Saturate runtime cost accumulation to prevent overflow - #1449
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CostTracker.Observe accumulated call costs with an unchecked +=, so an overload reporting an unbounded actual cost wrapped the running total back to a small value whenever any cost had already accrued. json.encode, which reports math.MaxUint64, evaluated to a cost of 0 for json.encode(v) and 1 for json.encode(v) == json.encode(v). Only the all-constant case, where nothing has accrued yet, produced the intended cost. A wrapped total silently defeats CostTrackerLimit: json.encode(v) evaluated without error under a limit of 1000. Accumulate with cost.SafeAdd instead, matching the saturating convention documented throughout the cost package. The qualifier, ident and constructor increments are saturated as well, since those otherwise wrap an already saturated total back down to zero. TestEncodersCosts/json_encode_dyn asserted an unbounded estimated cost alongside an actual cost of 1, which was the wrapped value; it now expects math.MaxUint64.
TristonianJones
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jnthntatum
August 28, 2026 22:46
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CostTracker.Observeaccumulated call costs with an unchecked +=, so the code was switched tocost.SafeAddto preserve saturation.