D3754: Refactor uo_thing

[Simon Peyton Jones]

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: noreply at phabricator.haskell.org [mailto:noreply at phabricator.haskell.org]
Sent: 18 July 2017 19:39
To: Simon Peyton Jones <simonpj at 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

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To: goldfire, simonpj, austin, bgamari, hvr
Cc: rwbarton, thomie, Mikolaj, fryguybob, carter, mpickering, adamgundry
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