Convert DateAndTime to DateTime

Some things like DateString and setting the system time won't work, but we can always add more special cases later

ICSharpCode.CodeConverter/CSharp/CompilationErrorFixer.cs

@@ -48,8 +48,16 @@ namespace ICSharpCode.CodeConverter.CSharp
                 .Select(d => compilationUnitSyntax.FindNode(d.Location.SourceSpan))
                 .OfType<UsingDirectiveSyntax>()
                 .ToList();
-            if (diagnostics.All(d => d.Id != UnresolvedTypeOrNamespaceDiagnosticId) && unusedUsings.Any()) {
-                compilationUnitSyntax = compilationUnitSyntax.RemoveNodes(unusedUsings, SyntaxRemoveOptions.KeepNoTrivia);
+
+            var nodesWithUnresolvedTypes = diagnostics
+                .Where(d => d.Id == UnresolvedTypeOrNamespaceDiagnosticId && d.Location.IsInSource)
+                .Select(d => compilationUnitSyntax.FindNode(d.Location.SourceSpan))
+                .ToLookup(d => d.GetAncestor<UsingDirectiveSyntax>());
+            unusedUsings = unusedUsings.Except(nodesWithUnresolvedTypes.Select(g => g.Key)).ToList();
+
+            if (!nodesWithUnresolvedTypes[null].Any() && unusedUsings.Any()) {
+                compilationUnitSyntax =
+                    compilationUnitSyntax.RemoveNodes(unusedUsings, SyntaxRemoveOptions.KeepNoTrivia);
             }
 
             return compilationUnitSyntax;

ICSharpCode.CodeConverter/CSharp/NodesVisitor.cs

@@ -1549,7 +1549,7 @@ namespace ICSharpCode.CodeConverter.CSharp
                         // CSharp allows partial qualification within the current type's parent namespace
                         qualifiedName = qualifiedName.Substring(firstMatch.Length);
                     }
-                    else if (!targetSymbolInfo.IsNamespace() && _importedNamespaces.ContainsKey(typeOrNamespace))
+                    else if (!targetSymbolInfo.IsNamespace() && _importedNamespaces.ContainsKey(typeOrNamespace) && qualifiedName.StartsWith(typeOrNamespace))
                     {
                         // An import matches the entire namespace, which means it's not a partially qualified thing that would need extra help in CSharp
                         qualifiedName = qualifiedName.Substring(typeOrNamespace.Length + 1);

ICSharpCode.CodeConverter/Util/ISymbolExtensions.cs

@@ -11,6 +11,8 @@ namespace ICSharpCode.CodeConverter.Util
 #endif
     static class ISymbolExtensions
     {
+        private static readonly string[] TypesToConvertToDateTime = new[] {"DateTime", "DateAndTime" };
+
         /// <summary>
         /// Checks if 'symbol' is accessible from within 'within'.
         /// </summary>
@@ -181,16 +183,41 @@ namespace ICSharpCode.CodeConverter.Util
 
         public static string ToMinimalCSharpDisplayString(this ISymbol symbol, SemanticModel vbSemanticModel, int position, SymbolDisplayFormat format = null)
         {
-            var output = symbol.ToMinimalDisplayString(vbSemanticModel, position, format);
-            if (symbol is ITypeSymbol && output == "Date") return "DateTime";
-            return output;
+            if (TryGetSpecialVBTypeConversion(symbol, out var cSharpDisplayString)) return cSharpDisplayString;
+            return symbol.ToMinimalDisplayString(vbSemanticModel, position, format);
         }
 
         public static string ToCSharpDisplayString(this ISymbol symbol, SymbolDisplayFormat format = null)
         {
-            var output = symbol.ToDisplayString(format);
-            if (symbol is ITypeSymbol && output == "Date") return "DateTime";
-            return output;
+            if (TryGetSpecialVBTypeConversion(symbol, out var cSharpDisplayString)) return cSharpDisplayString;
+
+            return symbol.ToDisplayString(format);
+        }
+
+        private static bool TryGetSpecialVBTypeConversion(ISymbol symbol, out string cSharpDisplayString)
+        {
+            var containingNamespace = symbol?.ContainingNamespace?.ToDisplayString(SymbolDisplayFormat.CSharpErrorMessageFormat);
+            if (containingNamespace == "Microsoft.VisualBasic" || containingNamespace == "System") {
+                if (symbol is ITypeSymbol && TypesToConvertToDateTime.Contains(symbol.Name)) {
+                    {
+                        cSharpDisplayString = "DateTime";
+                        return true;
+                    }
+                } else if (TypesToConvertToDateTime.Contains(symbol.ContainingType?.Name)) {
+                    {
+                        cSharpDisplayString = "DateTime" + "." + symbol.Name;
+                        return true;
+                    }
+                }
+            }
+
+            cSharpDisplayString = null;
+            return false;
+        }
+
+        private static bool ShouldConvertToDateTime(ITypeSymbol symbol, string fullName)
+        {
+            return TypesToConvertToDateTime.Contains(symbol.ToDisplayString(SymbolDisplayFormat.CSharpErrorMessageFormat));
         }
 
         public static bool IsPartialImplementation(this ISymbol declaredSymbol)

Tests/CSharp/NamespaceLevelTests.cs

@@ -54,19 +54,7 @@ public class Test
         {
             TestConversionVisualBasicToCSharp(
                 @"Imports UnrecognizedNamespace",
-                @"using System;
-using System.Collections.Generic;
-using System.Diagnostics;
-using System.Globalization;
-using System.IO;
-using System.Linq;
-using System.Reflection;
-using System.Runtime.CompilerServices;
-using System.Security;
-using System.Text;
-using System.Threading.Tasks;
-using Microsoft.VisualBasic;
-using UnrecognizedNamespace;");
+                @"using UnrecognizedNamespace;");
         }
 
         [Fact]