fix: reject sym apply with an unresolved instance argument#14113
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fix: reject sym apply with an unresolved instance argument#14113sgraf812 wants to merge 1 commit into
sym apply with an unresolved instance argument#14113sgraf812 wants to merge 1 commit into
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`BackwardRule.apply` takes its subgoals from `mkResultPos`, which drops instance arguments on the assumption that type class resolution discharges them. When `trySynthInstance` fails for an instance argument and unification does not assign it, `mkPreResult` substitutes a fresh metavariable that is neither returned as a subgoal nor otherwise resolved, so the goal was closed with a proof carrying that metavariable. It surfaced later as a kernel unresolved-metavariable error. `apply` now checks, when handing out the subgoals, that every instance argument is assigned. An unassigned one makes the rule inapplicable.
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Lean.Meta.Sym.BackwardRule.applytakes its subgoals frommkResultPos, whichdrops instance arguments on the assumption that type class resolution discharges
them. When
trySynthInstancefails for an instance argument and unification doesnot assign it,
mkPreResultsubstitutes a fresh metavariable that is neitherreturned as a subgoal nor otherwise resolved. The goal was closed with a proof
carrying that metavariable, surfacing later as a kernel unresolved-metavariable
error.
applynow checks, when handing out the subgoals, that every instance argument isassigned (synthesized or unified). An unassigned one makes the rule inapplicable.
reports
`apply` failed, rule is not applicable.