starknet_api: fix compiler->SNAPI contract class ABI string conversion for tests

[dorimedini-starkware]

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[reviewable-StarkWare]

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[dorimedini-starkware]

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• starknet_os_flow_tests: change FlowTestTx to enum #9501
• starknet_os_flow_tests: migrate test_v1_bound_accounts_cairo1 #9496
• starknet_os_flow_tests: add V1-bound cairo1 account for flow tests #9495
• starknet_api: fix compiler->SNAPI contract class ABI string conversion for tests #9494 👈 (View in Graphite)
• starknet_os_flow_tests: migrate test_v1_bound_accounts_cairo0 #9493
• starknet_os_flow_tests: split get_class_info_of_cairo0_contract into function #9492
• starknet_os_flow_tests: more informative execution failure #9491
• starknet_os_flow_tests: add V1-bound cairo0 account for flow tests #9490
• starknet_os_flow_tests: localize expected storage updates in test_os_logic #9485
• starknet_os_flow_tests: migrate test_os_logic and some small refactors #9484
• blockifier_test_utils: add functionality to test contract for test_os_logic #9483
• blockifier_test_utils: add test_contract2 cairo0 contract #9482
• blockifier_test_utils: add delegate_proxy cairo0 contract #9481
• starknet_os_flow_tests: add control for expected reverting txs #9480
• starknet_os_flow_tests: migrate test_reverted_l1_handler_tx #9474
• starknet_os_flow_tests: migrate test_reverted_invoke_tx #9473
• starknet_os_flow_tests: reduce boilerplate with perform_default_validations #9472
• main

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[github-actions]

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• Started at 2025-10-05T07:46:05Z
• Started at 2025-10-05T07:52:33Z
• Started at 2025-10-05T09:15:44Z
• Started at 2025-10-05T09:16:39Z
• Started at 2025-10-05T09:38:40Z

[dorimedini-starkware]

Reviewable status: 0 of 4 files reviewed, all discussions resolved (waiting on @AvivYossef-starkware, @meship-starkware, and @Yoni-Starkware)

---

crates/starknet_api/src/state.rs line 324 at r1 (raw file):

                        .format_to_string(&abi)
                        .unwrap()
                })

without this change, the next PR fails the sanity check in test_v1_bound_accounts_cairo1.
@Yoni-Starkware FYI

Code quote:

            abi: cairo_lang_contract_class
                .abi
                .map(|abi| {
                    serde_json_fmt::JsonFormat::new()
                        .comma(", ")
                        .unwrap()
                        .colon(": ")
                        .unwrap()
                        .format_to_string(&abi)
                        .unwrap()
                })

[github-actions]

Benchmark movements: No major performance changes detected.

[dorimedini-starkware]

Reviewable status: 0 of 4 files reviewed, all discussions resolved (waiting on @AvivYossef-starkware, @meship-starkware, and @Yoni-Starkware)

---

crates/starknet_api/src/state.rs line 317 at r1 (raw file):

                .abi
                .map(|abi| {
                    serde_json_fmt::JsonFormat::new()

apparently, this crate adds smart-string which changes String under the hood... so I'll need to implement this formatter manually

Code quote:

serde_json_fmt::JsonFormat