Merge pull request #18431 from CyrusNajmabadi/useThrowExplicitConversion

Don't offer 'use throw expression' when there is an explicit cast in source.  It may change semantics.

src/EditorFeatures/CSharpTest/UseThrowExpression/UseThrowExpressionTests.cs

@@ -324,6 +324,40 @@ void Foo()
             _s = s;
         };
     }
+}");
+        }
+
+        [WorkItem(404142, "https://devdiv.visualstudio.com/DevDiv/_workitems?id=404142")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseThrowExpression)]
+        public async Task TestNotWithAsCheck()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"using System;
+
+class BswParser3
+{
+    private ParserSyntax m_syntax;
+
+    public BswParser3(ISyntax syntax)
+    {
+        if (syntax == null)
+        {
+            [|throw|] new ArgumentNullException(nameof(syntax));
+        }
+
+        m_syntax = syntax as ParserSyntax;
+
+        if (m_syntax == null)
+            throw new ArgumentException();
+    }
+}
+
+internal class ParserSyntax
+{
+}
+
+public interface ISyntax
+{
 }");
         }
     }

src/Features/Core/Portable/UseThrowExpression/AbstractUseThrowExpressionDiagnosticAnalyzer.cs

@@ -233,8 +233,7 @@ private void AnalyzeOperation(OperationAnalysisContext context, INamedTypeSymbol
             localOrParameter = null;
 
             var condition = ifStatement.Condition;
-            var binaryOperator = condition as IBinaryOperatorExpression;
-            if (binaryOperator == null)
+            if (!(condition is IBinaryOperatorExpression binaryOperator))
             {
                 return false;
             }
@@ -262,21 +261,18 @@ private void AnalyzeOperation(OperationAnalysisContext context, INamedTypeSymbol
         private bool TryGetLocalOrParameterSymbol(
             IOperation operation, out ISymbol localOrParameter)
         {
-            if (operation.Kind == OperationKind.ConversionExpression)
+            if (operation is IConversionExpression conversion && !conversion.IsExplicit)
             {
-                var conversionExpression = (IConversionExpression)operation;
-                return TryGetLocalOrParameterSymbol(
-                    conversionExpression.Operand, out localOrParameter);
+                return TryGetLocalOrParameterSymbol(conversion.Operand, out localOrParameter);
             }
-
-            if (operation.Kind == OperationKind.LocalReferenceExpression)
+            else if (operation is ILocalReferenceExpression localReference)
             {
-                localOrParameter = ((ILocalReferenceExpression)operation).Local;
+                localOrParameter = localReference.Local;
                 return true;
             }
-            else if (operation.Kind == OperationKind.ParameterReferenceExpression)
+            else if (operation is IParameterReferenceExpression parameterReference)
             {
-                localOrParameter = ((IParameterReferenceExpression)operation).Parameter;
+                localOrParameter = parameterReference.Parameter;
                 return true;
             }