Refactor: Extract ensureMinimumSpanSize helper function

Extracted the logic for ensuring minimum span size into a helper function to reduce code duplication and improve maintainability.

Addressed code review feedback.

Co-authored-by: jakebailey <[email protected]>

Author: Copilot

internal/ls/signaturehelp.go

@@ -1070,23 +1070,29 @@ func getApplicableSpanForArguments(argumentList *ast.NodeList, node *ast.Node, s
 		spanStart := node.End()
 		spanEnd := scanner.SkipTrivia(sourceFile.Text(), node.End())
 		// Ensure the span includes at least the position right after the opening paren
-		if spanEnd <= spanStart {
-			spanEnd = spanStart + 1
-		}
+		spanEnd = ensureMinimumSpanSize(spanStart, spanEnd)
 		return core.NewTextRange(spanStart, spanEnd)
 	}
 	applicableSpanStart := argumentList.Pos()
 	applicableSpanEnd := scanner.SkipTrivia(sourceFile.Text(), argumentList.End())
 
 	// If the argument list is empty (Pos == End), extend the span to include at least
 	// one position. This handles foo(|) where the cursor is right after the opening paren.
-	if applicableSpanEnd <= applicableSpanStart {
-		applicableSpanEnd = applicableSpanStart + 1
-	}
+	applicableSpanEnd = ensureMinimumSpanSize(applicableSpanStart, applicableSpanEnd)
 
 	return core.NewTextRange(applicableSpanStart, applicableSpanEnd)
 }
 
+// ensureMinimumSpanSize ensures that a span includes at least one position.
+// This is necessary for empty argument lists where start == end would create
+// a span that doesn't contain any position.
+func ensureMinimumSpanSize(start, end int) int {
+	if end <= start {
+		return start + 1
+	}
+	return end
+}
+
 type argumentOrParameterListAndIndex struct {
 	list          *ast.NodeList
 	argumentIndex int