failure.undeclared_propagation

A function or action can end with a failure that its fails list doesn't name.

Area 4, Failures; not declinable; the next step is usually the agent's.

Why Jadpo refuses it

fails lists exactly the failures that can leave a callable: everything a reject or an attempt in its body can produce, less what a match handles. Callers read the list to know what they must handle, and Jadpo checks that they handle each one. A failure missing from it would reach callers that never planned for it.

What it looks like

main.jadpo:

type Note = Text {}type RegistrationClosed = Failure {    kind: FailureKind.conflict}action register(note: Note) -> Note {    reject RegistrationClosed}

  |8 |     reject RegistrationClosed  |     ^^^^^^^^^^^^^^^^^^^^^^^^^ rejected here

(agent) at the end of the next: line means your coding agent can make the fix itself.

A failure passed on from a call with attempt is the same error, at the attempt:

main.jadpo:

type Note = Text {}type Refused = Failure {    kind: FailureKind.rejected}action child(note: Note) fails Refused -> Note {    reject Refused}action parent(note: Note) -> Note {    return attempt child(note)}

   |12 |     return attempt child(note)   |            ^^^^^^^^^^^^^^^^^^^ passed on here

How to fix it

If callers should get the failure, add it to fails, before the result type's ->:

action register(note: Note) fails RegistrationClosed -> Note {    ...}

Every caller of register now passes RegistrationClosed on with attempt or handles it in a match. A route that runs it answers with the failure's code and the status its kind gives, 409 for conflict.

If the failure comes from a call and the caller can carry on, match on the call and handle it there, so it never leaves:

    return match child(note) {        success(kept) -> kept        Refused -> note    }

When child refuses, parent returns the note it was given, and its fails list stays empty.

Related

• Saying what can fail: fails
• Passing a failure on: attempt
• Handling a failure in match
• failure.stale_declaration