[GHC] #8550: GHC builds recursive coerctions when using recursive type families
#8550: GHC builds recursive coerctions when using recursive type families -------------------------------------------+------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- Consider {{{ {-# LANGUAGE TypeFamilies, GADTs, UndecidableInstances #-} type family F a type instance F () = F () data A where A :: F () ~ () => A x :: A x = A }}} On GHC 7.6.3 it yields a context reduction stack overflow (despite F () ~ () being put into the “solved funeqs” list). In HEAD, a recursive dictionary is built, but then detected: {{{ [1 of 1] Compiling Foo ( Foo.hs, Foo.o ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.7.20131108 for x86_64-unknown-linux): Cycle in coercion bindings [[cobox_ayX{v} [lid] = CO main:Foo.TFCo:R:F(){tc rob}[0] ; cobox_ayZ{v} [lid], cobox_ayZ{v} [lid] = CO cobox_ayX{v} [lid] ; cobox_az0{v} [lid]]] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Either this panic needs to be turned into an error, or we need to prevent recursive dictionaries for when solving funeqs (similar to how we do it for `Coercible`). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families --------------------------------------------+------------------------------ Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Changes (by nomeata): * version: 7.6.3 => -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families --------------------------------------------+------------------------------ Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by monoidal): Could you check whether it works now? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families --------------------------------------------+------------------------------ Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by nomeata): Yes, same thing. What would make you think it changed since two weeks ago? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families --------------------------------------------+------------------------------ Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by monoidal): Sorry, I couldn't reproduce; now I see the panic needs compiling with DEBUG. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families --------------------------------------------+------------------------------ Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by nomeata): Ah, ok. Did not try that. What happens when you actually run the code? I assume it will just loop... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families --------------------------------------------+------------------------------ Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by monoidal): Right. `main = seq A (return ())` loops. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: (Type checker) | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Changes (by thomie): * priority: normal => high * milestone: => 7.10.1 Old description:
Consider {{{ {-# LANGUAGE TypeFamilies, GADTs, UndecidableInstances #-} type family F a type instance F () = F () data A where A :: F () ~ () => A x :: A x = A }}}
On GHC 7.6.3 it yields a context reduction stack overflow (despite F () ~ () being put into the “solved funeqs” list).
In HEAD, a recursive dictionary is built, but then detected: {{{ [1 of 1] Compiling Foo ( Foo.hs, Foo.o ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.7.20131108 for x86_64-unknown-linux): Cycle in coercion bindings [[cobox_ayX{v} [lid] = CO main:Foo.TFCo:R:F(){tc rob}[0] ; cobox_ayZ{v} [lid], cobox_ayZ{v} [lid] = CO cobox_ayX{v} [lid] ; cobox_az0{v} [lid]]]
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}}
Either this panic needs to be turned into an error, or we need to prevent recursive dictionaries for when solving funeqs (similar to how we do it for `Coercible`).
New description: Consider {{{ {-# LANGUAGE TypeFamilies, GADTs, UndecidableInstances #-} type family F a type instance F () = F () data A where A :: F () ~ () => A x :: A x = A main = seq A (return ()) }}} On GHC 7.6.3 it yields a context reduction stack overflow (despite F () ~ () being put into the “solved funeqs” list). In HEAD, a recursive dictionary is built, but then detected: {{{ [1 of 1] Compiling Foo ( Foo.hs, Foo.o ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.7.20131108 for x86_64-unknown-linux): Cycle in coercion bindings [[cobox_ayX{v} [lid] = CO main:Foo.TFCo:R:F(){tc rob}[0] ; cobox_ayZ{v} [lid], cobox_ayZ{v} [lid] = CO cobox_ayX{v} [lid] ; cobox_az0{v} [lid]]] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Either this panic needs to be turned into an error, or we need to prevent recursive dictionaries for when solving funeqs (similar to how we do it for `Coercible`). -- Comment: Trying to compile the example from the description with ghc-7.9.20141115 results in GHC using lots of memory, making my machine unusable until I kill the process. This seems like a regression, setting priority to high. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler (Type | Version: checker) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by simonpj): * cc: goldfire (added) Comment: Richard any comments? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler (Type | Version: checker) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #7788 | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * related: => #7788 Comment: This looks like a duplicate of #7788. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8550: GHC builds recursive coerctions when using recursive type families
-------------------------------------+-------------------------------------
Reporter: nomeata | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.12.1
Component: Compiler (Type | Version:
checker) | Keywords:
Resolution: | Architecture:
Operating System: Unknown/Multiple | Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: #7788 | Differential Revisions:
-------------------------------------+-------------------------------------
Comment (by Richard Eisenberg
#8550: GHC builds recursive coerctions when using recursive type families -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: closed Priority: high | Milestone: 7.12.1 Component: Compiler (Type | Version: checker) | Keywords: Resolution: fixed | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: None/Unknown | Test Case: indexed- Blocked By: | types/should_fail/T8550 Related Tickets: #7788 | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by goldfire): * status: new => closed * testcase: => indexed-types/should_fail/T8550 * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8550#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
participants (1)
-
GHC