Merge pull request #18679 from CyrusNajmabadi/useThrowElseClause

Don't offer to convert an 'if' to a 'throw expressoin' if there is an 'else clause'

src/EditorFeatures/CSharpTest/UseThrowExpression/UseThrowExpressionTests.cs

@@ -358,6 +358,34 @@ internal class ParserSyntax
 
 public interface ISyntax
 {
+}");
+        }
+
+        [WorkItem(18670, "https://github.com/dotnet/roslyn/issues/18670")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseThrowExpression)]
+        public async Task TestNotWithElseClause()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+using System;
+
+class C
+{
+    int? _x;
+
+    public C(int? x)
+    {
+        if (x == null)
+        {
+            [|throw|] new ArgumentNullException(nameof(x));
+        }
+        else
+        {
+            Console.WriteLine();
+        }
+
+        _x = x;
+    }
 }");
         }
     }

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

@@ -110,6 +110,12 @@ private void AnalyzeOperation(OperationAnalysisContext context, INamedTypeSymbol
                 return;
             }
 
+            if (ifOperation.IfFalseStatement != null)
+            {
+                // Can't offer this if the 'if-statement' has an 'else-clause'.
+                return;
+            }
+
             var containingBlock = GetOperation(
                 semanticModel, ifOperation.Syntax.Parent, cancellationToken) as IBlockStatement;
             if (containingBlock == null)