#15012: "Iface type variable out of scope" when compiling with -c -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.1 Resolution: | Keywords: deriving Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4602 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => patch * differential: => Phab:D4602 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15012#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15012: "Iface type variable out of scope" when compiling with -c -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: patch Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.1 Resolution: | Keywords: deriving Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4602 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"b08a6d75e0440f33260bea5319b8c3f871b42f6e/ghc" b08a6d75/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="b08a6d75e0440f33260bea5319b8c3f871b42f6e" Fix #15012 with a well-placed use of Any Previously, derived `Generic1` instances could have associated `Rep1` type family instances with unbound variables, such as in the following example: ```lang=haskell data T a = MkT (FakeOut a) deriving Generic1 type FakeOut a = Int ==> instance Generic1 T where type Rep1 T = ... (Rec0 (FakeOut a)) ``` Yikes! To avoid this, we simply map the last type variable in a derived `Generic1` instance to `Any`. Test Plan: make test TEST=T15012 Reviewers: bgamari Reviewed By: bgamari Subscribers: simonpj, thomie, carter GHC Trac Issues: #15012 Differential Revision: https://phabricator.haskell.org/D4602 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15012#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15012: "Iface type variable out of scope" when compiling with -c -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.1 Resolution: fixed | Keywords: deriving Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4602 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"257c13d86db0a9ed540287127fd1c79abacf857e/ghc" 257c13d8/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="257c13d86db0a9ed540287127fd1c79abacf857e" Lint types in newFamInst We weren't linting the types used in `newFamInst`, which might have been why #15012 went undiscovered for so long. Let's fix that. One has to be surprisingly careful with expanding type synonyms in `lintType`, since in the offending program (simplified): ```lang=haskell type FakeOut a = Int type family TF a type instance TF Int = FakeOut a ``` If one expands type synonyms, then `FakeOut a` will expand to `Int`, which masks the issue (that `a` is unbound). I added an extra Lint flag to configure whether type synonyms should be expanded or not in Lint, and disabled this when calling `lintTypes` from `newFamInst`. As evidence that this works, I ran it on the offending program from #15012, and voilà: ``` $ ghc3/inplace/bin/ghc-stage2 Bug.hs -dcore-lint [1 of 1] Compiling Foo ( Bug.hs, Bug.o ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.5.20180417 for x86_64-unknown-linux): Core Lint error <no location info>: warning: In the type ‘... (Rec0 (FakeOut b_a1Qt))))’ @ b_a1Qt is out of scope ``` Test Plan: make test TEST=T15057 Reviewers: simonpj, goldfire, bgamari Reviewed By: bgamari Subscribers: thomie, carter GHC Trac Issues: #15057 Differential Revision: https://phabricator.haskell.org/D4611 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15012#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler