# M4b task 04: an answer records its post; the table says what is pending

**Branch:** `m4b` (run `git switch m4b`; `git status --short` must be empty, otherwise stop)
**Commit subject:** `brokerd: answers carry the Mattermost post; Table::contains`

## Goal

When an approval is answered from Mattermost, the audit record must name the approver **and the
post** that answered (the `Approval` record has had a `post` field since M3a, always `None` so
far). And the courier (task 06) needs to ask the approval table whether an approval is still
pending.

`ledger.rs` is at 499 lines, so first `Answer` and `Answered` move to `approvals.rs`, beside
`Verdict` and `Entry`; `ledger` re-exports them, so every `crate::ledger::Answer` still works.

## Files

- Copy: `crates/brokerd/tests/ledger_post.rs`, and **new versions** of three given tests,
  `crates/brokerd/tests/broker_pending.rs`, `broker_sequence.rs` and `ledger_answer.rs` (the only
  change in each: `post: None,` in every `Answer::Approved` and `Answer::Refused`)
- Modify: `crates/brokerd/src/approvals.rs`, `crates/brokerd/src/ledger.rs`,
  `crates/brokerd/src/admin.rs`, `docs/implementer-log.md`

## The changes, exactly

**1. Move.** Cut `enum Answer` and `struct Answered` from `ledger.rs`, with their doc comments,
and paste them into `approvals.rs`, before `pub struct Entry`. In `ledger.rs`, add
`pub use crate::approvals::{Answer, Answered};` next to `use crate::approvals::Verdict;`. In
`approvals.rs`, `use proto::{DenyReason, PendingApproval, Timestamp};` becomes
`use proto::{DecisionRecord, DenyReason, PendingApproval, Timestamp};`.

**2. `post`.** In `approvals.rs`, `Answer` becomes:

```rust
/// An owner's answer to a pending call.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Answer {
    /// `by` is "bxctl" or a Mattermost user id; `post` the Mattermost post that answered.
    Approved {
        by: Option<String>,
        post: Option<String>,
    },
    Refused {
        by: Option<String>,
        post: Option<String>,
        reason: Option<String>,
    },
    Expired,
}
```

In `ledger.rs`, `answer`, step 3 becomes:

```rust
        let (answer, by, post, reason) = match &answer {
            Answer::Approved { by, post } => {
                (ApprovalAnswer::Approved, by.clone(), post.clone(), None)
            }
            Answer::Refused { by, post, reason } => (
                ApprovalAnswer::Refused,
                by.clone(),
                post.clone(),
                reason.clone(),
            ),
            Answer::Expired => (ApprovalAnswer::Expired, None, None, None),
        };
```

and in step 6, the `AuditEvent::Approval` field `post: None,` becomes `post,`.

In `admin.rs`, the two answers `bxctl` gives get `post: None,` after their `by: Some(BY.to_string()),`.

**3. `contains`.** In `approvals.rs`, `impl Table`, before `take`:

```rust
    /// Is approval `id` still pending? Only a hint: it may be taken the moment after.
    pub fn contains(&self, id: u64) -> bool {
        self.lock().contains_key(&id)
    }
```

## Steps

- [ ] **1. Copy.** `git switch m4b`, then
  `cp docs/plans/M4b/files/crates/brokerd/tests/ledger_post.rs docs/plans/M4b/files/crates/brokerd/tests/broker_pending.rs docs/plans/M4b/files/crates/brokerd/tests/broker_sequence.rs docs/plans/M4b/files/crates/brokerd/tests/ledger_answer.rs crates/brokerd/tests/`
- [ ] **2. See it fail.** `cargo test -p brokerd --test ledger_post`. Expected: it does not
  compile (`post` is not a field of `Answer`; `contains` does not exist).
- [ ] **3. Make the three changes.** Run `cargo fmt --all`.
- [ ] **4. See it pass.** `cargo test -p brokerd`. Expected: every suite passes; `ledger_post` 3
  passed. `wc -l crates/brokerd/src/ledger.rs` is under 490.
- [ ] **5. Run the gate.** `make gate`. Expected last line: `gate: ok`.
- [ ] **6. Log and commit.** `git add crates/brokerd docs/implementer-log.md Cargo.lock && git commit`

## Done when

- `cargo test -p brokerd` passes; `make gate` prints `gate: ok`.