Fix IDE0031 false positive when preprocessor directives are used in if statements

src/Analyzers/CSharp/Analyzers/UseNullPropagation/CSharpUseNullPropagationDiagnosticAnalyzer.cs

@@ -4,6 +4,7 @@
 
 using System.Collections.Immutable;
 using System.Diagnostics.CodeAnalysis;
+using System.Threading;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
@@ -102,4 +103,16 @@ protected override bool TryGetPartsOfIfStatement(
 
         return true;
     }
+
+    public override IfStatementAnalysisResult? AnalyzeIfStatement(
+        SemanticModel semanticModel,
+        IMethodSymbol? referenceEqualsMethod,
+        IfStatementSyntax ifStatement,
+        CancellationToken cancellationToken)
+    {
+        if (ifStatement.Statement.ContainsDirectives)
+            return null;
+
+        return base.AnalyzeIfStatement(semanticModel, referenceEqualsMethod, ifStatement, cancellationToken);
+    }
 }

src/Analyzers/CSharp/Tests/UseNullPropagation/UseNullPropagationTests.cs

@@ -2779,4 +2779,138 @@ public bool Equals(Element<T> x)
             }
             """,
             languageVersion: LanguageVersion.CSharp14);
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/65880")]
+    public Task TestIfStatement_WithPreprocessorDirectiveInBlock()
+        => TestMissingInRegularAndScriptAsync(
+            """
+            #nullable enable
+            using System.Diagnostics;
+
+            class C
+            {
+                private object? _controlToLayout;
+                private bool _resumeLayout;
+                private int _layoutSuspendCount;
+
+                public void Dispose()
+                {
+                    if (_controlToLayout is not null)
+                    {
+                        _controlToLayout.ToString();
+
+            #if DEBUG
+                        Debug.Assert(_layoutSuspendCount == 0, "Suspend/Resume layout mismatch!");
+            #endif
+                    }
+                }
+            }
+            """);
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/65880")]
+    public Task TestIfStatement_WithPreprocessorDirective_DEBUG()
+        => TestMissingInRegularAndScriptAsync(
+            """
+            #nullable enable
+            using System.Diagnostics;
+
+            class C
+            {
+                private object? _controlToLayout;
+
+                public void Dispose()
+                {
+                    if (_controlToLayout != null)
+                    {
+                        _controlToLayout.ToString();
+
+            #if DEBUG
+                        Debug.WriteLine("Debug mode");
+            #endif
+                    }
+                }
+            }
+            """);
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/65880")]
+    public Task TestIfStatement_WithPreprocessorDirective_BeforeStatement()
+        => TestMissingInRegularAndScriptAsync(
+            """
+            #nullable enable
+            using System.Diagnostics;
+
+            class C
+            {
+                private object? _controlToLayout;
+
+                public void Dispose()
+                {
+                    if (_controlToLayout != null)
+                    {
+            #if DEBUG
+                        Debug.WriteLine("Debug mode");
+            #endif
+                        _controlToLayout.ToString();
+                    }
+                }
+            }
+            """);
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/65880")]
+    public Task TestIfStatement_WithoutPreprocessorDirective_StillWorks()
+        => TestInRegularAndScriptAsync(
+            """
+            #nullable enable
+            using System;
+
+            class C
+            {
+                private object? _controlToLayout;
+
+                public void Dispose()
+                {
+                    [|if|] (_controlToLayout != null)
+                    {
+                        _controlToLayout.ToString();
+                    }
+                }
+            }
+            """,
+            """
+            #nullable enable
+            using System;
+
+            class C
+            {
+                private object? _controlToLayout;
+
+                public void Dispose()
+                {
+                    _controlToLayout?.ToString();
+                }
+            }
+            """);
+
+    [Fact, WorkItem("https://github.com/dotnet/roslyn/issues/65880")]
+    public Task TestIfStatement_SingleStatement_WithPreprocessorDirective()
+        => TestMissingInRegularAndScriptAsync(
+            """
+            #nullable enable
+            using System.Diagnostics;
+
+            class C
+            {
+                private object? _controlToLayout;
+
+                public void Dispose()
+                {
+                    if (_controlToLayout != null)
+            #if DEBUG
+                        _controlToLayout.ToString();
+            #else
+                        Debug.WriteLine("null");
+            #endif
+                }
+            }
+            """);
 }

src/Analyzers/Core/Analyzers/UseNullPropagation/AbstractUseNullPropagationDiagnosticAnalyzer_IfStatement.cs

@@ -54,7 +54,7 @@ private void AnalyzeIfStatementAndReportDiagnostic(
 
     }
 
-    public IfStatementAnalysisResult? AnalyzeIfStatement(
+    public virtual IfStatementAnalysisResult? AnalyzeIfStatement(
         SemanticModel semanticModel,
         IMethodSymbol? referenceEqualsMethod,
         TIfStatementSyntax ifStatement,