PLAN.md

@@ -467,7 +467,7 @@ answers, and the trade is only acceptable because the lie is removed first.
 | M1 | **Cursors + wire polish** | getMore / killCursors / batchSize; server-side cursor state with idle timeout; sessions plumbing (lsid accepted) as drivers send it; hello advertisement updates; **`moreToCome` on requests** (see the bug below); command-monitoring assertions in the spec runner | crud spec suite green; e2e green |
 | M2 | **The `aggregate` command surface** | `$out` and `$merge` (7 of the 13 failures), and refusing every pipeline construct the engine does not implement instead of answering `0` (amendment A6). The other 6 failures are blocked on M2.5, M4 and M8 — see `docs/M2_DESIGN_REVIEW.md` §7 | `aggregate-*.json`: 0 fail among the 7 reachable cases |
 | M2.5 | **The aggregation engine** | expression evaluator, per-stage document iterator, the accumulators, `$unwind`; `$lookup`/`$facet` explicitly out of the first cut (amendment A6) | a purpose-built stage corpus, every expectation measured against mongod |
-| M3 | **Update operators + index types** | `distinct` (**done**); positional paths refused rather than destructive (**done**); `$`/`$[]`/`$[<ident>]` + `arrayFilters` implemented (**done**); then $setOnInsert, $addToSet, $mul, $min/$max, $pop, $pullAll, $currentDate, pipeline updates; partial + hashed indexes | `tests/spec/positional/` 0 fail (51 cases, recorded from mongod — **green**; the named gate could not see this work, see below); remaining crud coverage; e2e3/e2e4 green |
+| M3 | **Update operators + index types** | `distinct` (**done**); positional paths refused rather than destructive (**done**); `$`/`$[]`/`$[<ident>]` + `arrayFilters` (**done**); $setOnInsert, $addToSet, $mul, $min/$max, $pop, $pullAll, $currentDate + `$push`'s modifiers (**done**); then pipeline updates; partial + hashed indexes | `tests/spec/positional/` 0 fail (51 cases) and `tests/spec/operators/` 0 fail (102 cases), both recorded from mongod — **green**; the named gate could not see either, see below; remaining crud coverage; e2e3/e2e4 green |
 | M4 | **Sessions + transactions** | logical sessions, snapshot isolation on the mmap engine, write concern at commit | sessions + transactions spec suites green |
 | M5 | **Change streams** | change feed + resume tokens (likely log-seq based), getMore integration | change-streams spec suite green |
 | M6 | **Admin/ops commands** | dbStats, collStats, serverStatus, ping, buildInfo, listDatabases filters, dropDatabase durability (log it) | mongosh UX smoke; e2e green |
@@ -1123,6 +1123,28 @@ has to be its own commit with its own re-recorded scorecard.
     agrees. Worth one commit, and it needs its own measurements first: the
     padding case (`y.3.b` past the end) is a *legal* creation on mongod, so
     the fix is not "refuse a non-document element".
+- **M3's second corpus is `tests/spec/operators/`.** The eight operators PLAN
+  §3 names all answered `bad update` with code 2, one message for every
+  question — and `$push`'s `$slice`, `$position` and `$sort` were parsed,
+  accepted and *dropped*. `{$each: [3, 4], $slice: -3}` appended both values,
+  sliced nothing and answered ok: 1 with modifiedCount: 1, which is the same
+  class of wrong answer the positional operators were. 102 cases, recorded red
+  at 18/84 and driven green.
+
+  It found one thing that was nobody's operator: **an upsert never reported the
+  `_id` it generated**. `Engine.insert` writes a generated `_id` into the bytes
+  and leaves the caller's tree without it, so `upsertedId` came back null and
+  `findOneAndUpdate` with `returnDocument: after` returned a document with no
+  `_id` — the only name the client has for a document it has never seen. Fixed
+  in `build_upsert_doc`; the pinned crud corpus never noticed because its
+  upsert cases match `upsertedId` loosely.
+
+  Left open, measured and deliberate: `$bit` is not implemented (mongod has it,
+  no driver in `tests/` sends it, and it is not in the M3 row); `$sort` inside
+  `$push` accepts only a one-field key document, where mongod allows several;
+  and the conflict check stops after 64 distinct paths in one update rather
+  than refusing a legal wide update.
+
 - **M3 update operators** — open. `distinct` landed first because it was a
   whole missing command with no dependencies, and measuring it turned up three
   things worth keeping, none of which are `distinct`'s to fix:

src/commands.zig

@@ -66,6 +66,10 @@ pub const ErrorCode = enum(i32) {
     duplicate_key = 11000,
     namespace_exists = 48,
     failed_to_parse = 9,
+    /// `ConflictingUpdateOperators`, measured on mongod 8.3.7: two paths in
+    /// one update where either is a prefix of the other, so which of them
+    /// decides the result would depend on the order the operators ran in.
+    conflicting_update_operators = 40,
     internal_error = 1,
     /// "Unrecognized pipeline stage name". A `Location` code, so mongod names it
     /// `Location40324` rather than after any symbol.
@@ -1977,6 +1981,7 @@ fn cmd_update(ctx: *Context, msg: *wire.Message, reply: *wire.Reply) !void {
                 "update.updates.arrayFilters",
             ) orelse return,
             .query = q,
+            .now_ms = std.Io.Timestamp.now(ctx.io, .real).toMilliseconds(),
             .diag = &diag,
         };
         // Before the scan, not after: an update naming an identifier nothing
@@ -1991,7 +1996,7 @@ fn cmd_update(ctx: *Context, msg: *wire.Message, reply: *wire.Reply) !void {
 
         if (matched.items.len == 0) {
             if (upsert) {
-                const new_doc = build_upsert_doc(reply, q, u_doc, opts) catch |err|
+                const new_doc = build_upsert_doc(reply, ctx, q, u_doc, opts) catch |err|
                     return update_refusal(reply, err, diag);
                 ctx.engine.insert(db_name, coll_name, new_doc, ctx.oid_gen) catch |err| switch (err) {
                     error.DuplicateKey, error.DuplicateKeyIndex => return duplicate_key_error(ctx, reply, db_name, coll_name, new_doc),
@@ -2102,6 +2107,7 @@ fn cmd_find_and_modify(ctx: *Context, msg: *wire.Message, reply: *wire.Reply) !v
             "findAndModify.arrayFilters",
         ) orelse return,
         .query = q,
+        .now_ms = std.Io.Timestamp.now(ctx.io, .real).toMilliseconds(),
         .diag = &diag,
     };
     if (doc_arg(msg.body.get("update"))) |u| {
@@ -2132,7 +2138,7 @@ fn cmd_find_and_modify(ctx: *Context, msg: *wire.Message, reply: *wire.Reply) !v
 
     if (target == null and do_update and upsert) {
         const u_doc = doc_arg(msg.body.get("update")) orelse return bad_value(reply, "update must be a document");
-        const new_doc = build_upsert_doc(reply, q, u_doc, opts) catch |err|
+        const new_doc = build_upsert_doc(reply, ctx, q, u_doc, opts) catch |err|
             return update_refusal(reply, err, diag);
         ctx.engine.insert(db_name, coll_name, new_doc, ctx.oid_gen) catch |err| switch (err) {
             error.DuplicateKey, error.DuplicateKeyIndex => return duplicate_key_error(ctx, reply, db_name, coll_name, new_doc),
@@ -4253,6 +4259,97 @@ fn update_refusal(reply: *wire.Reply, err: anyerror, diag: update.Diagnostic) !v
                 "name, found '{s}' and '{s}'",
             .{ diag.segment, diag.other },
         )),
+        error.NotNumericField => return reply.put_error(
+            @intFromEnum(ErrorCode.type_mismatch),
+            "TypeMismatch",
+            try std.fmt.allocPrint(
+                arena,
+                "Cannot apply {s} to a value of non-numeric type. The field '{s}' is of " ++
+                    "non-numeric type {s}",
+                .{ diag.segment, diag.path, diag.other },
+            ),
+        ),
+        error.NotNumericOperand => return reply.put_error(
+            @intFromEnum(ErrorCode.type_mismatch),
+            "TypeMismatch",
+            try std.fmt.allocPrint(
+                arena,
+                "Cannot {s} with non-numeric argument at field '{s}'",
+                .{ if (std.mem.eql(u8, diag.segment, "$inc")) "increment" else "multiply", diag.path },
+            ),
+        ),
+        error.NotAnArrayField => return bad_value(reply, try std.fmt.allocPrint(
+            arena,
+            "Cannot apply {s} to non-array field. Field named '{s}' has non-array type",
+            .{ diag.segment, diag.path },
+        )),
+        error.NotAnArrayPathElement => return reply.put_error(
+            @intFromEnum(ErrorCode.type_mismatch),
+            "TypeMismatch",
+            try std.fmt.allocPrint(
+                arena,
+                "Path '{s}' contains an element of non-array type",
+                .{diag.path},
+            ),
+        ),
+        // mongod has two sentences here -- "$pop expects 1 or -1, found: 2"
+        // and "Expected a number in: t: \"x\"" -- both code 9, and both about
+        // an argument that is not one of the two values `$pop` takes. One
+        // sentence covering both says the same thing without rendering the
+        // operand, which no formatter here does.
+        error.BadPopArgument => return failed_to_parse(reply, try std.fmt.allocPrint(
+            arena,
+            "$pop expects 1 or -1, at field '{s}'",
+            .{diag.path},
+        )),
+        error.PullAllNeedsArray => return bad_value(reply, try std.fmt.allocPrint(
+            arena,
+            "$pullAll requires an array argument but was given a {s}",
+            .{diag.other},
+        )),
+        // `$push` and `$addToSet` disagree about the code for the identical
+        // mistake: 2 and 14. Measured on both, and not derivable from either.
+        error.BadEach => if (std.mem.eql(u8, diag.segment, "$addToSet")) return reply.put_error(
+            @intFromEnum(ErrorCode.type_mismatch),
+            "TypeMismatch",
+            "The argument to $each in $addToSet must be an array",
+        ) else return bad_value(reply, "The argument to $each in $push must be an array"),
+        error.BadPushModifier => return bad_value(reply, try std.fmt.allocPrint(
+            arena,
+            "Unrecognized or invalid $push modifier '{s}' at field '{s}'",
+            .{ diag.segment, diag.path },
+        )),
+        error.BadCurrentDateType => return bad_value(
+            reply,
+            "The '$type' string field is required to be 'date' or 'timestamp': " ++
+                "{$currentDate: {field : {$type: 'date'}}}",
+        ),
+        error.BadCurrentDateOperand => return bad_value(reply, try std.fmt.allocPrint(
+            arena,
+            "{s} is not valid type for $currentDate. Please use a boolean ('true') or a " ++
+                "$type expression ({{$type: 'timestamp/date'}}).",
+            .{diag.other},
+        )),
+        error.UnknownModifier => return failed_to_parse(reply, try std.fmt.allocPrint(
+            arena,
+            "Unknown modifier: {s}. Expected a valid update modifier or pipeline-style " ++
+                "update specified as an array",
+            .{diag.segment},
+        )),
+        error.ModifierNeedsFields => return failed_to_parse(reply, try std.fmt.allocPrint(
+            arena,
+            "Modifiers operate on fields but we found type {s} instead",
+            .{diag.segment},
+        )),
+        error.ConflictingUpdate => return reply.put_error(
+            @intFromEnum(ErrorCode.conflicting_update_operators),
+            "ConflictingUpdateOperators",
+            try std.fmt.allocPrint(
+                arena,
+                "Updating the path '{s}' would create a conflict at '{s}'",
+                .{ diag.path, diag.segment },
+            ),
+        ),
         error.PathNotViable => return reply.put_error(
             @intFromEnum(ErrorCode.path_not_viable),
             "PathNotViable",
@@ -4331,8 +4428,17 @@ fn wrong_type_dynamic(
 
 /// Build the document for an upsert: equality fields from the filter, then
 /// the update operators applied. Owned by the reply arena.
+///
+/// The `_id` is settled *here* rather than in the storage engine. `insert`
+/// generates one into the bytes it writes and leaves the caller's tree without
+/// it, so `updateOne(..., {upsert: true}).upsertedId` came back null and
+/// `findOneAndUpdate` with `returnDocument: after` returned a document missing
+/// its `_id`. Both are what the client is told about a document it has never
+/// seen, and both were wrong. Found by `tests/spec/operators/`, which is the
+/// first corpus here to upsert into an empty collection and then look.
 fn build_upsert_doc(
     reply: *wire.Reply,
+    ctx: *Context,
     q: []const bson.Pair,
     u_doc: []const bson.Pair,
     opts: update.Options,
@@ -4350,7 +4456,21 @@ fn build_upsert_doc(
     const owned = try arena.create(bson.Document);
     owned.* = bson.Document{ .arena = std.heap.ArenaAllocator.init(arena), .pairs = try pairs.toOwnedSlice(arena) };
     // Apply update operators to build the final doc; _id handled by insert.
-    try update.apply(owned, &.{ .arena = undefined, .pairs = u_doc }, opts);
+    // `inserting` is what `$setOnInsert` asks about, and this is the only
+    // caller that answers yes.
+    var insert_opts = opts;
+    insert_opts.inserting = true;
+    try update.apply(owned, &.{ .arena = undefined, .pairs = u_doc }, insert_opts);
+    // After the operators, because `$setOnInsert` may supply the `_id` itself
+    // and a generated one would then be the wrong answer. At the front,
+    // because that is where MongoDB stores it and where the `_id_` index
+    // descends on it.
+    if (owned.get("_id") == null) {
+        const with_id = try arena.alloc(bson.Pair, owned.pairs.len + 1);
+        with_id[0] = .{ .key = "_id", .value = .{ .object_id = ctx.oid_gen.new(ctx.io) } };
+        @memcpy(with_id[1..], owned.pairs);
+        owned.pairs = with_id;
+    }
     return owned;
 }
 
@@ -6981,3 +7101,57 @@ test "a rebuild kills an offsets cursor and spares a streaming one" {
     try testing.expectEqual(@as(i64, 0), id);
     try testing.expectEqual(@as(u32, 60), seen);
 }
+
+test "an upsert reports the _id it generated" {
+    // The client has never seen this document, so the `_id` in the reply is
+    // the only way it can name it again. `Engine.insert` generates one into
+    // the bytes it writes and leaves the caller's tree without it, so both
+    // `upserted` here and `findAndModify`'s returned document used to come
+    // back without an `_id` at all -- `upsertedId: null` on the driver.
+    //
+    // Mutation check: delete the `_id` block in `build_upsert_doc` and both
+    // halves go red.
+    var threaded: std.Io.Threaded = .init_single_threaded;
+    defer threaded.deinit();
+    const io = threaded.io();
+    var tdb = try TestDb.init(io);
+    defer tdb.deinit();
+    var ctx = tdb.ctx(io);
+
+    const updates = [_]bson.Value{.{ .doc = &.{
+        .{ .key = "q", .value = .{ .doc = &.{.{ .key = "k", .value = .{ .int32 = 1 } }} } },
+        .{ .key = "u", .value = .{ .doc = &.{
+            .{ .key = "$set", .value = .{ .doc = &.{.{ .key = "a", .value = .{ .int32 = 1 } }} } },
+        } } },
+        .{ .key = "upsert", .value = .{ .bool = true } },
+    } }};
+    var reply = wire.Reply.init(testing.allocator);
+    defer reply.deinit();
+    var msg = try parse_fake_msg("update", .{ .string = "up" }, &.{
+        .{ .key = "updates", .value = .{ .array = &updates } },
+    });
+    defer msg.deinit();
+    try dispatch(&ctx, &msg, &reply);
+    const upserted = bson.get_pair(reply.pairs.items, "upserted").?.array;
+    try testing.expectEqual(@as(usize, 1), upserted.len);
+    try testing.expect(bson.get_pair(upserted[0].doc, "_id").? == .object_id);
+
+    // And an `_id` the update supplied itself is the one that is used, rather
+    // than being generated over.
+    const with_id = [_]bson.Value{.{ .doc = &.{
+        .{ .key = "q", .value = .{ .doc = &.{.{ .key = "k", .value = .{ .int32 = 2 } }} } },
+        .{ .key = "u", .value = .{ .doc = &.{
+            .{ .key = "$setOnInsert", .value = .{ .doc = &.{.{ .key = "_id", .value = .{ .int32 = 9 } }} } },
+        } } },
+        .{ .key = "upsert", .value = .{ .bool = true } },
+    } }};
+    var reply2 = wire.Reply.init(testing.allocator);
+    defer reply2.deinit();
+    var msg2 = try parse_fake_msg("update", .{ .string = "up" }, &.{
+        .{ .key = "updates", .value = .{ .array = &with_id } },
+    });
+    defer msg2.deinit();
+    try dispatch(&ctx, &msg2, &reply2);
+    const upserted2 = bson.get_pair(reply2.pairs.items, "upserted").?.array;
+    try testing.expectEqual(@as(i32, 9), bson.get_pair(upserted2[0].doc, "_id").?.int32);
+}

tests/spec/operators/README.md

@@ -0,0 +1,109 @@
+# The update-operator corpus
+
+PLAN §3 lists eight update operators for M3 — `$setOnInsert`, `$addToSet`,
+`$mul`, `$min`, `$max`, `$pop`, `$pullAll`, `$currentDate` — and the pinned
+crud corpus says almost nothing about any of them. A probe running the
+identical update against mongod 8.3.7 and this server found:
+
+- all eight answering `bad update`, code 2, one message for every question;
+- `$push`'s `$slice`, `$position` and `$sort` **silently ignored**.
+  `{$each: [3, 4], $slice: -3}` appended both values, sliced nothing, and
+  answered `ok: 1` with `modifiedCount: 1`.
+
+The second is the reason this directory exists rather than a list of TODOs.
+A missing operator is an error the client can see; a modifier that is parsed,
+accepted and then dropped is the same class of wrong answer the positional
+operators were — the client asked for one thing and was told it got it.
+
+## The one rule
+
+**Inputs are authored here; expectations are measured against a real mongod.**
+
+```
+tests/spec/operators/
+  sources/*.json      documents + operations, authored
+  record.js           runs them against mongod, writes the expectations
+  *.json              generated, unified format, do not hand-edit
+```
+
+```sh
+mongod --port 27099 --dbpath <dir>
+node tests/spec/operators/record.js --mongod-port 27099
+node tests/spec/run.js --suite-dir tests/spec/operators
+```
+
+Same discipline as `tests/spec/positional/` and `tests/spec/aggregate/`, and
+for the same reason: a corpus written end to end here can encode our own bugs
+as expectations and then agree with us forever.
+
+## What cannot be recorded as a value
+
+Two things in this corpus are not predictable, and both are replaced by a
+`$$type` assertion rather than left out:
+
+- a `$currentDate` field is whatever the clock said. The case names it in
+  `volatile`, per case, so a corpus that one day wants to pin a real stored
+  date still can.
+- an upsert that inserts gets a generated ObjectId. That one is automatic:
+  no source file authors an ObjectId, so the rule is unambiguous.
+
+Everything else about the document — which fields exist, in what order,
+holding what — is still compared exactly. A case that dropped a field still
+fails.
+
+Files are written with canonical extended JSON (`relaxed: false`), which the
+runner already parses that way. It is verbose and it is exact: `$mul`
+overflowing an int32 produces an int64, and a corpus that wrote `4000000000`
+as a bare number would not have said so.
+
+## Where it stands
+
+Recorded against mongod 8.3.7. Green:
+
+```
+array-ops.json         26 pass   0 fail   0 skip
+current-date.json      11 pass   0 fail   0 skip
+modifiers.json         14 pass   0 fail   0 skip
+numeric.json           21 pass   0 fail   0 skip
+push-modifiers.json    21 pass   0 fail   0 skip
+set-on-insert.json      9 pass   0 fail   0 skip
+```
+
+It was recorded red — 18 pass / 84 fail against a server with none of these
+operators — and driven green by seven commits. The 18 that passed then were
+the shapes this server already answered mongod's way, mostly refusals that
+happened to agree.
+
+It also found a bug nothing else here had: an upsert never reported the `_id`
+it generated, so `updateOne(..., {upsert: true}).upsertedId` was null and
+`findOneAndUpdate` with `returnDocument: after` returned a document with no
+`_id`. This is the first corpus here that upserts into an empty collection and
+then looks at what came back.
+
+## What recording it settled
+
+None of this is guessable, and several rows contradict the obvious reading:
+
+| | mongod |
+|---|---|
+| `$mul` of a missing field | writes **0**, not the operand |
+| `$mul` of a non-numeric field, or by one | TypeMismatch (14) |
+| `$min`/`$max` across types | compares in BSON canonical order, so `$min: {s: 5}` on `s: "b"` writes 5 |
+| `$min`/`$max` of a missing field | always writes |
+| two operators writing one field | **ConflictingUpdateOperators (40)** — `$min`+`$max`, `$set`+`$inc`, `$setOnInsert`+`$set` |
+| `$addToSet` of a document | compares whole, **field order included**: `{a:1,b:2}` and `{b:2,a:1}` are two values |
+| `$addToSet` of `2` and `2.0` | one value |
+| `$pop` of an empty or missing field | no-op, not an error |
+| `$pop` with an argument that is not ±1 | FailedToParse (9); on a non-array field, TypeMismatch (14) |
+| `$pullAll` with a non-array argument | BadValue (2) |
+| `$push` modifiers without `$each` | **not modifiers at all** — `{$slice: 1}` is pushed as a value |
+| `$push` modifier order | insert at `$position`, then `$sort` the whole array, then `$slice` |
+| `$position` negative | counted from the end |
+| `$currentDate` with `false` | still writes a date; the boolean's value is ignored |
+| `$currentDate` with anything but a bool or `{$type: date\|timestamp}` | BadValue (2) |
+| `$setOnInsert` writing `_id` on an insert | **allowed**, unlike `$set` |
+| an unknown modifier | FailedToParse (9), not BadValue |
+
+One case was authored and then removed: `{b: 1, $set: {c: 1}}` is rejected by
+the driver before it reaches a server, so there is no server answer to record
+and the case would have asserted nothing.

tests/spec/operators/record.js

@@ -0,0 +1,222 @@
+// Record an update-operator corpus by asking a real mongod what the answer is.
+//
+// Eight operators PLAN §3 lists for M3 -- `$setOnInsert`, `$addToSet`, `$mul`,
+// `$min`, `$max`, `$pop`, `$pullAll`, `$currentDate` -- plus `$push`'s
+// `$slice`/`$position`/`$sort` modifiers. The pinned crud corpus contains
+// almost nothing about any of them, and a probe against both servers found
+// every one of the eight answering `bad update` here, and the three `$push`
+// modifiers *silently ignored*: `{$each: [3, 4], $slice: -3}` appended without
+// slicing and answered ok: 1. Same discipline as `tests/spec/positional/` and
+// `tests/spec/aggregate/`: inputs are authored in `sources/`, expectations are
+// measured here.
+//
+//   node tests/spec/operators/record.js --mongod-port 27099
+//
+// Options:
+//   --mongod-port <n>  a running mongod to measure against (default 27099)
+//   --only <name>      record just one source file
+const fs = require('fs');
+const path = require('path');
+// The same pinned driver `run.js` uses, resolved the same way.
+const DRIVER = path.join(__dirname, '..', '..', 'e2e', 'node_modules', 'mongodb');
+const { MongoClient } = require(DRIVER);
+const { EJSON, ObjectId, Timestamp } = require(path.join(DRIVER, 'lib', 'bson.js'));
+
+const argv = process.argv.slice(2);
+function opt(name, dflt) {
+    const i = argv.indexOf('--' + name);
+    if (i < 0) return dflt;
+    const v = argv[i + 1];
+    return v === undefined || v.startsWith('--') ? true : v;
+}
+
+const PORT = parseInt(opt('mongod-port', '27099'), 10);
+const ONLY = opt('only', null);
+const SRC_DIR = path.join(__dirname, 'sources');
+const DB_NAME = 'operator-corpus';
+const COLL = 'coll';
+
+// Every construct here predates 4.0, so nothing depends on a server newer than
+// the 4.4 this one reports.
+const SCHEMA_VERSION = '1.4';
+
+const UPDATE_KEYS = ['matchedCount', 'modifiedCount', 'upsertedCount'];
+
+/// Values nobody can predict, replaced by an assertion about their type.
+///
+/// Two kinds, and both are the corpus staying honest rather than the corpus
+/// looking away: a `$currentDate` field is whatever the clock said, and an
+/// upsert that inserts gets a generated ObjectId. Everything else about the
+/// document -- which fields exist, in what order, holding what -- is still
+/// compared exactly, so a case that lost a field still fails.
+///
+/// The ObjectId rule is automatic because it is unambiguous: no source file
+/// authors one. A date is not: `volatile` names those per case, so a corpus
+/// that one day wants to pin a real stored date still can.
+function maskGenerated(value) {
+    if (value instanceof ObjectId) return { $$type: 'objectId' };
+    if (Array.isArray(value)) return value.map(maskGenerated);
+    if (value && typeof value === 'object' && value.constructor === Object) {
+        const out = {};
+        for (const [k, v] of Object.entries(value)) out[k] = maskGenerated(v);
+        return out;
+    }
+    return value;
+}
+
+function maskVolatile(docs, paths) {
+    for (const p of paths) {
+        for (const doc of docs) {
+            const segs = p.split('.');
+            let cur = doc;
+            for (const s of segs.slice(0, -1)) cur = cur === undefined ? undefined : cur[s];
+            const last = segs[segs.length - 1];
+            if (cur === undefined || !(last in cur)) {
+                throw new Error(`volatile path '${p}' is not in the recorded document ` +
+                    `${JSON.stringify(doc)} -- the case did not write what it said it would`);
+            }
+            const v = cur[last];
+            if (v instanceof Date) cur[last] = { $$type: 'date' };
+            else if (v instanceof Timestamp) cur[last] = { $$type: 'timestamp' };
+            else throw new Error(`volatile path '${p}' holds ${v}, which is neither a date nor a timestamp`);
+        }
+    }
+}
+
+async function main() {
+    if (!fs.existsSync(SRC_DIR)) {
+        console.error(`missing ${SRC_DIR}`);
+        process.exit(2);
+    }
+    const client = new MongoClient(`mongodb://127.0.0.1:${PORT}`, { serverSelectionTimeoutMS: 3000 });
+    try {
+        await client.connect();
+    } catch (e) {
+        console.error(`no mongod on :${PORT} -- start one first:\n` +
+            `  mongod --port ${PORT} --dbpath <dir>\n${e.message}`);
+        process.exit(2);
+    }
+    const build = await client.db('admin').command({ buildInfo: 1 });
+    console.log(`recording against mongod ${build.version} on :${PORT}`);
+
+    const sources = fs.readdirSync(SRC_DIR).filter((f) => f.endsWith('.json'))
+        .filter((f) => !ONLY || f === ONLY || f === ONLY + '.json')
+        .sort();
+    if (!sources.length) {
+        console.error('no source files');
+        process.exit(2);
+    }
+
+    for (const file of sources) {
+        const src = JSON.parse(fs.readFileSync(path.join(SRC_DIR, file), 'utf8'));
+        const name = path.basename(file, '.json');
+        const out = await record(client, name, src);
+        const text = EJSON.stringify(out, { relaxed: false, indent: 2 });
+        fs.writeFileSync(path.join(__dirname, `${name}.json`), text + '\n');
+        const errs = out.tests.filter((t) => t.operations[t.operations.length - 1].expectError).length;
+        console.log(`  ${name}: ${out.tests.length} cases, ${errs} of them errors`);
+    }
+    await client.close();
+    console.log('RECORDED');
+}
+
+async function record(client, name, src) {
+    const coll = client.db(DB_NAME).collection(COLL);
+    const tests = [];
+
+    for (const c of src.cases) {
+        const documents = c.documents === undefined ? src.documents : c.documents;
+        await coll.drop().catch(() => {});
+        if (documents.length) await coll.insertMany(structuredClone(documents));
+
+        // A case that brings its own documents reseeds through *operations*:
+        // the unified format's `initialData` is per file, and the runner seeds
+        // it once per test.
+        const setup = [];
+        if (c.documents !== undefined) {
+            setup.push({ object: 'collection0', name: 'deleteMany', arguments: { filter: {} } });
+            if (documents.length) {
+                setup.push({
+                    object: 'collection0',
+                    name: 'insertMany',
+                    arguments: { documents: structuredClone(documents) },
+                });
+            }
+        }
+        const op = {
+            object: 'collection0',
+            name: c.operation,
+            arguments: structuredClone(c.arguments),
+        };
+        try {
+            op.expectResult = maskGenerated(await invoke(coll, c.operation, structuredClone(c.arguments)));
+        } catch (e) {
+            // The code, not the message: message text is mongod's to change
+            // between releases, and several of these embed a rendering of the
+            // offending BSON that no formatter here produces.
+            delete op.expectResult;
+            op.expectError = { isError: true, errorCode: e.code };
+        }
+
+        // Recorded for every case including the refusals: a refusal that left
+        // the document half-written would look identical to a clean one in
+        // `expectError` alone.
+        const after = await coll.find({}, { sort: { _id: 1 } }).toArray();
+        if (c.volatile) maskVolatile(after, c.volatile);
+
+        tests.push({
+            description: c.description,
+            operations: [...setup, op],
+            outcome: [{
+                collectionName: COLL,
+                databaseName: DB_NAME,
+                documents: after.map(maskGenerated),
+            }],
+        });
+    }
+    await coll.drop().catch(() => {});
+
+    return {
+        description: name,
+        schemaVersion: SCHEMA_VERSION,
+        // Recorded, not authored. Regenerate with tests/spec/operators/record.js.
+        createEntities: [
+            { client: { id: 'client0' } },
+            { database: { id: 'database0', client: 'client0', databaseName: DB_NAME } },
+            { collection: { id: 'collection0', database: 'database0', collectionName: COLL } },
+        ],
+        initialData: [{ collectionName: COLL, databaseName: DB_NAME, documents: src.documents }],
+        tests,
+    };
+}
+
+async function invoke(coll, name, args) {
+    const { filter, update, replacement, ...rest } = args;
+    switch (name) {
+        case 'updateOne':
+            return pick(await coll.updateOne(filter, update, rest), UPDATE_KEYS);
+        case 'updateMany':
+            return pick(await coll.updateMany(filter, update, rest), UPDATE_KEYS);
+        case 'replaceOne':
+            return pick(await coll.replaceOne(filter, replacement, rest), UPDATE_KEYS);
+        case 'findOneAndUpdate': {
+            const r = await coll.findOneAndUpdate(filter, update, rest);
+            // Driver 5+ returns the document itself; 4.x wrapped it in
+            // `{value}`. run.js tolerates both the same way.
+            return r && typeof r === 'object' && 'value' in r && 'ok' in r ? r.value : r;
+        }
+        default:
+            throw new Error(`record.js does not know the operation '${name}'`);
+    }
+}
+
+function pick(result, keys) {
+    const o = {};
+    for (const k of keys) if (result[k] !== undefined) o[k] = result[k];
+    return o;
+}
+
+main().catch((e) => {
+    console.error('RECORD_FAIL', e);
+    process.exit(1);
+});

tests/spec/operators/sources/array-ops.json

@@ -0,0 +1,153 @@
+{
+  "_comment": [
+    "Inputs only. Expectations are measured -- see record.js.",
+    "`$addToSet`, `$pop` and `$pullAll`: the three array operators that are",
+    "neither `$push` nor `$pull`. Each has a shape that decides whether it",
+    "wrote at all -- a set that already held the value, a pop of an empty",
+    "array, a pullAll matching nothing -- and `modifiedCount` is the only",
+    "place that shows, which is why every case records an outcome too."
+  ],
+  "documents": [{ "_id": 1, "t": [1, 2, 3] }],
+  "cases": [
+    {
+      "description": "$addToSet appends a value the array does not hold",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 4 } } }
+    },
+    {
+      "description": "$addToSet on a value already there writes nothing",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 2 } } }
+    },
+    {
+      "description": "$addToSet on a missing field creates the array",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "gone": 1 } } }
+    },
+    {
+      "description": "$addToSet $each adds only what is missing",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "$each": [2, 4, 5] } } } }
+    },
+    {
+      "description": "$addToSet $each with duplicates inside it",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "$each": [7, 7] } } } }
+    },
+    {
+      "description": "$addToSet compares documents whole",
+      "documents": [{ "_id": 1, "t": [{ "a": 1 }] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "a": 1 } } } }
+    },
+    {
+      "description": "$addToSet distinguishes documents by field order",
+      "documents": [{ "_id": 1, "t": [{ "a": 1, "b": 2 }] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": { "b": 2, "a": 1 } } } }
+    },
+    {
+      "description": "$addToSet treats an int and an equal double as one value",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 2.0 } } }
+    },
+    {
+      "description": "$addToSet on a non-array field",
+      "documents": [{ "_id": 1, "t": 5 }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "t": 1 } } }
+    },
+    {
+      "description": "$pop removes the last element",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
+    },
+    {
+      "description": "$pop with -1 removes the first",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": -1 } } }
+    },
+    {
+      "description": "$pop of an empty array writes nothing",
+      "documents": [{ "_id": 1, "t": [] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
+    },
+    {
+      "description": "$pop of a missing field writes nothing",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "gone": 1 } } }
+    },
+    {
+      "description": "$pop of a one-element array leaves an empty one",
+      "documents": [{ "_id": 1, "t": [9] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
+    },
+    {
+      "description": "$pop with an argument that is neither 1 nor -1",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": 2 } } }
+    },
+    {
+      "description": "$pop with 1.0, which is 1",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": 1.0 } } }
+    },
+    {
+      "description": "$pop of a non-array field",
+      "documents": [{ "_id": 1, "t": 5 }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "t": 1 } } }
+    },
+    {
+      "description": "$pullAll removes every copy of every listed value",
+      "documents": [{ "_id": 1, "t": [1, 2, 3, 2] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [2] } } }
+    },
+    {
+      "description": "$pullAll with several values",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [1, 3] } } }
+    },
+    {
+      "description": "$pullAll matching nothing writes nothing",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [9] } } }
+    },
+    {
+      "description": "$pullAll compares documents whole, not by predicate",
+      "documents": [{ "_id": 1, "t": [{ "a": 1 }, { "a": 2 }] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [{ "a": 1 }] } } }
+    },
+    {
+      "description": "$pullAll on a missing field writes nothing",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "gone": [1] } } }
+    },
+    {
+      "description": "$pullAll with an argument that is not an array",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "t": 1 } } }
+    },
+    {
+      "description": "$pullAll emptying the array",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pullAll": { "t": [1, 2, 3] } } }
+    },
+    {
+      "description": "$addToSet through a positional segment",
+      "documents": [{ "_id": 1, "y": [{ "t": [1] }, { "t": [2] }] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$addToSet": { "y.$[].t": 1 } } }
+    },
+    {
+      "description": "$pop down a dotted path",
+      "documents": [{ "_id": 1, "n": { "t": [1, 2] } }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pop": { "n.t": -1 } } }
+    }
+  ]
+}

tests/spec/operators/sources/current-date.json

@@ -0,0 +1,81 @@
+{
+  "_comment": [
+    "Inputs only. Expectations are measured -- see record.js.",
+    "`$currentDate`, the one update operator whose result cannot be recorded",
+    "as a value: it is whatever the clock said. `volatile` names the fields",
+    "whose recorded value is replaced by a `$$type` assertion, so the case",
+    "still pins the type, the position and every other field of the document",
+    "-- everything except the number nobody can predict."
+  ],
+  "documents": [{ "_id": 1, "a": 1 }],
+  "cases": [
+    {
+      "description": "$currentDate with true writes a date",
+      "volatile": ["d"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": true } } }
+    },
+    {
+      "description": "$currentDate with an explicit date type",
+      "volatile": ["d"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": { "$type": "date" } } } }
+    },
+    {
+      "description": "$currentDate with the timestamp type",
+      "volatile": ["d"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": { "$type": "timestamp" } } } }
+    },
+    {
+      "description": "$currentDate overwrites a field that is already there",
+      "volatile": ["a"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "a": true } } }
+    },
+    {
+      "description": "$currentDate down a dotted path",
+      "volatile": ["n.d"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "n.d": true } } }
+    },
+    {
+      "description": "$currentDate beside another operator",
+      "volatile": ["d"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": true }, "$inc": { "a": 1 } } }
+    },
+    {
+      "description": "$currentDate with false, which is still a date",
+      "volatile": ["d"],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": false } } }
+    },
+    {
+      "description": "$currentDate with an unknown type name",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": { "$type": "nope" } } } }
+    },
+    {
+      "description": "$currentDate with a document that is not $type",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": { "a": 1 } } } }
+    },
+    {
+      "description": "$currentDate with a number",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$currentDate": { "d": 1 } } }
+    },
+    {
+      "description": "$currentDate on an upsert that inserts",
+      "documents": [],
+      "volatile": ["d"],
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$currentDate": { "d": true } },
+        "upsert": true
+      }
+    }
+  ]
+}

tests/spec/operators/sources/modifiers.json

@@ -0,0 +1,88 @@
+{
+  "_comment": [
+    "Inputs only. Expectations are measured -- see record.js.",
+    "The operator table itself, rather than any one operator: what an update",
+    "document may be, and what happens to a name that is not in the table.",
+    "This server answers `bad update` with code 2 to every one of these, which",
+    "is one message covering several different questions.",
+    "A `{b: 1, $set: {...}}` case was authored and then removed: the driver",
+    "rejects it before it reaches a server, so there is no server answer to",
+    "record and a case with no `errorCode` would assert nothing."
+  ],
+  "documents": [{ "_id": 1, "a": 1, "t": [1, 2] }],
+  "cases": [
+    {
+      "description": "an unknown modifier",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$bogus": { "a": 1 } } }
+    },
+    {
+      "description": "an unknown modifier beside a known one",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$set": { "b": 1 }, "$bogus": { "a": 1 } } }
+    },
+    {
+      "description": "a known modifier whose argument is not a document",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$set": 1 } }
+    },
+    {
+      "description": "an empty argument to a known modifier",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$set": {} } }
+    },
+    {
+      "description": "a data field after an operator",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$set": { "c": 1 }, "b": 1 } }
+    },
+    {
+      "description": "two operators writing the same field",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$set": { "a": 2 }, "$inc": { "a": 1 } } }
+    },
+    {
+      "description": "$inc on a non-numeric field",
+      "documents": [{ "_id": 1, "a": "x" }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$inc": { "a": 1 } } }
+    },
+    {
+      "description": "$inc by a non-numeric operand",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$inc": { "a": "x" } } }
+    },
+    {
+      "description": "$push onto a non-array field",
+      "documents": [{ "_id": 1, "t": 5 }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": 1 } } }
+    },
+    {
+      "description": "$pull on a non-array field",
+      "documents": [{ "_id": 1, "t": 5 }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$pull": { "t": 1 } } }
+    },
+    {
+      "description": "$unset of a field that is not there",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$unset": { "gone": "" } } }
+    },
+    {
+      "description": "$rename onto a field that already exists",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$rename": { "a": "t" } } }
+    },
+    {
+      "description": "$rename of a field that is not there",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$rename": { "gone": "b" } } }
+    },
+    {
+      "description": "an update that writes nothing still reports a match",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$set": { "a": 1 } } }
+    }
+  ]
+}

tests/spec/operators/sources/numeric.json

@@ -0,0 +1,122 @@
+{
+  "_comment": [
+    "Inputs only. Expectations are measured -- see record.js.",
+    "`$mul`, `$min` and `$max`. The two comparison operators are not numeric",
+    "at all -- they compare in BSON canonical order, which is why a string",
+    "field and a number operand have a defined answer -- and the cases here",
+    "are shaped to say which of the three rules each one follows."
+  ],
+  "documents": [{ "_id": 1, "a": 5, "s": "b", "d": 2.5 }],
+  "cases": [
+    {
+      "description": "$mul multiplies an int by an int",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "a": 2 } } }
+    },
+    {
+      "description": "$mul of a missing field",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "gone": 5 } } }
+    },
+    {
+      "description": "$mul mixes int and double",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "d": 2 } } }
+    },
+    {
+      "description": "$mul by zero",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "a": 0 } } }
+    },
+    {
+      "description": "$mul overflowing an int32",
+      "documents": [{ "_id": 1, "a": 2000000000 }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "a": 2 } } }
+    },
+    {
+      "description": "$mul of a non-numeric field",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "s": 2 } } }
+    },
+    {
+      "description": "$mul by a non-numeric operand",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "a": "x" } } }
+    },
+    {
+      "description": "$mul down a dotted path",
+      "documents": [{ "_id": 1, "n": { "a": 3 } }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "n.a": 4 } } }
+    },
+    {
+      "description": "$min writes when the operand is lower",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "a": 3 } } }
+    },
+    {
+      "description": "$min leaves the field when the operand is higher",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "a": 7 } } }
+    },
+    {
+      "description": "$min of a missing field always writes",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "gone": 7 } } }
+    },
+    {
+      "description": "$min against a field of another type",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "s": 5 } } }
+    },
+    {
+      "description": "$min compares an int and an equal double",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "a": 5.0 } } }
+    },
+    {
+      "description": "$max writes when the operand is higher",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$max": { "a": 7 } } }
+    },
+    {
+      "description": "$max leaves the field when the operand is lower",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$max": { "a": 3 } } }
+    },
+    {
+      "description": "$max of a missing field always writes",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$max": { "gone": 7 } } }
+    },
+    {
+      "description": "$max against a field of another type",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$max": { "s": 5 } } }
+    },
+    {
+      "description": "$max against a null field",
+      "documents": [{ "_id": 1, "a": null }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$max": { "a": 1 } } }
+    },
+    {
+      "description": "$min and $max on the same field in one update",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "a": 3 }, "$max": { "a": 9 } } }
+    },
+    {
+      "description": "$min through an array index",
+      "documents": [{ "_id": 1, "t": [5, 5] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$min": { "t.0": 1 } } }
+    },
+    {
+      "description": "$mul through a positional segment",
+      "documents": [{ "_id": 1, "t": [{ "a": 2 }, { "a": 3 }] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$mul": { "t.$[].a": 10 } } }
+    }
+  ]
+}

tests/spec/operators/sources/push-modifiers.json

@@ -0,0 +1,122 @@
+{
+  "_comment": [
+    "Inputs only. Expectations are measured -- see record.js.",
+    "`$push`'s modifiers: `$each`, `$slice`, `$position`, `$sort`. This server",
+    "already implements `$push` and `$each` and *silently ignores* the other",
+    "three -- `{$each: [3, 4], $slice: -3}` appended and did not slice, and",
+    "answered ok: 1. That is the same class of wrong answer the positional",
+    "operators were: the client asked for one thing and was told it got it."
+  ],
+  "documents": [{ "_id": 1, "t": [1, 2] }],
+  "cases": [
+    {
+      "description": "$slice keeps the last n",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3, 4], "$slice": -3 } } } }
+    },
+    {
+      "description": "$slice keeps the first n",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3, 4], "$slice": 3 } } } }
+    },
+    {
+      "description": "$slice of zero empties the array",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3], "$slice": 0 } } } }
+    },
+    {
+      "description": "$slice larger than the array keeps all of it",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3], "$slice": 10 } } } }
+    },
+    {
+      "description": "$slice with an empty $each truncates without adding",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [], "$slice": 1 } } } }
+    },
+    {
+      "description": "$position inserts at the front",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [9], "$position": 0 } } } }
+    },
+    {
+      "description": "$position inserts in the middle",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [9], "$position": 1 } } } }
+    },
+    {
+      "description": "$position past the end appends",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [9], "$position": 99 } } } }
+    },
+    {
+      "description": "$position counted from the end",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [9], "$position": -1 } } } }
+    },
+    {
+      "description": "$sort ascending over scalars",
+      "documents": [{ "_id": 1, "t": [3, 1] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [2], "$sort": 1 } } } }
+    },
+    {
+      "description": "$sort descending over scalars",
+      "documents": [{ "_id": 1, "t": [3, 1] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [2], "$sort": -1 } } } }
+    },
+    {
+      "description": "$sort on a field of the elements",
+      "documents": [{ "_id": 1, "t": [{ "a": 3 }, { "a": 1 }] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [{ "a": 2 }], "$sort": { "a": 1 } } } } }
+    },
+    {
+      "description": "$sort and $slice together",
+      "documents": [{ "_id": 1, "t": [3, 1] }],
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [2], "$sort": 1, "$slice": 2 } } } }
+    },
+    {
+      "description": "$position and $slice together",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [9], "$position": 0, "$slice": 2 } } } }
+    },
+    {
+      "description": "$slice without $each",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$slice": 1 } } } }
+    },
+    {
+      "description": "$each that is not an array",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": 3 } } } }
+    },
+    {
+      "description": "$slice that is not a number",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3], "$slice": "x" } } } }
+    },
+    {
+      "description": "$position that is not a number",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3], "$position": "x" } } } }
+    },
+    {
+      "description": "an unknown modifier beside $each",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "$each": [3], "$bogus": 1 } } } }
+    },
+    {
+      "description": "a document operand that is not modifiers at all is a value",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "t": { "a": 1 } } } }
+    },
+    {
+      "description": "$push $each onto a missing field",
+      "operation": "updateOne",
+      "arguments": { "filter": {}, "update": { "$push": { "gone": { "$each": [1, 2] } } } }
+    }
+  ]
+}

tests/spec/operators/sources/set-on-insert.json

@@ -0,0 +1,99 @@
+{
+  "_comment": [
+    "Inputs only. Expectations are measured -- see record.js.",
+    "`$setOnInsert`, the only update operator whose meaning depends on which",
+    "branch of an upsert ran. Every case here is therefore a pair: the same",
+    "update against a document that exists and against one that does not."
+  ],
+  "documents": [{ "_id": 1, "k": 1, "a": 100 }],
+  "cases": [
+    {
+      "description": "$setOnInsert writes when the upsert inserts",
+      "documents": [],
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "a": 1 }, "$set": { "b": 2 } },
+        "upsert": true
+      }
+    },
+    {
+      "description": "$setOnInsert is ignored when the upsert updates",
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "a": 1 }, "$set": { "b": 2 } },
+        "upsert": true
+      }
+    },
+    {
+      "description": "$setOnInsert alone on a plain update is a no-op",
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "a": 1 } }
+      }
+    },
+    {
+      "description": "$setOnInsert alone on an insert is the whole document",
+      "documents": [],
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 7 },
+        "update": { "$setOnInsert": { "a": 1 } },
+        "upsert": true
+      }
+    },
+    {
+      "description": "$setOnInsert writes a dotted path on insert",
+      "documents": [],
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "x.y": 5 } },
+        "upsert": true
+      }
+    },
+    {
+      "description": "$setOnInsert may not touch _id",
+      "documents": [],
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "_id": 9 } },
+        "upsert": true
+      }
+    },
+    {
+      "description": "$setOnInsert and $set naming the same field on an insert",
+      "documents": [],
+      "operation": "updateOne",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "a": 1 }, "$set": { "a": 2 } },
+        "upsert": true
+      }
+    },
+    {
+      "description": "findOneAndUpdate reports the document $setOnInsert built",
+      "documents": [],
+      "operation": "findOneAndUpdate",
+      "arguments": {
+        "filter": { "k": 3 },
+        "update": { "$setOnInsert": { "a": 1 } },
+        "upsert": true,
+        "returnDocument": "after"
+      }
+    },
+    {
+      "description": "updateMany with $setOnInsert on an upsert that inserts",
+      "documents": [],
+      "operation": "updateMany",
+      "arguments": {
+        "filter": { "k": 1 },
+        "update": { "$setOnInsert": { "a": 1 } },
+        "upsert": true
+      }
+    }
+  ]
+}

tests/spec/run.js

@@ -44,9 +44,9 @@ function opt(name, dflt) {
 }
 const VERBOSE = !!opt('verbose', false);
 // The corpus. Defaults to the pinned crud suite; `--suite-dir` points the same
-// runner at another one, which is how `tests/spec/aggregate/` and
-// `tests/spec/positional/` are run -- both exist because the pinned suite has
-// a hole where a whole feature should be. Sharing
+// runner at another one, which is how `tests/spec/aggregate/`,
+// `tests/spec/positional/` and `tests/spec/operators/` are run -- each exists
+// because the pinned suite has a hole where a whole feature should be. Sharing
 // the runner rather than writing a second one is the point: the entity model,
 // the matchers, the skip accounting and `expectEvents` all come for free, and a
 // second runner would drift from this one exactly where it mattered.