Improvements to for loop with missing semantic info - fixes #482

Author: GrahamTheCoder

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 * Improve multi-declaration field conversion for arrrays - [#559](https://github.com/icsharpcode/CodeConverter/issues/559)
 * Add parentheses around ternary statement - [#565](https://github.com/icsharpcode/CodeConverter/issues/565)
 * When converting ForEach loop, avoid duplicate variable compilation issue [#558](https://github.com/icsharpcode/CodeConverter/issues/558)
+* Improvements to for loop with missing semantic info - [#482](https://github.com/icsharpcode/CodeConverter/issues/482)
 
 ### C# -> VB
 

CodeConverter/CSharp/MethodBodyExecutableStatementVisitor.cs

@@ -462,7 +462,8 @@ public override async Task<SyntaxList<StatementSyntax>> VisitForBlock(VBSyntax.F
             VariableDeclarationSyntax declaration = null;
             ExpressionSyntax id;
             var controlVarOp = _semanticModel.GetOperation(stmt.ControlVariable) as IVariableDeclaratorOperation;
-            var controlVarType = controlVarOp?.Symbol.Type;
+            var controlVarSymbol = controlVarOp?.Symbol;
+            var controlVarType = controlVarSymbol?.Type;
             var initializers = new List<ExpressionSyntax>();
             if (stmt.ControlVariable is VBSyntax.VariableDeclaratorSyntax) {
                 var v = (VBSyntax.VariableDeclaratorSyntax)stmt.ControlVariable;
@@ -471,9 +472,14 @@ public override async Task<SyntaxList<StatementSyntax>> VisitForBlock(VBSyntax.F
                 id = SyntaxFactory.IdentifierName(declaration.Variables[0].Identifier);
             } else {
                 id = (ExpressionSyntax) await stmt.ControlVariable.AcceptAsync(_expressionVisitor);
-                var controlVarSymbol = controlVarOp?.Symbol;
+
+                // If missing semantic info, the compiler just guesses object. In this branch there was no explicit type, so let's try to improve on that guess:
+                var bestType = controlVarType.Yield()
+                    .Concat(new[] { stmt.FromValue, stmt.ToValue, stmt.StepClause?.StepValue }.Select(exp => _semanticModel.GetTypeInfo(exp).Type))
+                    .FirstOrDefault(t => t != null && t.SpecialType != SpecialType.System_Object);
+
                 if (controlVarSymbol != null && controlVarSymbol.DeclaringSyntaxReferences.Any(r => r.Span.OverlapsWith(stmt.ControlVariable.Span))) {
-                    declaration = CommonConversions.CreateVariableDeclarationAndAssignment(controlVarSymbol.Name, startValue, CommonConversions.GetTypeSyntax(controlVarType));
+                    declaration = CommonConversions.CreateVariableDeclarationAndAssignment(controlVarSymbol.Name, startValue, CommonConversions.GetTypeSyntax(bestType));
                 } else {
                     startValue = SyntaxFactory.AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, id, startValue);
                     initializers.Add(startValue);

CodeConverter/Util/EnumerableExtensions.cs

@@ -77,6 +77,18 @@ public static T OnlyOrDefault<T>(this IEnumerable<T> source, Func<T, bool> predi
             return count == 1 ? previous : default(T);
         }
 
+        public static T SelectFirst<T>(this IEnumerable<T> source, Func<T, bool> predicate = null)
+        {
+            if (predicate != null) source = source.Where(predicate);
+            T previous = default(T);
+            int count = 0;
+            foreach (var element in source) {
+                previous = element;
+                if (++count > 1) return default(T);
+            }
+            return count == 1 ? previous : default(T);
+        }
+
         public static IEnumerable<T> Yield<T>(this T singleElement)
         {
             yield return singleElement;

Tests/CSharp/MissingSemanticModelInfo/ExpressionTests.cs

@@ -32,6 +32,7 @@ private void TestMethod()
 1 target compilation errors:
 CS0234: The type or namespace name 'Some' does not exist in the namespace 'System' (are you missing an assembly reference?)");
         }
+
         [Fact]
         public async Task InvokeMethodWithUnknownReturnTypeAsync()
         {

Tests/CSharp/MissingSemanticModelInfo/StatementTests.cs

@@ -0,0 +1,41 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using ICSharpCode.CodeConverter.Tests.TestRunners;
+using Xunit;
+
+namespace ICSharpCode.CodeConverter.Tests.CSharp.MissingSemanticModelInfo
+{
+    public class StatementTests : ConverterTestBase
+    {
+        [Fact]
+        public async Task MissingLoopTypeAsync()
+        {
+            await TestConversionVisualBasicToCSharpAsync(@"Class MissingLoopType
+    Public Sub Test()
+        Dim x As Asadf = Nothing
+
+        For i = 1 To x.SomeInteger
+
+        Next
+    End Sub
+End Class", @"
+internal partial class MissingLoopType
+{
+    public void Test()
+    {
+        Asadf x = default;
+        for (int i = 1, loopTo = x.SomeInteger; i <= loopTo; i++)
+        {
+        }
+    }
+}
+1 source compilation errors:
+BC30002: Type 'Asadf' is not defined.
+1 target compilation errors:
+CS0246: The type or namespace name 'Asadf' could not be found (are you missing a using directive or an assembly reference?)", missingSemanticInfo: true);
+        }
+    }
+}

Tests/CSharp/StatementTests/LoopStatementTests.cs

@@ -379,6 +379,41 @@ public void PrintLoop(int startIndex, int endIndex, int step)
 }");
         }
 
+        [Fact]
+        public async Task ForEnumAsync()
+        {
+            await TestConversionVisualBasicToCSharpAsync(@"Friend Enum MyEnum
+    Zero,
+    One
+End Enum
+
+Friend Class ForEnumAsync
+    Sub PrintLoop(startIndex As MyEnum, endIndex As MyEnum, [step] As MyEnum)
+      For i = startIndex To endIndex Step [step]
+        Debug.WriteLine(i)
+      Next
+      For i2 As MyEnum = startIndex To endIndex Step [step]
+        Debug.WriteLine(i2)
+      Next
+      For i3 As MyEnum = startIndex To endIndex Step 3
+        Debug.WriteLine(i3)
+      Next
+      For i4 As MyEnum = startIndex To 4
+        Debug.WriteLine(i4)
+      Next
+    End Sub
+End Class", @"using System.Diagnostics;
+
+internal partial class ForEnumAsync
+{
+    public void PrintLoop(int startIndex, int endIndex, int step)
+    {
+        for (int i = startIndex, loopTo = endIndex; step >= 0 ? i <= loopTo : i >= loopTo; i += step)
+            Debug.WriteLine(i);
+    }
+}");
+        }
+
         [Fact]
         public async Task ForeachWithObjectCollectionAsync()
         {