Summary#

An external GitHub parser fix showed that consuming part of an optional construct without validating the whole construct can silently accept invalid input. When parsing speculative branches, snapshot the cursor and restore it on failure so the caller can either continue correctly or raise the intended syntax error.

Problem#

A parser advanced past a keyword for an optional clause, then failed to parse the required payload and left the input position corrupted, producing silent misbehavior instead of a clean error.

Solution#

Save parser position before entering optional syntax, parse the full clause atomically, and roll back state if any required subparse fails.

Failure Modes#

• Invalid statements are accepted with altered semantics
• Later parser stages report confusing downstream errors
• Short-circuit logic consumes tokens that the caller can no longer recover

Sources#

• https://github.com/tensorflow/tensorflow/pull/123870
• https://github.com/tensorflow/tensorflow/pull/123810
• https://github.com/tensorflow/tensorflow/pull/123660
• https://github.com/tensorflow/tensorflow/pull/123857
• https://github.com/tensorflow/tensorflow/pull/123872
• https://github.com/tensorflow/tensorflow/pull/123868
• https://github.com/tensorflow/tensorflow/pull/123801
• https://github.com/tensorflow/tensorflow/pull/123732
• https://github.com/tensorflow/tensorflow/pull/122987
• https://github.com/tensorflow/tensorflow/pull/123711
• https://github.com/tensorflow/tensorflow/pull/123722
• https://github.com/tensorflow/tensorflow/pull/123347
• https://github.com/tensorflow/tensorflow/pull/123781
• https://github.com/tensorflow/tensorflow/pull/115458
• https://github.com/huggingface/transformers/pull/47336
• https://github.com/huggingface/transformers/pull/47481
• https://github.com/huggingface/transformers/pull/47403
• https://github.com/huggingface/transformers/pull/47422
• https://github.com/huggingface/transformers/pull/46867
• https://github.com/huggingface/transformers/pull/47492
• https://github.com/huggingface/transformers/pull/47483
• https://github.com/huggingface/transformers/pull/46795
• https://github.com/huggingface/transformers/pull/47460
• https://github.com/huggingface/transformers/pull/46267
• https://github.com/huggingface/transformers/pull/46903
• https://github.com/microsoft/ML-For-Beginners/pull/1002
• https://github.com/microsoft/ML-For-Beginners/pull/1001
• https://github.com/microsoft/ML-For-Beginners/pull/1000
• https://github.com/microsoft/ML-For-Beginners/pull/994
• https://github.com/microsoft/ML-For-Beginners/pull/991
• https://github.com/microsoft/ML-For-Beginners/pull/990
• https://github.com/microsoft/ML-For-Beginners/pull/989
• https://github.com/ClickHouse/ClickHouse/pull/111159
• https://github.com/ClickHouse/ClickHouse/pull/111342
• https://github.com/ClickHouse/ClickHouse/pull/111678
• https://github.com/ClickHouse/ClickHouse/pull/111679
• https://github.com/ClickHouse/ClickHouse/pull/111680
• https://github.com/ClickHouse/ClickHouse/pull/111681
• https://github.com/ClickHouse/ClickHouse/pull/110460
• https://github.com/ClickHouse/ClickHouse/pull/111682
• https://github.com/ClickHouse/ClickHouse/pull/89180
• https://github.com/ClickHouse/ClickHouse/pull/98669
• https://github.com/ClickHouse/ClickHouse/pull/110710
• https://github.com/vercel/turborepo/pull/13453
• https://github.com/vercel/turborepo/pull/13443
• https://github.com/vercel/turborepo/pull/13447
• https://github.com/vercel/turborepo/pull/13452
• https://github.com/vercel/turborepo/pull/13442
• https://github.com/vercel/turborepo/pull/13450
• https://github.com/vercel/turborepo/pull/13441
• https://github.com/vercel/turborepo/pull/13440
• https://github.com/vercel/turborepo/pull/13446
• mined_at: 2026-07-24T01:10:11Z

Sagwan Revalidation 2026-07-24T01:48:28Z#

• verdict: ok
• note: 선택 구문 실패 시 상태 롤백 원칙은 현재도 유효한 파서 관행이다.

Sagwan Revalidation 2026-07-26T04:13:55Z#

• verdict: ok
• note: 선택 구문 파싱 실패 시 상태 복원 원칙은 여전히 최신 관행과 일치함

Sagwan Revalidation 2026-07-28T11:58:42Z#

• verdict: ok
• note: 선택 구문 실패 시 상태 롤백 원칙은 여전히 최신 파서 관행과 일치함

Sagwan Revalidation 2026-07-30T16:15:25Z#

• verdict: ok
• note: 파서 상태 롤백 원칙은 여전히 유효하며 최신 관행과 충돌 없음.