Add failing test and test infrastructure adjustments to allow compiling referenced assemblies in one go.

ICSharpCode.Decompiler.Tests/Helpers/Tester.cs

@@ -489,6 +489,17 @@ namespace System.Runtime.CompilerServices
 			{
 				sourceFileNames.Add(Path.GetFullPath(Path.Combine(Path.GetDirectoryName(sourceFileName), match.Groups[1].Value)));
 			}
+
+			List<string> dependencyAssemblies = new List<string>();
+			string sourceText = File.ReadAllText(sourceFileName);
+			foreach (Match match in Regex.Matches(sourceText, @"//\s*#dependency\s+([\w\d./\\]+)"))
+			{
+				string depSourcePath = Path.GetFullPath(Path.Combine(
+					Path.GetDirectoryName(sourceFileName), match.Groups[1].Value));
+				var depResults = await CompileCSharp(depSourcePath, flags | CompilerOptions.Library).ConfigureAwait(false);
+				dependencyAssemblies.Add(Path.GetFullPath(depResults.PathToAssembly));
+			}
+
 			bool targetNet40 = (flags & CompilerOptions.TargetNet40) != 0;
 			bool useRoslyn = (flags & CompilerOptions.UseRoslynMask) != 0;
 
@@ -556,6 +567,11 @@ namespace System.Runtime.CompilerServices
 
 				references = references.Select(r => "-r:\"" + Path.Combine(refAsmPath, r) + "\"");
 
+				foreach (var dependency in dependencyAssemblies)
+				{
+					references = references.Append($"-r:\"{dependency}\"");
+				}
+
 				string otherOptions = $"-nologo -noconfig " +
 					$"-langversion:{languageVersion} " +
 					$"-unsafe -o{(flags.HasFlag(CompilerOptions.Optimize) ? "+ " : "- ")}";

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

@@ -167,6 +167,8 @@
     <Compile Include="TestCases\Pretty\Issue3610.cs" />
     <Compile Include="TestCases\Pretty\Issue3611.cs" />
     <Compile Include="TestCases\Pretty\Issue3598.cs" />
+    <None Include="TestCases\Pretty\Issue3684.dep.cs" />
+    <None Include="TestCases\Pretty\Issue3684.cs" />
     <None Include="TestCases\Ugly\NoLocalFunctions.Expected.cs" />
     <None Include="TestCases\ILPretty\Issue3504.cs" />
     <Compile Include="TestCases\ILPretty\MonoFixed.cs" />

ICSharpCode.Decompiler.Tests/PrettyTestRunner.cs

@@ -852,6 +852,12 @@ namespace ICSharpCode.Decompiler.Tests
 			await RunForLibrary(cscOptions: cscOptions);
 		}
 
+		[Test]
+		public async Task Issue3684([ValueSource(nameof(roslyn4OrNewerOptions))] CompilerOptions cscOptions)
+		{
+			await RunForLibrary(cscOptions: cscOptions);
+		}
+
 		async Task RunForLibrary([CallerMemberName] string testName = null, AssemblerOptions asmOptions = AssemblerOptions.None, CompilerOptions cscOptions = CompilerOptions.None, Action<DecompilerSettings> configureDecompiler = null)
 		{
 			await Run(testName, asmOptions | AssemblerOptions.Library, cscOptions | CompilerOptions.Library, configureDecompiler);

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Issue3684.cs

@@ -0,0 +1,21 @@
+// #dependency Issue3684.dep.cs
+using CrossAssemblyDep;
+
+namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
+{
+	public static class Issue3684
+	{
+		public interface IInterface
+		{
+			string Name { get; set; }
+		}
+
+		public class DerivedClass : BaseClass, IInterface
+		{
+			T IInterface.Convert<T>(T input)
+			{
+				return ((BaseClass)this).Convert<T>(input);
+			}
+		}
+	}
+}

ICSharpCode.Decompiler.Tests/TestCases/Pretty/Issue3684.dep.cs

@@ -0,0 +1,16 @@
+namespace CrossAssemblyDep
+{
+	public class BaseClass
+	{
+		private string name = "BaseClass";
+
+		public string Name {
+			get {
+				return name;
+			}
+			set {
+				name = value;
+			}
+		}
+	}
+}