Improvements:

* Cleaner output
* More unit testing
* More efficient tree search

ICSharpCode.Decompiler.Tests/TestCases/Pretty/GloballyQualifiedTypeInStringInterpolation.cs

@@ -2,6 +2,20 @@
 {
 	public static class GloballyQualifiedTypeInStringInterpolation
 	{
-		public static string CurrentDateTime => $"Time: {(global::System.DateTime.Now)}";
+		public static string Root => $"Prefix {(global::System.DateTime.Now)} suffix";
+		public static string Cast => $"Prefix {((int)global::System.DateTime.Now.Ticks)} suffix";
+		public static string Lambda1 => $"Prefix {(global::System.Func<global::System.DateTime>)(() => global::System.DateTime.Now)} suffix";
+		public static string Lambda2 => $"Prefix {((global::System.Func<global::System.DateTime>)(() => global::System.DateTime.Now))()} suffix";
+		public static string Method1 => $"Prefix {M(global::System.DateTime.Now)} suffix";
+		public static string Method2 => $"Prefix {(global::System.DateTime.Now.Ticks)} suffix";
+		public static string Method3 => $"Prefix {(global::System.DateTime.Equals(global::System.DateTime.Now, global::System.DateTime.Now))} suffix";
+		public static string ConditionalExpression1 => $"Prefix {(Boolean ? global::System.DateTime.Now : global::System.DateTime.UtcNow)} suffix";
+		public static string ConditionalExpression2 => $"Prefix {(Boolean ? global::System.DateTime.Now : global::System.DateTime.UtcNow).Ticks} suffix";
+
+		private static bool Boolean => false;
+		private static long M(global::System.DateTime time)
+		{
+			return time.Ticks;
+		}
 	}
 }

ICSharpCode.Decompiler/CSharp/OutputVisitor/InsertParenthesesVisitor.cs

@@ -393,9 +393,31 @@ namespace ICSharpCode.Decompiler.CSharp.OutputVisitor
 		public override void VisitInterpolation(Interpolation interpolation)
 		{
 			// If an interpolation contains global::, we need to parenthesize the expression.
-			if (interpolation.Descendants.Any(n => n is MemberType { IsDoubleColon: true }))
+			if (InterpolationNeedsParenthesized(interpolation))
 				Parenthesize(interpolation.Expression);
 			base.VisitInterpolation(interpolation);
+
+			static bool InterpolationNeedsParenthesized(AstNode node)
+			{
+				if (node is MemberType { IsDoubleColon: true })
+					return true;
+
+				if (node is ConditionalExpression)
+					return false; // Conditional expressions are parenthesized in their own visit method.
+				if (node is AnonymousMethodExpression or LambdaExpression)
+					return false;
+				if (node is InvocationExpression invocation)
+					return InterpolationNeedsParenthesized(invocation.Target);
+				if (node is CastExpression cast)
+					return InterpolationNeedsParenthesized(cast.Expression);
+
+				foreach (var child in node.Children)
+				{
+					if (InterpolationNeedsParenthesized(child))
+						return true;
+				}
+				return false;
+			}
 		}
 
 		// Conditional operator