Adds DateTime conversion analyzer tests

Adds tests for implicit DateTime to DateTimeOffset conversion analyzer.

These tests cover scenarios such as implicit conversions in property
comparisons inside lambdas, expression tree lambdas, nullable DateTime
to nullable DateTimeOffset assignments, and method return statements.

Also adds missing references to DiagnosticVerifier to enable the tests.

Author: BenjaminMichaelis

IntelliTect.Analyzer/IntelliTect.Analyzer.Test/DateTimeConversionTests.cs

@@ -205,6 +205,140 @@ static void Main(string[] args)
 
         }
 
+        [TestMethod]
+        public void ImplicitConversionInPropertyComparisonInsideLambda_ProducesWarningMessage()
+        {
+            string source = @"
+using System;
+
+namespace ConsoleApp53
+{
+    class TimeEntry
+    {
+        public DateTimeOffset EndDate { get; set; }
+    }
+
+    class Program
+    {
+        static DateTimeOffset EndDate { get; set; }
+
+        static void Main(string[] args)
+        {
+            TimeEntry entry = new TimeEntry();
+            Func<bool> check = () => entry.EndDate <= EndDate.Date.AddDays(1).AddTicks(-1);
+        }
+    }
+}";
+
+            VerifyCSharpDiagnostic(source,
+                           new DiagnosticResult
+                           {
+                               Id = "INTL0202",
+                               Severity = DiagnosticSeverity.Warning,
+                               Message = "Using 'DateTimeOffset.implicit operator DateTimeOffset(DateTime)' or 'new DateTimeOffset(DateTime)' can result in unpredictable behavior",
+                               Locations =
+                                   [
+                            new DiagnosticResultLocation("Test0.cs", 18, 55)
+                                   ]
+                           });
+        }
+
+        [TestMethod]
+        public void ImplicitConversionInExpressionTreeLambda_ProducesWarningMessage()
+        {
+            string source = @"
+using System;
+using System.Linq.Expressions;
+
+namespace ConsoleApp54
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Expression<Func<DateTimeOffset, bool>> expr = dto => dto > DateTime.Now;
+        }
+    }
+}";
+
+            VerifyCSharpDiagnostic(source,
+                           new DiagnosticResult
+                           {
+                               Id = "INTL0202",
+                               Severity = DiagnosticSeverity.Warning,
+                               Message = "Using 'DateTimeOffset.implicit operator DateTimeOffset(DateTime)' or 'new DateTimeOffset(DateTime)' can result in unpredictable behavior",
+                               Locations =
+                                   [
+                            new DiagnosticResultLocation("Test0.cs", 11, 72)
+                                   ]
+                           });
+        }
+
+        [TestMethod]
+        public void NullableDateTimeToNullableDateTimeOffsetAssignment_ProducesWarningMessage()
+        {
+            string source = @"
+using System;
+
+namespace ConsoleApp55
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            DateTime? dt = DateTime.Now;
+            DateTimeOffset? dto = dt;
+        }
+    }
+}";
+
+            VerifyCSharpDiagnostic(source,
+                           new DiagnosticResult
+                           {
+                               Id = "INTL0202",
+                               Severity = DiagnosticSeverity.Warning,
+                               Message = "Using 'DateTimeOffset.implicit operator DateTimeOffset(DateTime)' or 'new DateTimeOffset(DateTime)' can result in unpredictable behavior",
+                               Locations =
+                                   [
+                            new DiagnosticResultLocation("Test0.cs", 11, 35)
+                                   ]
+                           });
+        }
+
+        [TestMethod]
+        public void ImplicitConversionInMethodReturnStatement_ProducesWarningMessage()
+        {
+            string source = @"
+using System;
+
+namespace ConsoleApp57
+{
+    class Program
+    {
+        static DateTimeOffset GetDateTimeOffset()
+        {
+            return DateTime.Now;
+        }
+
+        static void Main(string[] args)
+        {
+        }
+    }
+}";
+
+            VerifyCSharpDiagnostic(source,
+                           new DiagnosticResult
+                           {
+                               Id = "INTL0202",
+                               Severity = DiagnosticSeverity.Warning,
+                               Message = "Using 'DateTimeOffset.implicit operator DateTimeOffset(DateTime)' or 'new DateTimeOffset(DateTime)' can result in unpredictable behavior",
+                               Locations =
+                                   [
+                            new DiagnosticResultLocation("Test0.cs", 10, 20)
+                                   ]
+                           });
+        }
+
         protected override DiagnosticAnalyzer GetCSharpDiagnosticAnalyzer()
         {
             return new Analyzers.BanImplicitDateTimeToDateTimeOffsetConversion();

IntelliTect.Analyzer/IntelliTect.Analyzer.Test/Helpers/DiagnosticVerifier.Helper.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
+using System.Linq.Expressions;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.Diagnostics;
@@ -19,6 +20,7 @@ public abstract partial class DiagnosticVerifier
         private static readonly MetadataReference _SystemCoreReference = MetadataReference.CreateFromFile(typeof(Enumerable).Assembly.Location);
         private static readonly MetadataReference _CSharpSymbolsReference = MetadataReference.CreateFromFile(typeof(CSharpCompilation).Assembly.Location);
         private static readonly MetadataReference _CodeAnalysisReference = MetadataReference.CreateFromFile(typeof(Compilation).Assembly.Location);
+        private static readonly MetadataReference _LinqExpressionsReference = MetadataReference.CreateFromFile(typeof(Expression<>).Assembly.Location);
 
         internal static string DefaultFilePathPrefix = "Test";
         internal static string CSharpDefaultFileExt = "cs";
@@ -158,7 +160,8 @@ private static Project CreateProject(string[] sources, string language = Languag
                     .AddMetadataReference(projectId, _CorlibReference)
                     .AddMetadataReference(projectId, _SystemCoreReference)
                     .AddMetadataReference(projectId, _CSharpSymbolsReference)
-                    .AddMetadataReference(projectId, _CodeAnalysisReference);
+                    .AddMetadataReference(projectId, _CodeAnalysisReference)
+                    .AddMetadataReference(projectId, _LinqExpressionsReference);
             }
 
             int count = 0;