Fix in-memory metadatabase creation in defaultMetadatabase

Sources/SQLiteData/CloudKit/Internal/Metadatabase.swift

@@ -24,7 +24,12 @@
       throw InMemoryDatabase()
     }
 
-    let metadatabase = try DatabasePool(path: url.path(percentEncoded: false))
+    let metadatabase: any DatabaseWriter =
+      if url.isInMemory {
+        try DatabaseQueue(path: url.absoluteString)
+      } else {
+        try DatabasePool(path: url.path(percentEncoded: false))
+      }
     try migrate(metadatabase: metadatabase)
     return metadatabase
   }

Tests/SQLiteDataTests/CloudKitTests/MetadatabaseTests.swift

@@ -0,0 +1,26 @@
+#if canImport(CloudKit)
+  import Foundation
+  import GRDB
+  import OSLog
+  @testable import SQLiteData
+  import Testing
+
+  @Suite struct MetadatabaseTests {
+    @available(iOS 17, macOS 14, tvOS 17, watchOS 10, *)
+    @Test func inMemoryMetadatabase() throws {
+      let url = try URL.metadatabase(databasePath: ":memory:", containerIdentifier: nil)
+      #expect(url.isInMemory)
+
+      let metadatabase = try defaultMetadatabase(
+        logger: Logger(subsystem: "test", category: "test"),
+        url: url
+      )
+      let mainDatabaseFile = try metadatabase.read { db in
+        try String.fetchOne(db, sql: "SELECT file FROM pragma_database_list WHERE name = 'main'")
+      }
+      // NB: SQLite reports an empty file path for in-memory databases. A non-empty path
+      //     means the metadatabase was silently created on disk.
+      #expect(mainDatabaseFile == "")
+    }
+  }
+#endif