[GHC] #14848: -XDuplicateRecordFields breaks record expression splices
#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: GHC rejects (amd64) | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ {-# language TemplateHaskell #-} {-# language DuplicateRecordFields #-} module Lib where import Language.Haskell.TH import Language.Haskell.TH.Syntax data A = A {x :: Int, y :: String} a = A 3 "test" test = $([e|case a of A {x = b} -> b|]) }}} Without `DuplicateRecordFields` it compiles correctly so `test = 3` but with `DuplicateRecordFields` enabled it gives: {{{ • Illegal variable name: ‘$sel:x:A’ When splicing a TH expression: case Lib.a of (Lib.A {Lib.$sel:x:A = b_0}) -> b_0 • In the untyped splice: $([| case a of { A {x = b} -> b } |]) }}} Additionally, there doesn't seem to be a workaround for munging the name manually, since the `$sel:x:A` name is the one actually in scope, there is no `A.x` like there would be normally, even when the label is not a duplicate. Is there a way to get around this? Ex: by changing the binding name somehow manually? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14848 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: ORF Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => ORF -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14848#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: ORF Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by adamgundry): * cc: adamgundry (added) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14848#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: ORF Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by adamgundry): I think a possible fix here is to apply the approach described in `Note [Reifying field labels] from TcSplice` in the `HsRecFld` case of `DsMeta.repE`. That is, rather than representing the field as a `NameG` containing the mangled selector name (which isn't a legal variable name, let alone in scope), we could represent it as a `NameQ` containing the field label. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14848#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: ORF Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: #11103 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by adamgundry): * related: => #11103 Comment: I've just rediscovered this issue, and the interaction between `DuplicateRecordFields` and `TemplateHaskell` definitely needs to be addressed more carefully. The problem here is the case for `HsRecFld` in `DsMeta.repE`, which simply replaces the field occurrence with the selector function (which has an internal name that cannot be spliced in, namely `Name "$sel:x:A" (NameG VarName pkg "Lib")`). There are other related problems in `DsMeta` for representing fields in record definition, construction and pattern matching. The way #11103 dealt with a similar problem in reification was to represent field names using a specially-crafted `NameQ`, rather than a `NameG`. In this example that approach would give `Name "x" (NameQ "Lib")` instead. Note that `NameG` cannot be used with the field label in place of the selector, because that leads to looking up an Orig name that doesn't exist. However, while using `NameQ` should fix this example, it doesn't work in general: it means the name is dynamically bound, but of course the field might not be in scope when the splice is run. For a concrete example of this, consider a tiny variant of the test case from #12993: {{{#!hs {-# LANGUAGE DuplicateRecordFields #-} {-# LANGUAGE TemplateHaskell #-} module T12993_Lib (q) where data X = X { x :: Int } q = [|x|] }}} {{{#!hs {-# LANGUAGE TemplateHaskell #-} module T12993 where import T12993_Lib f = $(q) }}} This currently fails with an "Illegal variable name" error similar to the original report from this ticket. With the `NameQ` approach, it would still fail because `x` is not in scope in `T12993`. It seems fairly clear to me that dealing with this properly requires extending the TH AST in some way. The least invasive option might be to extend `NameFlavour` with a new constructor for field names, which would be rather like `NameG` but would carry the selector name. I'm not sure if there are better designs, however. What is the process for proposing/discussing such changes to TH? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14848#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#14848: -XDuplicateRecordFields breaks record expression splices -------------------------------------+------------------------------------- Reporter: dailectic | Owner: adamgundry Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Resolution: | Keywords: ORF Operating System: Linux | Architecture: x86_64 Type of failure: GHC rejects | (amd64) valid program | Test Case: Blocked By: | Blocking: Related Tickets: #11103 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by adamgundry): * owner: (none) => adamgundry Comment:
The least invasive option might be to extend `NameFlavour` with a new constructor for field names, which would be rather like `NameG` but would carry the selector name.
I've tried this, and it looks like a relatively straightforward change (although we may need an equivalent to `NameL` as well, I'm not sure yet). Will propose a patch. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14848#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
participants (1)
-
GHC