Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

• 7641a74a
  by Simon Peyton Jones at 2025-04-26T22:05:19-04:00

  Get a decent MatchContext for pattern synonym bindings
  
  In particular when we have a pattern binding
      K p1 .. pn = rhs
  where K is a pattern synonym.  (It might be nested.)
  
  This small MR fixes #25995.  It's a tiny fix, to an error message,
  removing an always-dubious `unkSkol`.
  
  The bug report was in the context of horde-ad, a big program,
  and I didn't manage to make a small repro case quickly. I decided
  not to bother further.
  

1 changed file:

• compiler/GHC/Tc/Gen/Pat.hs

Changes:

         ; let all_arg_tys = ty : prov_theta ++ (map scaledThing arg_tys)

         ; checkGADT (PatSynCon pat_syn) ex_tvs all_arg_tys penv

-        ; skol_info <- case pe_ctxt penv of

-                            LamPat mc -> mkSkolemInfo (PatSkol (PatSynCon pat_syn) mc)

-                            LetPat {} -> return unkSkol -- Doesn't matter

+        ; let match_ctxt = case pe_ctxt penv of

+                            LamPat mc -> mc

+                            LetPat {} -> PatBindRhs

+        ; skol_info <- mkSkolemInfo (PatSkol (PatSynCon pat_syn) match_ctxt)

         ; (tenv, ex_tvs') <- tcInstSuperSkolTyVarsX skol_info subst ex_tvs

            -- This freshens: Note [Freshen existentials]