improved readability & added explanation comment

Author: vinu-vanjari

Sources/SwiftSyntaxMacroExpansion/MacroSystem.swift

@@ -132,16 +132,23 @@ private func expandFreestandingExpr(
 /// Adds the appropriate indentation on expanded code even if it's multi line.
 /// Makes sure original macro expression's trivia is maintained by adding it to expanded code.
 private func adjustIndentationOfFreestandingMacro(expandedCode: String, node: some FreestandingMacroExpansionSyntax) -> String {
-  let indentationOfFirstLine = node.indentationOfFirstLine
-
-  var indentedSource =
-    expandedCode
-    .indented(by: indentationOfFirstLine)
-
-  if indentedSource.count >= indentationOfFirstLine.sourceLength.utf8Length {
-    indentedSource.removeFirst(indentationOfFirstLine.sourceLength.utf8Length)
+  
+  if expandedCode.isEmpty {
+    return expandedCode.wrappingInTrivia(from: node)
   }
-
+  
+  let indentationOfFirstLine = node.indentationOfFirstLine
+  let indentLength = indentationOfFirstLine.sourceLength.utf8Length
+  
+  // we are doing 3 step adjustment here
+  // step 1: add indentation to each line of expanded code
+  // step 2: remove indentation from first line of expaned code
+  // step 3: wrap the expanded code into macro expression's trivia. This trivia will contain appropriate existing
+  // indentation. Note that if macro expression occurs in middle of the line then there will be no indentation or extra space.
+  // Hence we are doing step 2
+  
+  var indentedSource = expandedCode.indented(by: indentationOfFirstLine)
+  indentedSource.removeFirst(indentLength)
   indentedSource = indentedSource.wrappingInTrivia(from: node)
 
   return indentedSource