#5884: GHC panics while trying to derive a Generic instance for Complex a
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Reporter: mux | Owner: dreixel
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Compile-time crash
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by guest):
I just ran into the same issue. The following conditions are required to
reproduce:
- the type we are trying to derive must be defined in a different module
- that module must be compiled, not interpreted
- the type we are trying to derive must have at least one non-phantom
type variable argument
In short if we define these types in a module:
{{{
data A = A Int
data X a = X Int
data Y a = Y a
}}}
Compile this module and then import it into another module and derive some
instances:
{{{
deriving instance Generic A -- works
deriving instance Generic (X a) -- works
deriving instance Generic a => Generic (X a) -- works
deriving instance Generic a => Generic (Y a) -- panic
deriving instance Generic (Y a) -- panic
data Z a = Z a
deriving instance Generic a => Generic (Z a) -- works
deriving instance Generic (Z a) -- works
}}}
I created a custom GHC API client to get a backtrace from the panic, but
that doesn't seem particularly helpful:
{{{
*** Exception (reporting due to +RTS -xc): (THUNK_2_0), stack trace:
TcInteract.solve_loop,
called from TcInteract.solveInteract,
called from TcRnDriver.simplifyTop,
called from TcRnDriver.tcRnSrcDecls,
called from HscMain.Typecheck-Rename,
called from Main.main,
called from Main.CAF
Segmentation fault
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5884#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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