27 cases, recorded before a line of the evaluator is written, which is the
whole point of having built the recorder first: the expectations come from
mongod 8.3.7 rather than from what the implementation is about to do.
The corpus reads 1 pass / 26 fail, and the one pass is the unknown-operator
refusal M2 already answers correctly. Expressions are exercised through
`$group` because `_id` and the accumulator arguments are the only expression
positions that exist until `$addFields` and `$project`'s computed fields land;
testing them anywhere else would be testing a stage that is not there.
Ten things the recording settled that guessing would have got wrong:
$add over a missing field or null null -- not an error, and not 0
$add over a string error 7157723
$divide by zero error 4848401
$mod of -5 by 4 -1, the dividend's sign
$lt of a number and a string true, canonical type order
$and over -5 truthy
$not of a missing field true
$switch, no branch and no default error 40069
two operators in one expression error 15983, *not* $group's 40238
$subtract with one operand error 16020
The six error codes are in `ErrorCode` already, so the evaluator's refusals and
its runtime failures have somewhere measured to land. The evaluator itself is
the next commit and is not started.
191/191 unit tests, crud corpus unchanged at 201/90/196.
M2.5's gate, built before the milestone it gates -- the same order that put
`expectEvents` before the free list in M1 and Tier 0 before everything in M2.
`mongodb/specifications` has no aggregation suite, which is amendment A6's
central finding, so this milestone has to bring its own. The hazard in a corpus
we author is obvious and fatal: it can encode our own bugs as expectations and
then agree with us forever. So the split is enforced by the tooling.
`sources/*.json` holds documents and pipelines and nothing else; `record.js`
asks a real mongod 8.3.7 what each pipeline answers and writes the unified-
format file from the reply. Inputs authored, expectations measured -- the
discipline that corrected three assumptions in M1's session work and every
error code in M2, where the alternative would have shipped both times.
No second runner. `run.js --suite-dir` points the existing one somewhere else,
so the entity model, the matchers, the skip accounting and `expectEvents` come
for free; a second runner would drift from the first exactly where it mattered.
`--scorecard` is refused with `--suite-dir`, because `scorecard.txt` is the crud
corpus's record and the milestones are compared against it -- writing it from an
unrelated run would replace that record silently.
Errors record the code and not the message: message text is mongod's to change
between releases. Group pipelines end in a `$sort`, because group output order
is unspecified and a case depending on it would fail for the wrong reason on
either server.
The first source covers `$group`: nine accumulators including the edge cases
that decide an implementation -- `$avg` over a group whose values are not
numbers, `$min` of a field no document has, `$push` skipping a missing field,
`$first`/`$last` against input order, grouping on an array, a compound `_id`.
Where it starts, run against the M2 tip:
group-accumulators.json 9 pass 10 fail 0 skip
The nine include the four refusals M2 added, which answer with mongod's own
codes -- so the corpus already confirms that half. The ten are the milestone.
The crud corpus is unchanged at 201/90/196.
