#14441: GHC HEAD regression involving type families in kinds -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: TypeInType, | TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #13790 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: simonpj (added) Comment: This was introduced in commit 74cd1be0b2778ad99566cde085328bde2090294a (`Don't deeply expand insolubles`). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14441#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14441: GHC HEAD regression involving type families in kinds -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: TypeInType, | TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #13790 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): We have in play #12919, which completely rewrites the flattening code. It also fixes at least six other tickets: the current setup is outright wrong. So Richard and I propose to park this bug and return to it when #12919 is committed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14441#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14441: GHC HEAD regression involving type families in kinds -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: TypeInType, | TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: 12919 | Blocking: Related Tickets: #13790 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Richard Eisenberg ): In [changeset:"e3dbb44f53b2f9403d20d84e27f187062755a089/ghc" e3dbb44f/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="e3dbb44f53b2f9403d20d84e27f187062755a089" Fix #12919 by making the flattener homegeneous. This changes a key invariant of the flattener. Previously, flattening a type meant flattening its kind as well. But now, flattening is always homogeneous -- that is, the kind of the flattened type is the same as the kind of the input type. This is achieved by various wizardry in the TcFlatten.flatten_many function, as described in Note [flatten_many]. There are several knock-on effects, including some refactoring in the canonicalizer to take proper advantage of the flattener's changed behavior. In particular, the tyvar case of can_eq_nc' no longer needs to take casts into account. Another effect is that flattening a tyconapp might change it into a casted tyconapp. This might happen if the result kind of the tycon contains a variable, and that variable changes during flattening. Because the flattener is homogeneous, it tacks on a cast to keep the tyconapp kind the same. However, this is problematic when flattening CFunEqCans, which need to have an uncasted tyconapp on the LHS and must remain homogeneous. The solution is a more involved canCFunEqCan, described in Note [canCFunEqCan]. This patch fixes #13643 (as tested in typecheck/should_compile/T13643) and the panic in typecheck/should_compile/T13822 (as reported in #14024). Actually, there were two bugs in T13822: the first was just some incorrect logic in tryFill (part of the unflattener) -- also fixed in this patch -- and the other was the main bug fixed in this ticket. The changes in this patch exposed a long-standing flaw in OptCoercion, in that breaking apart an AppCo sometimes has unexpected effects on kinds. See new Note [EtaAppCo] in OptCoercion, which explains the problem and fix. Also here is a reversion of the major change in 09bf135ace55ce2572bf4168124d631e386c64bb, affecting ctEvCoercion. It turns out that making the flattener homogeneous changes the invariants on the algorithm, making the change in that patch no longer necessary. This patch also fixes: #14038 (dependent/should_compile/T14038) #13910 (dependent/should_compile/T13910) #13938 (dependent/should_compile/T13938) #14441 (typecheck/should_compile/T14441) #14556 (dependent/should_compile/T14556) #14720 (dependent/should_compile/T14720) #14749 (typecheck/should_compile/T14749) Sadly, this patch negatively affects performance of type-family- heavy code. The following patch fixes these performance degradations. However, the performance fixes are somewhat invasive and so I've kept them as a separate patch, labeling this one as [skip ci] so that validation doesn't fail on the performance cases. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14441#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler