Introduce dedicated interface for branches in $switch

Author: alcaeus

generator/config/expression/case.yaml

@@ -2,7 +2,7 @@
 name: $case
 link: 'https://www.mongodb.com/docs/manual/reference/operator/aggregation/switch/'
 type:
-    - resolvesToAny
+    - switchBranch
 encode: flat_object
 description: |
     Represents a single case in a $switch expression

generator/config/expressions.php

@@ -113,6 +113,10 @@
         'returnType' => Type\GeometryInterface::class,
         'acceptedTypes' => [Type\GeometryInterface::class, ...$bsonTypes['object']],
     ],
+    'switchBranch' => [
+        'returnType' => Type\SwitchBranchInterface::class,
+        'acceptedTypes' => [Type\SwitchBranchInterface::class, ...$bsonTypes['object']],
+    ],
 
     // @todo add enum values
     'Granularity' => [

generator/config/schema.json

@@ -29,6 +29,7 @@
                             "filter",
                             "window",
                             "geometry",
+                            "switchBranch",
                             "resolvesToAny",
                             "resolvesToNumber",
                             "resolvesToDouble",

src/Builder/Expression/CaseOperator.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace MongoDB\Builder\Type;
+
+/**
+ * Interface for branches in $switch operators
+ *
+ * @see https://www.mongodb.com/docs/manual/reference/operator/aggregation/switch/
+ */
+interface SwitchBranchInterface
+{
+}