[GHC] #9611: Suggest the cause of "No instance" errors involving multiple versions of a package
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Suppose I have packages A-1.0, A-1.1, and B-1.0 built against A-1.0, and A (both versions) defines a type T which B defines to be an instance of some class C. If I load A-1.1 and B-1.0 into ghci and try to use the C T instance I will get a "No instance for C T" error, because T refers to A-1.1:T and B only defines an instance for A-1.0:T. However, if I don't realize this is what's going on, the error will be quite confusing as B appears to define an instance C T. Or, A could define the class C, rather than the type T, with the same result. This is quite common nowadays because there is a newer version of transformers (0.4.1.0) than the one which ships with GHC (0.3.0.0) and it's easy to end up installing mtl or lens against 0.3.0.0, and then some other package which pulls in 0.4.1.0. It would be nice to give a hint about what is going on, like {{{ No instance for (MonadIO X) arising from a use of ‘liftIO’ In the expression: ... ... Note: there is an instance transformers-0.3.0.0:MonadIO X }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.8.3 Component: Compiler | 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: | -------------------------------------+------------------------------------- Comment (by simonpj): I expect this would be do-able (look in `TcErrors`), but it'd mean implementing a variant of the instance-matching code, to look for a match "by name" (where `p1:A.B.T` matches `p2:A.B.T`) rather than "by identity" where those two types are simply different. I can offer guidance if someone tackles this. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by dmwit): * cc: me@… (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Yuras Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by Yuras): * owner: => Yuras Comment: I'll try to implement it unless someone already is on it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Yuras Type: feature request | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1919 Wiki Page: | -------------------------------------+------------------------------------- Changes (by Yuras): * status: new => patch * differential: => Phab:D1919 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9611: Suggest the cause of "No instance" errors involving multiple versions of a
package
-------------------------------------+-------------------------------------
Reporter: rwbarton | Owner: Yuras
Type: feature request | Status: patch
Priority: normal | Milestone:
Component: Compiler | Version: 7.8.3
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D1919
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Ben Gamari
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Yuras Type: feature request | Status: merge Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1919 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => merge * failure: None/Unknown => Incorrect warning at compile-time * milestone: => 8.0.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#9611: Suggest the cause of "No instance" errors involving multiple versions of a
package
-------------------------------------+-------------------------------------
Reporter: rwbarton | Owner: Yuras
Type: feature request | Status: merge
Priority: normal | Milestone: 8.0.1
Component: Compiler | Version: 7.8.3
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect | Unknown/Multiple
warning at compile-time | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D1919
Wiki Page: |
-------------------------------------+-------------------------------------
Comment (by Simon Peyton Jones
#9611: Suggest the cause of "No instance" errors involving multiple versions of a package -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Yuras Type: feature request | Status: closed Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.8.3 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1919 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed Comment: Merged to `ghc-8.0` a938c7ad62ccdd6ff4ea15df5ae2ddb8050a04df. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9611#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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