fix: MagicNumberStringMacro to support custom parsing argument

Author: kkazuha7

Sources/BinaryParsingMacros/MagicNumberStringMacro.swift

@@ -51,9 +51,14 @@ public struct MagicNumberStringMacro: ExpressionMacro {
       return ""
     }
 
+    var parsingExpr = "input"
+    if let parsingArg = node.arguments.first(where: { $0.label?.text == "parsing" }) {
+      parsingExpr = parsingArg.expression.description
+    }
+
     return """
       _loadAndCheckDirectBytes(\
-      parsing: &input, \
+      parsing: \(raw: parsingExpr), \
       bigEndianValue: 0x\(raw: String(integerValue, radix: 16)) as \(raw: integerType))
       """
   }

Tests/BinaryParsingMacrosTests/ParserMacroTests.swift

@@ -20,9 +20,9 @@ struct StringifyMacroSwiftTestingTests {
   @Test
   func magicNumberString() {
     assertMacro {
-      #"try #magicNumber("qoif", parsing: &input)"#
+      #"try #magicNumber("qoif", parsing: &data)"#
     } expansion: {
-      "try _loadAndCheckDirectBytes(parsing: &input, bigEndianValue: 0x716f6966 as UInt32)"
+      "try _loadAndCheckDirectBytes(parsing: &data, bigEndianValue: 0x716f6966 as UInt32)"
     }
   }
 }