Parenthesize interpolations containing global::

ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj

@@ -137,6 +137,7 @@
     <Compile Include="TestCases\ILPretty\Issue3442.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />
     <Compile Include="TestCases\Pretty\Comparisons.cs" />
+    <Compile Include="TestCases\Pretty\GloballyQualifiedTypeInStringInterpolation.cs" />
     <Compile Include="TestCases\Pretty\Issue3406.cs" />
     <Compile Include="TestCases\Pretty\PointerArithmetic.cs" />
     <Compile Include="TestCases\Pretty\Issue3439.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -308,6 +308,19 @@ public async Task UsingVariables([ValueSource(nameof(roslyn3OrNewerWithNet40Opti
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task GloballyQualifiedTypeInStringInterpolation([ValueSource(nameof(roslynOnlyWithNet40Options))] CompilerOptions cscOptions)
+		{
+			// https://github.com/icsharpcode/ILSpy/issues/3447
+			await RunForLibrary(
+				cscOptions: cscOptions,
+				configureDecompiler: settings => {
+					settings.UsingDeclarations = false;
+					settings.AlwaysUseGlobal = true;
+				}
+			);
+		}
+
 		[Test]
 		public async Task LiftedOperators([ValueSource(nameof(defaultOptions))] CompilerOptions cscOptions)
 		{

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

@@ -0,0 +1,25 @@
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public static class GloballyQualifiedTypeInStringInterpolation
+	{
+		public static string Root => $"Prefix {(global::System.DateTime.Now)} suffix";
+		public static string Cast => $"Prefix {((int)global::System.DateTime.Now.Ticks)} suffix";
+#if CS100 && NET60
+		public static string Lambda1 => $"Prefix {(() => global::System.DateTime.Now)} suffix";
+#else
+		public static string Lambda1 => $"Prefix {(global::System.Func<global::System.DateTime>)(() => global::System.DateTime.Now)} suffix";
+#endif
+		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

@@ -389,6 +389,38 @@ public override void VisitAsExpression(AsExpression asExpression)
 			base.VisitAsExpression(asExpression);
 		}
 
+		public override void VisitInterpolation(Interpolation interpolation)
+		{
+			// Need to do this first, in case the descendents parenthesize themselves.
+			base.VisitInterpolation(interpolation);
+
+			// If an interpolation contains global::, we need to parenthesize the expression.
+			if (InterpolationNeedsParenthesis(interpolation))
+				Parenthesize(interpolation.Expression);
+
+			static bool InterpolationNeedsParenthesis(AstNode node)
+			{
+				if (node is MemberType { IsDoubleColon: true })
+					return true;
+
+				if (node is ParenthesizedExpression)
+					return false;
+				if (node is AnonymousMethodExpression or LambdaExpression { Body: BlockStatement })
+					return false;
+				if (node is InvocationExpression invocation)
+					return InterpolationNeedsParenthesis(invocation.Target);
+				if (node is CastExpression cast)
+					return InterpolationNeedsParenthesis(cast.Expression);
+
+				foreach (var child in node.Children)
+				{
+					if (InterpolationNeedsParenthesis(child))
+						return true;
+				}
+				return false;
+			}
+		}
+
 		// Conditional operator
 		public override void VisitConditionalExpression(ConditionalExpression conditionalExpression)
 		{