Update Coalesce-for-nullables as well.

src/EditorFeatures/CSharpTest/UseCoalesceExpression/UseCoalesceExpressionForNullableTests.cs

@@ -184,6 +184,33 @@ void M(int? x, int? y, int? z)
     {
         var w = x ?? y ?? z;
     }
+}");
+        }
+
+        [WorkItem(17028, "https://github.com/dotnet/roslyn/issues/17028")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseCoalesceExpression)]
+        public async Task TestInExpressionOfT()
+        {
+            await TestAsync(
+@"using System;
+using System.Linq.Expressions;
+
+class C
+{
+    void M(int? x, int? y)
+    {
+        Expression<Func<int>> e = () => [||]!x.HasValue ? y : x.Value;
+    }
+}",
+@"using System;
+using System.Linq.Expressions;
+
+class C
+{
+    void M(int? x, int? y)
+    {
+        Expression<Func<int>> e = () => {|Warning:x ?? y|};
+    }
 }");
         }
     }

src/EditorFeatures/VisualBasicTest/UseCoalesceExpression/UseCoalesceExpressionTests.vb

@@ -247,7 +247,7 @@ Imports System.Linq.Expressions
 
 Class C
     Sub M(x as string, y as string)
-        dim e as Expression(of Func(of string)) = [||]If (x isnot Nothing, x, y)
+        dim e as Expression(of Func(of string)) = func() [||]If (x isnot Nothing, x, y)
     End Sub
 End Class",
 "Imports System
@@ -255,7 +255,7 @@ Imports System.Linq.Expressions
 
 Class C
     Sub M(x as string, y as string, z as string)
-        dim e as Expression(of Func(of string)) = If (x, y)
+        dim e as Expression(of Func(of string)) = func () If (x, y)
     End Sub
 End Class")
         End Function

src/Features/Core/Portable/UseCoalesceExpression/UseCoalesceExpressionForNullableCodeFixProvider.cs

@@ -33,11 +33,15 @@ public override Task RegisterCodeFixesAsync(CodeFixContext context)
             return SpecializedTasks.EmptyTask;
         }
 
-        protected override Task FixAllAsync(
+        protected override async Task FixAllAsync(
             Document document, ImmutableArray<Diagnostic> diagnostics,
             SyntaxEditor editor, CancellationToken cancellationToken)
         {
+            var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            var expressionTypeOpt = semanticModel.Compilation.GetTypeByMetadataName("System.Linq.Expressions.Expression`1");
+
             var syntaxFacts = document.GetLanguageService<ISyntaxFactsService>();
+            var semanticFacts = document.GetLanguageService<ISemanticFactsService>();
             var generator = editor.Generator;
             var root = editor.OriginalRoot;
 
@@ -54,13 +58,20 @@ public override Task RegisterCodeFixesAsync(CodeFixContext context)
                         syntaxFacts.GetPartsOfConditionalExpression(
                             c, out var currentCondition, out var currentWhenTrue, out var currentWhenFalse);
 
-                        return whenPart == whenTrue
+                        var coalesceExpression = whenPart == whenTrue
                             ? g.CoalesceExpression(conditionExpression, syntaxFacts.WalkDownParentheses(currentWhenTrue))
                             : g.CoalesceExpression(conditionExpression, syntaxFacts.WalkDownParentheses(currentWhenFalse));
+
+                        if (semanticFacts.IsInExpressionTree(
+                                semanticModel, conditionalExpression, expressionTypeOpt, cancellationToken))
+                        {
+                            coalesceExpression = coalesceExpression.WithAdditionalAnnotations(
+                                WarningAnnotation.Create(FeaturesResources.Changes_to_expression_trees_may_result_in_behavior_changes_at_runtime));
+                        }
+
+                        return coalesceExpression;
                     });
             }
-
-            return SpecializedTasks.EmptyTask;
         }
 
         private class MyCodeAction : CodeAction.DocumentChangeAction