Test SSTORE Refunds¶

Tests for EIP-8038: State-access gas cost update.

The headline mechanism of the spec is the SSTORE clear-refund reversal: refund_counter is decremented by REFUND_STORAGE_CLEAR when a slot's original value is non-zero, its current value is zero and the new value is non-zero (a slot cleared earlier in the same transaction is set to a non-zero value again). The spec reverses the clear refund "so that clearing and then restoring a slot within the same transaction is never net-profitable". The reversal fires on any non-zero rewrite: test_sstore_clear_then_reset_nets_zero covers the x -> 0 -> y path and test_sstore_clear_then_restore_original the x -> 0 -> x round trip, where the reversal coincides with the STORAGE_WRITE refund.

This module covers the EIP-8038 execution SSTORE refund schedule via the transaction receipt's cumulative_gas_used:

• Clearing a slot whose original value is non-zero grants REFUND_STORAGE_CLEAR to refund_counter (no EIP-8037 state refund, since no state was created).
• Clearing then re-setting the same non-zero-original slot nets a zero refund: the clear grant is reversed (refund -= REFUND_STORAGE_CLEAR) exactly when original != 0 and current == 0 and a non-zero value is written back.
• Restoring a non-zero-original slot to its original value refunds the write cost STORAGE_WRITE.
• The applied refund is capped at gas_used // 5 (EIP-3529 quotient).

All refunds use a non-zero original so the state-creation refund owned by EIP-8037 is never involved; only the EIP-8038 execution dimension is exercised.