STREAMS-1982: Add singleton compat for MinKey

Author: tcannon91

snippets/mongocompat/mongotypes.js

@@ -714,6 +714,41 @@ if (typeof (gc) == "undefined") {
     };
 }
 
+// MinKey
+if (typeof (MinKey) != "undefined") {
+    const OriginalMinKey = MinKey;
+    MinKey = function () {
+        if (MinKey.prototype.__instance__ === undefined) {
+            MinKey.prototype.__instance__ = new OriginalMinKey();
+        }
+
+        return MinKey.prototype.__instance__;
+    };
+
+    MinKey.prototype = OriginalMinKey.prototype;
+
+    for (const key of Object.getOwnPropertyNames(OriginalMinKey)) {
+        // Skip prototype, length, name(function internals)
+        if (key !== 'prototype' && key !== 'length' && key !== 'name') {
+            MinKey[key] = OriginalMinKey[key];
+        }
+    }
+
+    MinKey.prototype.toJSON = function () {
+        return this.tojson();
+    };
+
+    MinKey.prototype.tojson = function () {
+        return "{ \"$minKey\" : 1 }";
+    };
+
+    MinKey.prototype.toString = function () {
+        return "[object Function]";
+    };
+} else {
+    print("warning: no MinKey class");
+}
+
 // Free Functions
 tojsononeline = function(x) {
     return tojson(x, " ", true);

snippets/mongocompat/test.js

@@ -87,7 +87,7 @@ const tsFromStr = Timestamp.fromString('ff', 16);
 assert.strictEqual(tsFromStr.i, 255);
 assert.strictEqual(tsFromStr.t, 0);
 assert.strictEqual(Timestamp.MAX_VALUE._bsontype, 'Long');
-assert.strictEqual(Timestamp.MAX_VALUE, Long.MAX_UNSIGNED_VALUE); 
+assert.strictEqual(Timestamp.MAX_VALUE, Long.MAX_UNSIGNED_VALUE);
 
 const id = ObjectId('68ffa28b77bba38c9ddcf376');
 const dbRef = DBRef('testColl', id, 'testDb');
@@ -131,3 +131,15 @@ try {
 }
 assert.strictEqual(typeof tojsonObject({ key: "value" }), 'string');
 assert.strictEqual(typeof tojsonObject([1, 2, 3]), 'string');
+
+// Test MinKey
+const minKey = new MinKey();
+assert(minKey instanceof MinKey, "minKey should be an instance of MinKey");
+assert.strictEqual(minKey.tojson(), '{ "$minKey" : 1 }', "minKey should serialize correctly");
+assert.strictEqual(minKey.toString(), "[object Function]", "minKey toString should work");
+assert.strictEqual(minKey.toJSON(), '{ "$minKey" : 1 }', "minKey toJSON should work");
+
+// Test that multiple references return the same instance
+const anotherMinKeyRef = new MinKey();
+assert.strictEqual(minKey, anotherMinKeyRef, "minKey should be a singleton - v1");
+assert.strictEqual(MinKey(), MinKey(), "minKey should be a singleton - v2");