t1
        at sample.hs:(6,1)-(9,17)ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.0.0 for x86_64-unknown-linux):
        No skolem info: t_avJ[sk]

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug


sample.hs:
module Blah where

newtype Meta = Meta ()

foo (Meta ws1) =
    let copy :: _
        copy w from = copy w 1
    in copy ws1 1

Trac metadata

Trac field	Value
Version	7.10.1-rc2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

assigned to @trac-thomasw

Trac metadata

Trac field	Value
Differential revisions	→ D646

mentioned in commit e9d72cef

I'm terribly sorry for, once again, bringing up tickets late in the release cycle... but can the above fix be included in ghc 7.10? I'm getting:

~/devel/test$ ghci Blah.hs 
GHCi, version 7.10.0.20150323: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Blah             ( Blah.hs, interpreted )

Blah.hs:7:17:
    Found hole ‘_’ with type: t2 -> a1 -> t3
    Where: ‘t2’ is a rigid type variable bound by
                the inferred type of copy :: Num a1 => t2 -> a1 -> t3
                at Blah.hs:8:9
           ‘t3’ is a rigid type variable bound by
                the inferred type of copy :: Num a1 => t2 -> a1 -> t3
                at Blah.hs:8:9
           ‘a1’ is a rigid type variable bound by
                the inferred type of copy :: Num a1 => t2 -> a1 -> t3
                at Blah.hs:8:9
    To use the inferred type, enable PartialTypeSignatures
    Relevant bindings include
      ws1 :: () (bound at Blah.hs:6:11)
      foo :: Meta -> t3 (bound at Blah.hs:6:1)
    In the type signature for ‘copy’: _
    In the expression:
      let
        copy :: _
        copy w from = copy w 1
      in copy ws1 1
    In an equation for ‘foo’:
        foo (Meta ws1)
          = let
              copy :: _
              copy w from = copy w 1
            in copy ws1 1

Blah.hs:8:9:
    No instance for (Num a)
    When checking that ‘copy’ has the specified type
      copy :: forall t t1 a. t -> a -> t1
    Probable cause: the inferred type is ambiguous
    In the expression:
      let
        copy :: _
        copy w from = copy w 1
      in copy ws1 1
    In an equation for ‘foo’:
        foo (Meta ws1)
          = let
              copy :: _
              copy w from = copy w 1
            in copy ws1 1

Blah.hs:9:13:
    Couldn't match expected type ‘t’ with actual type ‘()’
      ‘t’ is untouchable
        inside the constraints ()
        bound by the inferred type of foo :: Meta -> t1
        at Blah.hs:(6,1)-(9,17)ghc: panic! (the 'impossible' happened)
  (GHC version 7.10.0.20150323 for x86_64-apple-darwin):
	No skolem info: t_avM[sk]

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

Also, this is not mission critical for me! So if it's postponed to a later release then it's no problem.

changed milestone to %7.10.1

added 1 deleted label

changed milestone to %7.10.2

Moving to GHC 7.10.2.

closed

Sorry, the patch in question is a bit tricky to merge as it has some dependencies. We may be able to revisit this one for 7.10.2, so I've pushed it off to said milestone.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

reopened

unassigned @trac-thomasw

Trac metadata

Trac field	Value
Resolution	ResolvedFixed → Unresolved

assigned to @trac-thoughtpolice

mentioned in issue #10356 (closed)

I'll put this into the 7.10.2 merge queue so that Austin looks at it again

added 1 deleted label

closed

removed milestone

I looked at it again, and I'm still inclined to leave it out. :) It would be possible to remove the bits from the redundant superclass warning patch that touch it, but it looks like there have been some other various changes resulting in quite a few hunks that don't match up.

So, unless someone Really Really needs it (or would like to backport the patch themselves!), I'd prefer to keep this one pointed to 7.12.1.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

mentioned in issue #10403 (closed)

mentioned in issue #10764 (closed)

changed milestone to %8.0.1

Milestone renamed

mentioned in issue #10999 (closed)

mentioned in commit f86fb5e5

Can #10946 (closed) be in any way related to this?

mentioned in issue #11059 (closed)

Too bad this did not make it into 7.10.3. The bug happens when trying out the code that explains how to derive unsafeCoerce from GND+TypeFamilies if we had not roles.

(This comment has little nutritional content.)

mentioned in issue #11347 (closed)

added compiler crash label

added Pnormal label