feat(completion): complete mongo projection operators

apps/desktop/src/lib/mongo/mongoCompletion.ts

@@ -12,6 +12,7 @@ import {
   BULK_WRITE_OPERATIONS,
   KEY_MAP_VALUES,
   METHOD_OPTION_KEYS,
+  PROJECTION_OPERATORS,
   OPERATOR_SUB_KEYS,
   STAGE_OPTION_KEYS,
   TOP_LEVEL_QUERY_OPERATORS,
@@ -51,6 +52,7 @@ export type MongoCompletionMode =
   | "queryOperator"
   | "updateOperator"
   | "pushModifier"
+  | "projectionOperator"
   | "expression"
   | "accumulator"
   | "windowOperator"
@@ -504,6 +506,9 @@ export function buildMongoCompletionItemsFromContext(context: MongoCompletionCon
     case "pushModifier":
       items = specItems(PUSH_MODIFIERS, prefix, "array update modifier", 100);
       break;
+    case "projectionOperator":
+      items = specItems(PROJECTION_OPERATORS, prefix, "projection operator", 100);
+      break;
     case "expression":
       items = [...specItems(EXPRESSION_OPERATORS, prefix, "aggregation expression", 100), ...fieldRefItems(prefix, fields, 80)];
       break;
@@ -1031,14 +1036,43 @@ function classifyDocument(scan: MongoCallScan, rootIndex: number): MongoCompleti
  * Keys are field names; values are the small fixed set `keyMap` names.
  */
 function classifyKeyMap(scan: MongoCallScan, rootIndex: number, keyMap: string): MongoCursorClass {
+  if (keyMap === "projection") return classifyFindProjection(scan, rootIndex);
   const inner = innermost(scan);
   if (!inner || inner.kind !== "object" || innerDepth(scan, rootIndex) !== 0) return { mode: "none" };
   if (scan.inValue) return { mode: scan.inString ? "none" : "keyMapValue", keyMap };
   return { mode: "field" };
 }
 
-/** Option keys whose value is a field-to-value map, so the cursor completes field names there. */
-const FIELD_MAP_OPTION_KEYS = new Set(["sort", "projection"]);
+/**
+ * A find-style projection: `find({}, { ... })`, `findOne({}, { ... })`, or `{ projection: { ... } }`.
+ * At the root level, keys are field names and values are 1/0. One level in, keys are projection
+ * operators (`$slice`, `$elemMatch`, `$meta`).
+ */
+function classifyFindProjection(scan: MongoCallScan, rootIndex: number): MongoCursorClass {
+  const inner = innermost(scan);
+  const depth = innerDepth(scan, rootIndex);
+  if (!inner || depth < 0) return { mode: "none" };
+
+  const elemMatchIndex = findContainerIndex(scan, rootIndex, "$elemMatch");
+  if (elemMatchIndex >= 0) return classifyFilter(scan, elemMatchIndex);
+
+  if (depth === 0) {
+    if (inner.kind !== "object") return { mode: "none" };
+    if (scan.inValue) return { mode: scan.inString ? "none" : "keyMapValue", keyMap: "projection" };
+    return { mode: "field" };
+  }
+
+  if (depth === 1) {
+    if (inner.kind !== "object") return { mode: "none" };
+    if (scan.inValue) {
+      if (scan.valueKey === "$meta") return { mode: "enumValue", enumKey: "$meta" };
+      return { mode: "none" };
+    }
+    return { mode: "projectionOperator" };
+  }
+
+  return { mode: "none" };
+}
 
 /** Option keys whose value is a fixed set of strings. */
 const OPTION_VALUE_ENUMS: Record<string, string> = { returnDocument: "returnDocument", validationLevel: "validationLevel", validationAction: "validationAction" };
@@ -1076,10 +1110,13 @@ function classifyMethodOptions(method: string, scan: MongoCallScan): MongoCursor
 
   // Which option's value holds the cursor, however deep.
   const option = scan.stack[1]?.key ?? "";
-  // `{ sort: { … } }` and `{ projection: { … } }` are field maps one level in.
-  if (depth === 1 && inner.kind === "object" && FIELD_MAP_OPTION_KEYS.has(option)) {
+  if (option === "projection") {
+    return { ...classifyKeyMap(scan, 1, "projection"), method };
+  }
+  // `{ sort: { … } }` is a field map one level in.
+  if (depth === 1 && inner.kind === "object" && option === "sort") {
     if (!scan.inValue) return { mode: "field", method };
-    return { mode: scan.inString ? "none" : "keyMapValue", method, keyMap: option };
+    return { mode: scan.inString ? "none" : "keyMapValue", method, keyMap: "sort" };
   }
   if (FILTER_OPTION_KEYS.has(option)) return { ...classifyFilter(scan, 1), method };
   if (option === "arrayFilters") return { ...classifyFilter(scan, 2), method };

apps/desktop/src/lib/mongo/mongoCompletionTables.ts

@@ -16,6 +16,7 @@
  *   QUERY_OPERATORS      → filter documents (`find`, `$match`, …)
  *   UPDATE_OPERATORS     → update documents (`updateOne`, `findOneAndUpdate`, …)
  *   PUSH_MODIFIERS       → the object value of `$push` / `$addToSet`
+ *   PROJECTION_OPERATORS → projection documents (`find`, `findOne`, `findOneAndUpdate`, …)
  *   PIPELINE_STAGES      → elements of an aggregation pipeline array
  *   ACCUMULATORS         → the output fields of `$group`
  *   EXPRESSION_OPERATORS → aggregation expression position (`$project`, `$expr`, …)
@@ -112,6 +113,13 @@ export const PUSH_MODIFIERS: MongoOperatorSpec[] = specs([
   ["$position", "Insert position for $each", "$position: 0"],
 ]);
 
+/** Projection operators, valid inside a projected field's object value in find-style projections. */
+export const PROJECTION_OPERATORS: MongoOperatorSpec[] = specs([
+  ["$slice", "Limits the number of elements projected from an array", "$slice: ${}"],
+  ["$elemMatch", "Projects the first array element matching a condition", "$elemMatch: { ${} }"],
+  ["$meta", "Projects metadata associated with the document", '$meta: "textScore"'],
+]);
+
 export const PIPELINE_STAGES: MongoOperatorSpec[] = specs([
   ["$match", "Filters documents", "$match: { ${} }"],
   ["$project", "Reshapes documents", "$project: { ${} }"],
@@ -494,6 +502,10 @@ export const ENUM_VALUES: Record<string, MongoOperatorSpec[]> = {
     ["s", "Dot matches newlines", '"s"'],
     ["u", "Unicode character classes", '"u"'],
   ]),
+  $meta: specs([
+    ["textScore", "Access the text search score", '"textScore"'],
+    ["indexKey", "Access the index key for the document", '"indexKey"'],
+  ]),
   geometryType: specs([
     ["Point", "Single position", '"Point"'],
     ["LineString", "Sequence of positions", '"LineString"'],

packages/app-tests/mongoCompletion.test.ts

@@ -12,6 +12,7 @@ import {
   METHOD_OPTION_KEYS,
   OPERATOR_SUB_KEYS,
   PIPELINE_STAGES,
+  PROJECTION_OPERATORS,
   PUSH_MODIFIERS,
   QUERY_OPERATORS,
   STAGE_OPTION_KEYS,
@@ -828,6 +829,49 @@ test("every suggested map value parses in the position that offers it", () => {
   }
 });
 
+test("suggests projection operators in find projections", () => {
+  const ops = ["$elemMatch", "$meta", "$slice"];
+  assert.deepEqual(labels("db.users.find({}, { tags: { ", { fields }), ops);
+  assert.deepEqual(labels("db.users.find({}, { tags: { $", { fields }), ops);
+  assert.deepEqual(labels("db.users.findOne({}, { tags: { ", { fields }), ops);
+  assert.deepEqual(labels("db.users.findOneAndUpdate({}, { $set: { a: 1 } }, { projection: { tags: { ", { fields }), ops);
+  assert.deepEqual(labels("db.users.findOneAndDelete({}, { projection: { tags: { ", { fields }), ops);
+
+  // Positional operator form needs nothing new and still completes map values
+  assert.deepEqual(labels('db.users.find({}, { "tags.$": ', { fields }), ["0", "1"]);
+
+  // $slice takes only numbers, so completion offers nothing
+  assert.deepEqual(labels("db.users.find({}, { tags: { $slice: ", { fields }), []);
+  assert.deepEqual(labels("db.users.find({}, { tags: { $slice: [", { fields }), []);
+
+  // $meta value enum in and out of quotes
+  assert.deepEqual(labels('db.users.find({}, { score: { $meta: "', { fields }), ["textScore", "indexKey"]);
+  assert.deepEqual(labels('db.users.find({}, { score: { $meta: "text', { fields }), ["textScore"]);
+  assert.deepEqual(labels("db.users.find({}, { score: { $meta: ", { fields }), ["textScore", "indexKey"]);
+
+  const quotedMeta = buildMongoCompletionItems('db.users.find({}, { score: { $meta: "', 'db.users.find({}, { score: { $meta: "'.length);
+  const unquotedMeta = buildMongoCompletionItems("db.users.find({}, { score: { $meta: ", "db.users.find({}, { score: { $meta: ".length);
+  assert.equal(quotedMeta.find((item) => item.label === "textScore")?.apply, '"textScore"');
+  assert.equal(unquotedMeta.find((item) => item.label === "textScore")?.apply, '"textScore"');
+  assert.equal(getMongoCompletionContext('db.users.find({}, { score: { $meta: "" } })', 'db.users.find({}, { score: { $meta: "'.length).replaceClosingQuote, '"');
+
+  // $elemMatch body completes fields and filter operators
+  assert.deepEqual(labels("db.users.find({}, { tags: { $elemMatch: { ", { fields }).slice(0, 3), ["_id", "createdAt", "name"]);
+  assert.ok(labels("db.users.find({}, { tags: { $elemMatch: { score: { ", { fields }).includes("$gt"));
+  assert.ok(labels("db.users.find({}, { tags: { $elemMatch: { score: { $gt: ", { fields }).includes("NumberInt"));
+});
+
+test("every suggested projection operator parses", () => {
+  const render = (op: { label: string; apply: string }) => {
+    if (op.label === "$elemMatch") return "$elemMatch: { score: 1 }";
+    return op.apply.replace(/\$\{([^{}]*)\}/g, (_, name: string) => name || "1");
+  };
+  for (const op of PROJECTION_OPERATORS) {
+    const command = `db.users.find({}, { tags: { ${render(op)} } })`;
+    assert.ok(parseMongoCommand(command), `${command} must parse`);
+  }
+});
+
 test("offers nothing rather than top-level snippets inside an unmodelled argument", () => {
   // `db.collection.find` is not something that can be typed inside these parentheses, so the
   // top-level snippets are noise there; the engine stays quiet until the argument is modelled.
@@ -1207,6 +1251,7 @@ test("every suggested sub-document key and enumerated value parses in the positi
 
   const valueCommands: Record<string, (value: string) => string> = {
     $type: (value) => `db.users.find({ a: { $type: ${value} } })`,
+    $meta: (value) => `db.users.find({}, { score: { $meta: ${value} } })`,
     bsonType: (value) => `db.users.find({ $jsonSchema: { bsonType: ${value} } })`,
     $options: (value) => `db.users.find({ a: { $regex: "x", $options: ${value} } })`,
     geometryType: (value) => `db.users.find({ loc: { $geoIntersects: { $geometry: { type: ${value}, coordinates: [] } } } })`,
@@ -1385,6 +1430,7 @@ test("snippet templates use placeholder syntax CodeMirror actually honours", ()
     ...QUERY_OPERATORS,
     ...UPDATE_OPERATORS,
     ...PUSH_MODIFIERS,
+    ...PROJECTION_OPERATORS,
     ...PIPELINE_STAGES,
     ...ACCUMULATORS,
     ...WINDOW_OPERATORS,