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Simon Peyton Jones authored
This patch fixes Trac #15558. There turned out to be two distinct problems * In TcExpr.tc_poly_expr_nc we had tc_poly_expr_nc (L loc expr) res_ty = do { traceTc "tcPolyExprNC" (ppr res_ty) ; (wrap, expr') <- tcSkolemiseET GenSigCtxt res_ty $ \ res_ty -> setSrcSpan loc $ -- NB: setSrcSpan *after* skolemising, -- so we get better skolem locations tcExpr expr res_ty Putting the setSrcSpan inside the tcSkolemise means that the location on the Implication constraint is the /call/ to the function rather than the /argument/ to the call, and that is really quite wrong. I don't know what Richard's comment NB means -- I moved the setSrcSpan outside, and the "binding site" info in error messages actually improved. The reason I found this is that it affects the span reported for Trac #15558. * In TcErrors.mkGivenErrorReporter we carefully munge the location for an insoluble Given constraint (Note [Inaccessible code]). But the 'implic' passed in wasn't necesarily the immediately- enclosing implication -- but for location-munging purposes it jolly well should be. Solution: use the innermost implication. This actually simplifies the code -- no need to pass an implication in to mkGivenErrorReporter.
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