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fix: replace Fun.protect in transact with backtrace-free variant - #33
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On Melange targets the stdlib Fun.protect re-raises the work exception through primitives that are not polyfilled, so an exception inside a transaction surfaced as "caml_restore_raw_backtrace not polyfilled" instead of the real error. Use a local equivalent that keeps the same finally/exception semantics minus backtrace preservation.
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I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".
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tiensonqin
marked this pull request as ready for review
October 4, 2026 10:52
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Summary
impl/transact.mlwraps each transaction inFun.protect ~finally:restore_memo. On Melange targets,Fun.protectre-raises the work exception throughPrintexc.raise_with_backtrace→caml_restore_raw_backtrace, which is not polyfilled — so any exception thrown inside a transaction (e.g. a schema-validation failure) surfaced as"caml_restore_raw_backtrace not polyfilled by Melange yet", masking the real error entirely.Replace it with a local
protectthat keeps identical semantics —finallyruns on both success and exception paths,Finally_raisedstill wraps a failingfinally— minus backtrace preservation. Native callers lose only the original raise-site backtrace, not the exception.Test coverage
Compiles clean (
dune build impl/). Behavior-only change on the exception path; no new tests.Link to Devin session: https://app.devin.ai/sessions/813c52cd0faf4c458fdb45ed456c0179
Open in Devin Desktop: https://app.devin.ai/desktop/session/813c52cd0faf4c458fdb45ed456c0179?variant=devin
Requested by: @tiensonqin