Richard I'm on a train, so can't look at the detail. But the following thought occurs to me.
uo_thing is a Maybe SDoc attached to a constraint. But a constraint also has a stack of [ErrCtxt], captured in the CtLoc. That's what produces the "In the declaration for ..." stuff. Idea: instead of uo_thing, could we just push an extra ErrCtxt onto the stack, in the CtLoc for this constraint? (Or not, in the Nothing case.) Simon From: nore...@phabricator.haskell.org [mailto:nore...@phabricator.haskell.org] Sent: 18 July 2017 19:39 To: Simon Peyton Jones <simo...@microsoft.com> Subject: [Differential] [Request, 533 lines] D3754: Refactor uo_thing goldfire created this revision. Herald added subscribers: thomie, rwbarton. Herald added a reviewer: hvr. View Revision<https://phabricator.haskell.org/D3754> REVISION SUMMARY The uo_thing field of TypeEqOrigin is used to track the "thing" (either term or type) that has the type (kind) stored in the TypeEqOrigin fields. Previously, this was sometimes a proper Core Type, which needed zonking and tidying. Now, it is only HsSyn: much simpler, and the error messages now use the user-written syntax. But this aspect of uo_thing didn't cause Trac #13819<https://ghc.haskell.org/trac/ghc/ticket/13819>; it was the sibling field uo_arity that did. uo_arity stored the number of arguments of uo_thing, useful when reporting something like "should have written 2 fewer arguments". We wouldn't want to say that if the thing didn't have two arguments. However, in practice, GHC was getting this wrong, and this message didn't seem all that helpful. Furthermore, the calculation of the number of arguments is what caused Trac #13819<https://ghc.haskell.org/trac/ghc/ticket/13819> to fall over. This patch just removes uo_arity. In my opinion, the change to error messages is a nudge in the right direction. Test case: typecheck/should_fail/T13819 TEST PLAN ./validate REPOSITORY rGHC Glasgow Haskell Compiler BRANCH wip/rae REVISION DETAIL https://phabricator.haskell.org/D3754 AFFECTED FILES compiler/ghci/RtClosureInspect.hs compiler/typecheck/Inst.hs compiler/typecheck/TcArrows.hs compiler/typecheck/TcErrors.hs compiler/typecheck/TcExpr.hs compiler/typecheck/TcHsType.hs compiler/typecheck/TcMType.hs compiler/typecheck/TcPat.hs compiler/typecheck/TcRnTypes.hs compiler/typecheck/TcSigs.hs compiler/typecheck/TcSplice.hs compiler/typecheck/TcSplice.hs-boot compiler/typecheck/TcTyClsDecls.hs compiler/typecheck/TcType.hs compiler/typecheck/TcUnify.hs compiler/typecheck/TcUnify.hs-boot compiler/types/Type.hs testsuite/tests/indexed-types/should_fail/T12867.stderr testsuite/tests/polykinds/T12593.stderr testsuite/tests/polykinds/T6039.stderr testsuite/tests/polykinds/T7278.stderr testsuite/tests/polykinds/T8616.stderr testsuite/tests/polykinds/T9200b.stderr testsuite/tests/rename/should_fail/rnfail026.stderr testsuite/tests/th/T3177a.stderr testsuite/tests/typecheck/should_fail/T11356.stderr testsuite/tests/typecheck/should_fail/T11672.stderr testsuite/tests/typecheck/should_fail/T12785b.stderr testsuite/tests/typecheck/should_fail/T13819.hs testsuite/tests/typecheck/should_fail/T13819.stderr testsuite/tests/typecheck/should_fail/T2994.stderr testsuite/tests/typecheck/should_fail/T3540.stderr testsuite/tests/typecheck/should_fail/T4875.stderr testsuite/tests/typecheck/should_fail/T7609.stderr testsuite/tests/typecheck/should_fail/T7778.stderr testsuite/tests/typecheck/should_fail/all.T testsuite/tests/typecheck/should_fail/tcfail070.stderr testsuite/tests/typecheck/should_fail/tcfail078.stderr testsuite/tests/typecheck/should_fail/tcfail113.stderr testsuite/tests/typecheck/should_fail/tcfail123.stderr testsuite/tests/typecheck/should_fail/tcfail132.stderr EMAIL PREFERENCES https://phabricator.haskell.org/settings/panel/emailpreferences/ To: goldfire, simonpj, austin, bgamari, hvr Cc: rwbarton, thomie, Mikolaj, fryguybob, carter, mpickering, adamgundry
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