Change IDiagnosticsWriter to implement IDisposable

cpp/autobuilder/Semmle.Autobuild.Cpp.Tests/BuildScripts.cs

@@ -203,6 +203,8 @@ namespace Semmle.Autobuild.Cpp.Tests
         public IList<DiagnosticMessage> Diagnostics { get; } = new List<DiagnosticMessage>();
 
         public void AddEntry(DiagnosticMessage message) => this.Diagnostics.Add(message);
+
+        public void Dispose() { }
     }
 
     /// <summary>

csharp/autobuilder/Semmle.Autobuild.CSharp.Tests/BuildScripts.cs

@@ -218,6 +218,8 @@ namespace Semmle.Autobuild.CSharp.Tests
         public IList<DiagnosticMessage> Diagnostics { get; } = new List<DiagnosticMessage>();
 
         public void AddEntry(DiagnosticMessage message) => this.Diagnostics.Add(message);
+
+        public void Dispose() { }
     }
 
     /// <summary>

csharp/autobuilder/Semmle.Autobuild.Shared/Autobuilder.cs

@@ -361,7 +361,7 @@ namespace Semmle.Autobuild.Shared
         {
             if (disposing)
             {
-                (diagnostics as IDisposable)?.Dispose();
+                diagnostics.Dispose();
             }
         }
 

csharp/extractor/Semmle.Util/ToolStatusPage.cs

@@ -183,7 +183,7 @@ namespace Semmle.Util
     /// <summary>
     /// Provides the ability to write diagnostic messages to some output.
     /// </summary>
-    public interface IDiagnosticsWriter
+    public interface IDiagnosticsWriter : IDisposable
     {
         /// <summary>
         /// Adds <paramref name="message" /> as a new diagnostics entry.