Fix analyzer RCS1248 (#1677)

Author: josefpihrt

ChangeLog.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fix analyzer [RCS1246](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1246) ([PR](https://github.com/dotnet/roslynator/pull/1676))
+- Fix analyzer [RCS1248](https://josefpihrt.github.io/docs/roslynator/analyzers/RCS1248) ([PR](https://github.com/dotnet/roslynator/pull/1677))
 
 ## [4.14.0] - 2025-07-26
 

src/CSharp/CSharp/Extensions/SyntaxExtensions.cs

@@ -2918,6 +2918,15 @@ public static bool IsInExpressionTree(
                 case SyntaxKind.GroupClause:
                 case SyntaxKind.SelectClause:
                 {
+                    if (semanticModel
+                        .GetTypeInfo(current, cancellationToken)
+                        .ConvertedType?
+                        .OriginalDefinition
+                        .HasMetadataName(MetadataNames.System_Linq_IQueryable_T) == true)
+                    {
+                        return true;
+                    }
+
                     SymbolInfo symbolInfo = semanticModel.GetSymbolInfo(current, cancellationToken);
 
                     if (IsMethodThatAcceptsExpressionAsFirstParameter(symbolInfo))

src/Tests/Analyzers.Tests/RCS1248NormalizeNullCheckTests.cs

@@ -209,6 +209,29 @@ void M()
 
     public object P { get; }
 }
+", options: Options.AddConfigOption(ConfigOptionKeys.NullCheckStyle, ConfigOptionValues.NullCheckStyle_PatternMatching));
+    }
+
+    [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.NormalizeNullCheck)]
+    public async Task TestNoDiagnostic_ExpressionTree2()
+    {
+        await VerifyNoDiagnosticAsync(@"
+using System.Linq;
+
+class C
+{
+    void M()
+    {
+        var _ = from x in new[] { ""a"" }.AsQueryable()
+                join yy in new[] { ""b"" }.AsQueryable()
+                on x equals yy into y
+                from yy in y.DefaultIfEmpty()
+                select new
+                {
+                    A = yy != null
+                };
+    }
+}
 ", options: Options.AddConfigOption(ConfigOptionKeys.NullCheckStyle, ConfigOptionValues.NullCheckStyle_PatternMatching));
     }
 }