[GHC] #8978: Type synonyms are not *exactly* synonyms
#8978: Type synonyms are not *exactly* synonyms ----------------------------+---------------------------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects valid program Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ----------------------------+---------------------------------------------- {{{ {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeFamilies #-} type Syn a = Associated a class Eq (Associated a) => Foo a where type Associated a :: * foo :: a -> Syn a -> Bool instance Foo () where type Associated () = Int foo _ x = x == x }}} In 7.6.3 and 7.8.1-rc2, this file compiles. In 7.8.1 release, GHC produces this error: {{{ No instance for (Eq (Syn ())) arising from a use of ‘==’ In the expression: x == x In an equation for ‘foo’: foo _ x = x == x In the instance declaration for ‘Foo ()’ }}} even though there is an Eq instance for Associated (), and Syn is just a type synonym. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Changes (by goldfire): * cc: eir@… (added) Comment: I just got bit by this, too, on code that worked with 7.8.1 RC2. A perusal through a `-ddump-tc-trace` makes it look like something in the constraint solver, but I could be wrong. An easy workaround (if you wrote the type synonym) is to use a one- equation type family instead. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by goldfire): Could this be from 6ae678e31a5fdd3b0bd1f8613fe164012bb630f4? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Changes (by Lemming): * cc: ghc@… (added) Comment: You can find another example in #8979. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by Lemming): Replying to [comment:2 goldfire]:
An easy workaround (if you wrote the type synonym) is to use a one- equation type family instead.
That helped. Thanks for the suggestion! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by joelteon): The single-equation solution fixes this particular problem, but this is a simplification of library code that's throwing this error now, in which the type family cannot be closed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by goldfire): Sorry if I was unclear -- I meant to change the vanilla type synonym into a type family. My guess is that GHC won't care whether the new family is closed or open with one universal equation (if you need backward compatibility). You don't need to change the existing type family for my workaround. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by simonpj): Ugh. This is my fault; an egregious blunder in a (cool) clean-up of the type flattener. It's easy to fix (patch coming) but the bug is in the released 7.8.1. Will fix in 7.8.2. It just shows, you never have enough regression tests! It affects any type synonym whose RHS mentions a type family. (Data families are fine.) Such as `Syn` above, or `H` in #8979. Richard's workaround is good; use a type family instead. Sorry about this. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by Lemming): Replying to [comment:8 simonpj]:
Ugh. This is my fault; an egregious blunder in a (cool) clean-up of the type flattener. It's easy to fix (patch coming) but the bug is in the released 7.8.1. Will fix in 7.8.2. It just shows, you never have enough regression tests!
Will there be a "nightly snapshot build" for easy testing of the bugfix? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by snoyberg): This bug has apparently broken a number of my packages, and I'm not certain if all of them can be fixed in a way that's backwards compatible with GHC 7.4 and 7.6 (both of which I still support). Would it be possible to release 7.8.2 with this fix alone, instead of waiting a number of months for the release as would normally be done? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely
----------------------------------------------+----------------------------
Reporter: joelteon | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.8.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: GHC rejects valid program | Unknown/Multiple
Test Case: | Difficulty: Unknown
Blocking: | Blocked By:
| Related Tickets:
----------------------------------------------+----------------------------
Comment (by Simon Peyton Jones
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by simonpj): Yes, I'm afraid that if I really have broken a number of significant packages since RC2, we probably should make a quick 7.8.2. Who else has come across this? Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by snoyberg): Thanks Simon. I'll be happy to do any testing of such a release. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:13 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: new Priority: highest | Milestone: 7.8.2 Component: Compiler | Version: 7.8.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Changes (by hvr): * priority: normal => highest * milestone: => 7.8.2 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: closed Priority: highest | Milestone: 7.8.2 Component: Compiler | Version: 7.8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Changes (by thoughtpolice): * status: new => closed * resolution: => fixed Comment: Merged in 7.8, thanks Simon. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: closed Priority: highest | Milestone: 7.8.2 Component: Compiler | Version: 7.8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by Lemming): Replying to [comment:12 simonpj]:
Who else has come across this?
I encountered the bug when working on the tfp package. I could fix one problem within the package using the one-equation type family work-around. But the bug also affected the dependending llvm-tf package at several places. Thus I stopped working around and this means, that there might be more yet unseen places where it causes problems. Before a new release I would like very much to get a "nightly snapshot build" or "release candidate" for testing on 64-bit Linux. Otherwise I am afraid that the bugfix causes other subtle problems that will be part of 7.8.2. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:16 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: closed Priority: highest | Milestone: 7.8.2 Component: Compiler | Version: 7.8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by simonpj): The fix is merged on the 7.8.2 branch, so you can build it and try. I don't know if anyone has a pre-built binary distribution for your platform though. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
The fix is merged on the 7.8.2 branch, so you can build it and try. I don't know if anyone has a pre-built binary distribution for your platform
#8978: Type synonyms in class associated types behave strangely ----------------------------------------------+---------------------------- Reporter: joelteon | Owner: Type: bug | Status: closed Priority: highest | Milestone: 7.8.2 Component: Compiler | Version: 7.8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by Lemming): Replying to [comment:17 simonpj]: though. I can confirm that the problems are gone with the ghc-7.8.1.20140410 built by Michael Snoyman. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:18 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#8978: Type synonyms in class associated types behave strangely -------------------------------------------------+------------------------- Reporter: joelteon | Owner: Type: bug | Status: Priority: highest | closed Component: Compiler | Milestone: 7.8.2 Resolution: fixed | Version: 7.8.1 Operating System: Unknown/Multiple | Keywords: Type of failure: GHC rejects valid program | Architecture: Test Case: indexed- | Unknown/Multiple types/should_compile/T8978 | Difficulty: Blocking: | Unknown | Blocked By: | Related Tickets: -------------------------------------------------+------------------------- Changes (by simonpj): * testcase: => indexed-types/should_compile/T8978 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8978#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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