dckc
a9750957cd
Every failure path leaves a trace in the logs, and no failure is invented without checking what the API actually returns. Prompted by diigo-cache's password-manager save reporting "not saved" on success (CredentialsContainer.store() resolves with undefined). Generated-by: Claude Opus 5.5
37 lines
2.0 KiB
Markdown
37 lines
2.0 KiB
Markdown
---
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name: silent-failures-are-evil
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description: No silent failures — use when writing or reviewing error handling: catch blocks, promise rejections, fallbacks for unsupported features, or any branch that treats a result as "didn't work"; when a UI shows a failure with nothing logged; when someone says "silent failure". Every failure path leaves a trace in the logs, and no failure is invented without checking what the API actually returns.
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---
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# Silent failures are evil
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A failure nobody can see is a failure nobody can fix. Every failure path
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must leave a trace.
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## the rules
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- **Log every failure path**: a caught exception, a rejected promise, a
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falsy result treated as "didn't work", an unsupported-feature
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fallback. Changing a label on screen is not enough — log it, with an
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`event` tag for grepping, and no secrets (no keys, cookies, header or
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param values).
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- **Don't invent failures.** Before branching on a result, check what
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the API actually returns (the spec or MDN, not a guess). A success
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misreported as failure is as bad as a failure reported as nothing.
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- **Say only what you know.** When an API can't tell you the outcome,
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report what it did tell you ("offered", not "saved").
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- **Make it testable.** Pass the logger in (see
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[ocap-discipline](../ocap-discipline/SKILL.md)) so a test can assert
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that the failure path logged; a discovered silent failure is a goof
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that owes a test ([lazy-tdd](../lazy-tdd/SKILL.md)).
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## the goof that prompted this
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diigo-cache's password-manager save button said "not saved", with
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nothing in the console. The code read `c ? "saved" : "not saved"` on the
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result of [`CredentialsContainer.store()`](https://developer.mozilla.org/en-US/docs/Web/API/CredentialsContainer/store),
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which resolves with `undefined` per spec — even on success. So every
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save was reported as a failure, silently. The fix
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(`capsite/diigo-cache/src/pm-save.ts`) reports "offered", logs every
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outcome, and is covered by `tests/pm-save.test.ts`.
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