Add workaround for decoding NUMERIC as Double

Sources/PostgresKit/PostgresDataTranslation.swift

@@ -42,6 +42,12 @@ struct PostgresDataTranslation {
                 cellToDecode = PostgresCell(bytes: cell.bytes, dataType: .name, format: cell.format, columnName: cell.columnName, columnIndex: cell.columnIndex)
             } else if cell.format == .binary && [.char, .varchar, .text].contains(cell.dataType) && T.self is Decimal.Type { // Workaround cheat for Fluent's assumption that Decimal strings work
                 cellToDecode = PostgresCell(bytes: cell.bytes, dataType: .numeric, format: .text, columnName: cell.columnName, columnIndex: cell.columnIndex)
+            } else if cell.format == .binary && cell.dataType == .numeric && T.self is Double.Type { // Workaround cheat for Fluent's expectation that Postgres's `numeric/decimal` can be decoded as Double
+                // Extremely manual workaround...
+                guard let value = PostgresData(type: cell.dataType, formatCode: cell.format, value: cell.bytes).numeric?.double else {
+                    throw DecodingError.dataCorrupted(.init(codingPath: codingPath, debugDescription: "Invalid numeric value encoding"))
+                }
+                return value as! T
             } else {
                 cellToDecode = cell
             }

Tests/PostgresKitTests/PostgresKitTests.swift

@@ -208,6 +208,22 @@ final class PostgresKitTests: XCTestCase {
         XCTAssertEqual(decoded1.prop3, instance.prop3)
         XCTAssertEqual(decoded2.count, 2)
     }
+
+    func testFluentWorkaroundsDecoding() throws {
+        // SQLKit benchmarks already test enum handling
+
+        // Text encoding for Decimal
+        let decimalBuffer = ByteBuffer(string: Decimal(12345.6789).description)
+        var decimalValue: Decimal?
+        XCTAssertNoThrow(decimalValue = try PostgresDataTranslation.decode(Decimal.self, from: .init(bytes: decimalBuffer, dataType: .numeric, format: .text, columnName: "", columnIndex: -1), in: .default))
+        XCTAssertEqual(decimalValue, Decimal(12345.6789))
+
+        // Decoding Double from NUMERIC
+        let numericBuffer = PostgresData(numeric: .init(decimal: 12345.6789)).value
+        var numericValue: Double?
+        XCTAssertNoThrow(numericValue = try PostgresDataTranslation.decode(Double.self, from: .init(bytes: numericBuffer, dataType: .numeric, format: .binary, columnName: "", columnIndex: -1), in: .default))
+        XCTAssertEqual(numericValue, Double(Decimal(12345.6789).description))
+    }
 
     var eventLoop: any EventLoop { self.eventLoopGroup.any() }
     var eventLoopGroup: (any EventLoopGroup)!