#13199: TH-spliced class instances are pretty-printed incorrectly post-#3384 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: alanz Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: | -------------------------------------+------------------------------------- Comment (by alanz): I think this is related to point 3 in the description of https://phabricator.haskell.org/D2752 Basically `HsParTy` appears everywhere it needs to in the `ParsedSource`, but it somehow disappears through the renamer. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13199#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13199: TH-spliced class instances are pretty-printed incorrectly post-#3384 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: alanz Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 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: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Ah, so GHC will only print parentheses around types is an explicit `HsParTy` is used? In that case, I believe I know what the real culprit is. If you dig down deep enough to the code that `runMetaD` is running, you'll eventually come to [http://git.haskell.org/ghc.git/blob/de78ee6fb77e7505160ab23e6e1b4e66dc87f698... the part] in `Convert` that coverts a Template Haskell `InstanceD` to a `ClsInstDecl`: {{{#!hs cvtDec (InstanceD o ctxt ty decs) = do { let doc = text "an instance declaration" ; (binds', sigs', fams', ats', adts') <- cvt_ci_decs doc decs ; unless (null fams') (failWith (mkBadDecMsg doc fams')) ; ctxt' <- cvtContext ctxt ; L loc ty' <- cvtType ty ; let inst_ty' = mkHsQualTy ctxt loc ctxt' $ L loc ty' ; returnJustL $ InstD $ ClsInstD $ ClsInstDecl { cid_poly_ty = mkLHsSigType inst_ty' , cid_binds = binds' , cid_sigs = Hs.mkClassOpSigs sigs' , cid_tyfam_insts = ats', cid_datafam_insts = adts' , cid_overlap_mode = fmap (L loc . overlap) o } } }}} In particular, if you trace the value of `ty'` when you run the program above, it'll give you `instance C a_a4m5 Maybe b_a4m6`. That's because the original Template Haskell AST for this is: {{{ λ> import Language.Haskell.TH λ> putStrLn $([d| instance C a (Maybe b) |] >>= stringE . show) [InstanceD Nothing [] (AppT (AppT (ConT Bug.C) (VarT a_6989586621679027494)) (AppT (ConT GHC.Base.Maybe) (VarT b_6989586621679027495))) []] }}} That is, there are no AST nodes to indicate parentheses. That's because when we originally quoted this declaration earlier, `repTy` (located [http://git.haskell.org/ghc.git/blob/de78ee6fb77e7505160ab23e6e1b4e66dc87f698... here] in `DsMeta`) turns the `HsType` into a Template Haskell `Type`. And `repTy` has this as one of its cases: {{{#!hs repTy (HsParTy t) = repLTy t }}} `repTy` strips away all parentheses, and this is by design, according to [http://git.haskell.org/ghc.git/blob/de78ee6fb77e7505160ab23e6e1b4e66dc87f698... /template-haskell/Language/Haskell/TH/Syntax.hs#l1441 this note]: {{{#!hs --- * Quoted expressions such as --- --- > [| a * b + c |] :: Q Exp --- > [p| a : b : c |] :: Q Pat --- > [t| T + T |] :: Q Type --- --- will never contain 'UInfixE', 'UInfixP', 'UInfixT', 'InfixT', 'ParensE', --- 'ParensP', or 'ParensT' constructors. }}} So I believe the proper fix here is //not// to make `repTy` turn an `HsParTy` into a `ParensT`, but rather to change `cvtType` so that it inserts `HsParTy`s appropriately as it converts from a TH AST back to an `HsType`, right? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13199#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13199: TH-spliced class instances are pretty-printed incorrectly post-#3384 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: alanz Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D3043 Wiki Page: | -------------------------------------+------------------------------------- Changes (by alanz): * status: new => closed * resolution: => fixed -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13199#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler