Do not suggest pattern matching in expression tree (fix #901) (RCS1248)

Author: josefpihrt

src/Analyzers/CSharp/Analysis/NormalizeNullCheckAnalyzer.cs

@@ -70,14 +70,13 @@ private static void AnalyzeEqualsExpression(SyntaxNodeAnalysisContext context)
 
             NullCheckExpressionInfo nullCheck = SyntaxInfo.NullCheckExpressionInfo(binaryExpression, allowedStyles: NullCheckStyles.EqualsToNull, walkDownParentheses: false);
 
-            if (nullCheck.Success)
-            {
-                DiagnosticHelpers.ReportDiagnostic(
-                    context,
-                    DiagnosticRules.NormalizeNullCheck,
-                    binaryExpression,
-                    "pattern matching");
-            }
+            if (!nullCheck.Success)
+                return;
+
+            if (binaryExpression.IsInExpressionTree(context.SemanticModel, context.CancellationToken))
+                return;
+
+            ReportDiagnostic(context, binaryExpression, "pattern matching");
         }
 
         private static void AnalyzeNotEqualsExpression(SyntaxNodeAnalysisContext context)
@@ -89,14 +88,13 @@ private static void AnalyzeNotEqualsExpression(SyntaxNodeAnalysisContext context
 
             NullCheckExpressionInfo nullCheck = SyntaxInfo.NullCheckExpressionInfo(binaryExpression, allowedStyles: NullCheckStyles.NotEqualsToNull);
 
-            if (nullCheck.Success)
-            {
-                DiagnosticHelpers.ReportDiagnostic(
-                    context,
-                    DiagnosticRules.NormalizeNullCheck,
-                    binaryExpression,
-                    "pattern matching");
-            }
+            if (!nullCheck.Success)
+                return;
+
+            if (binaryExpression.IsInExpressionTree(context.SemanticModel, context.CancellationToken))
+                return;
+
+            ReportDiagnostic(context, binaryExpression, "pattern matching");
         }
 
         private static void AnalyzeIsPatternExpression(SyntaxNodeAnalysisContext context)
@@ -109,12 +107,17 @@ private static void AnalyzeIsPatternExpression(SyntaxNodeAnalysisContext context
             if (isPatternExpression.Pattern is ConstantPatternSyntax constantPattern
                 && constantPattern.Expression.IsKind(SyntaxKind.NullLiteralExpression))
             {
-                DiagnosticHelpers.ReportDiagnostic(
-                    context,
-                    DiagnosticRules.NormalizeNullCheck,
-                    isPatternExpression,
-                    "equality operator");
+                ReportDiagnostic(context, isPatternExpression, "equality operator");
             }
         }
+
+        private static void ReportDiagnostic(SyntaxNodeAnalysisContext context, ExpressionSyntax expression, string messageArg)
+        {
+            DiagnosticHelpers.ReportDiagnostic(
+                context,
+                DiagnosticRules.NormalizeNullCheck,
+                expression,
+                messageArg);
+        }
     }
 }

src/Tests/Analyzers.Tests/RCS1248NormalizeNullCheckTests.cs

@@ -184,5 +184,32 @@ void M()
 ", options: WellKnownCSharpTestOptions.Default_CSharp8
                 .AddConfigOption(ConfigOptionKeys.NullCheckStyle, ConfigOptionValues.NullCheckStyle_PatternMatching));
         }
+
+        [Fact, Trait(Traits.Analyzer, DiagnosticIdentifiers.NormalizeNullCheck)]
+        public async Task TestNoDiagnostic_ExpressionTree()
+        {
+            await VerifyNoDiagnosticAsync(@"
+using System.Collections.Generic;
+using System.Linq;
+
+class C
+{
+    void M()
+    {
+        var items = default(IQueryable<C>);
+
+        var items2 = items
+            .Where(f => f.P == null)
+            .ToList();
+
+        var items3 = items
+            .Where(f => f.P != null)
+            .ToList();
+    }
+
+    public object P { get; }
+}
+", options: Options.AddConfigOption(ConfigOptionKeys.NullCheckStyle, ConfigOptionValues.NullCheckStyle_PatternMatching));
+        }
     }
 }