CA2246 Warning for unobvious assignment

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/MicrosoftQualityGuidelinesAnalyzersResources.resx

@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
 <root>
-  <!--
-    Microsoft ResX Schema
-
+  <!-- 
+    Microsoft ResX Schema 
+    
     Version 2.0
-
-    The primary goals of this format is to allow a simple XML format
-    that is mostly human readable. The generation and parsing of the
-    various data types are done through the TypeConverter classes
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
     associated with the data types.
-
+    
     Example:
-
+    
     ... ado.net/XML headers & schema ...
     <resheader name="resmimetype">text/microsoft-resx</resheader>
     <resheader name="version">2.0</resheader>
@@ -26,36 +26,36 @@
         <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
         <comment>This is a comment</comment>
     </data>
-
-    There are any number of "resheader" rows that contain simple
+                
+    There are any number of "resheader" rows that contain simple 
     name/value pairs.
-
-    Each data row contains a name, and value. The row also contains a
-    type or mimetype. Type corresponds to a .NET class that support
-    text/value conversion through the TypeConverter architecture.
-    Classes that don't support this are serialized and stored with the
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
     mimetype set.
-
-    The mimetype is used for serialized objects, and tells the
-    ResXResourceReader how to depersist the object. This is currently not
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
     extensible. For a given mimetype the value must be set accordingly:
-
-    Note - application/x-microsoft.net.object.binary.base64 is the format
-    that the ResXResourceWriter will generate, however the reader can
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
     read any of the formats listed below.
-
+    
     mimetype: application/x-microsoft.net.object.binary.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
             : and then encoded with base64 encoding.
-
+    
     mimetype: application/x-microsoft.net.object.soap.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
             : and then encoded with base64 encoding.
 
     mimetype: application/x-microsoft.net.object.bytearray.base64
-    value   : The object must be serialized into a byte array
+    value   : The object must be serialized into a byte array 
             : using a System.ComponentModel.TypeConverter
             : and then encoded with base64 encoding.
     -->
@@ -252,4 +252,10 @@
   <data name="AvoidPropertySelfAssignmentMessage" xml:space="preserve">
     <value>The property {0} should not be assigned to itself.</value>
   </data>
+  <data name="ReferingToObjectAndReassigningItInTheSameStatementMessage" xml:space="preserve">
+    <value>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</value>
+  </data>
+  <data name="ReferingToObjectAndReassigningItInTheSameStatementTitle" xml:space="preserve">
+    <value>Refering to object and reassigning it in the same statement.</value>
+  </data>
 </root>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/ReferingToObjectAndReassigningItInTheSameStatement.cs

@@ -0,0 +1,96 @@
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Immutable;
+using Analyzer.Utilities;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+namespace Microsoft.CodeQuality.Analyzers.QualityGuidelines
+{
+    /// <summary>
+    /// ReferenceChanged: Prevent objects from being referenced in statements where they are reassigned
+    /// </summary>
+    [DiagnosticAnalyzer(LanguageNames.CSharp, LanguageNames.VisualBasic)]
+
+    public sealed class ReferingToObjectAndReassigningItInTheSameStatement : DiagnosticAnalyzer
+    {
+        internal const string RuleId = "ReferenceChanged";
+
+        private static readonly LocalizableString s_localizableTitle = new LocalizableResourceString(nameof(MicrosoftQualityGuidelinesAnalyzersResources.ReferingToObjectAndReassigningItInTheSameStatementTitle), MicrosoftQualityGuidelinesAnalyzersResources.ResourceManager, typeof(MicrosoftQualityGuidelinesAnalyzersResources));
+        private static readonly LocalizableString s_localizableMessage = new LocalizableResourceString(nameof(MicrosoftQualityGuidelinesAnalyzersResources.ReferingToObjectAndReassigningItInTheSameStatementMessage), MicrosoftQualityGuidelinesAnalyzersResources.ResourceManager, typeof(MicrosoftQualityGuidelinesAnalyzersResources));
+
+        internal static DiagnosticDescriptor Rule = new DiagnosticDescriptor(RuleId,
+            s_localizableTitle,
+            s_localizableMessage,
+            DiagnosticCategory.Usage,
+            DiagnosticHelpers.DefaultDiagnosticSeverity,
+            isEnabledByDefault: DiagnosticHelpers.EnabledByDefaultIfNotBuildingVSIX,
+            helpLinkUri: null);
+
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.RegisterOperationAction(AnalyzeAssignment, OperationKind.SimpleAssignment);
+        }
+
+        private void AnalyzeAssignment(OperationAnalysisContext context)
+        {
+            var assignmentOperation = (ISimpleAssignmentOperation)context.Operation;
+
+            // Check if there are more then one assignment in a statement
+            if (!(assignmentOperation.Target is IMemberReferenceOperation operationTarget))
+            {
+                return;
+            }
+
+            // This analyzer makes sense only for reference type objects
+            if (operationTarget.Instance?.Type.IsValueType == true)
+            {
+                return;
+            }
+
+            // Search for object equal to operationTarget.Instance further in assignment chain
+            bool isViolationFound = false;
+            string violatingObjectName;
+            if (operationTarget.Instance is ILocalReferenceOperation localInstance)
+            {
+                violatingObjectName = localInstance.Local.Name;
+                isViolationFound = AnalyzeMemberAssignment(assignmentOperation, localInstance, (a, b) => a.Local == b.Local);
+            }
+            else if (operationTarget.Instance is IMemberReferenceOperation memberInstance)
+            {
+                violatingObjectName = memberInstance.Member.Name;
+                isViolationFound = AnalyzeMemberAssignment(assignmentOperation, memberInstance, (a, b) => a.Member == b.Member);
+            }
+            else
+            {
+                return;
+            }
+
+            if (isViolationFound)
+            {
+                var diagnostic = Diagnostic.Create(Rule, operationTarget.Syntax.GetLocation(), violatingObjectName);
+                context.ReportDiagnostic(diagnostic);
+            }
+        }
+
+        private static bool AnalyzeMemberAssignment<T>(ISimpleAssignmentOperation assignmentOperation, T instance, Func<T, T, bool> equalityComparer) where T : class, IOperation
+        {
+            // Check every simple assignments target in a statement for equality to `instance`
+            while (assignmentOperation.Value != null && assignmentOperation.Value.Kind == OperationKind.SimpleAssignment)
+            {
+                assignmentOperation = (ISimpleAssignmentOperation)assignmentOperation.Value;
+
+                var operationValue = assignmentOperation.Target as T;
+                if (equalityComparer(instance, operationValue))
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
+    }
+}

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.cs.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Některé odkazy na {0} nešlo opravit. Měly by se opravit ručně.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Tam, kde je to vhodné, použijte literály</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.de.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Einige Verweise auf "{0}" konnten nicht korrigiert werden. Korrigieren Sie sie manuell.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Nach Möglichkeit Literale verwenden</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.es.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Algunas referencias a "{0}" podrían no corregirse, así que tendría que hacerlo manualmente.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Usar literales cuando resulte apropiado</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.fr.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Des références à '{0}' n'ont pas pu être corrigées, elles doivent être corrigées manuellement.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Utiliser des littéraux quand cela est approprié</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.it.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Non è stato possibile correggere alcuni riferimenti a '{0}'. Correggerli manualmente.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Usa valori letterali dove appropriato</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.ja.xlf

@@ -22,6 +22,16 @@
         <target state="translated">'{0}' への参照を修正できませんでした。手動で修正する必要があります。</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">適切な場所にリテラルを使用します</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.ko.xlf

@@ -22,6 +22,16 @@
         <target state="translated">'{0}'에 대한 일부 참조를 수정할 수 없습니다. 수동으로 수정해야 합니다.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">적합한 리터럴을 사용하세요.</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.pl.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Nie można naprawić niektórych odwołań do „{0}”. Należy je naprawić ręcznie.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Używaj literałów w odpowiednich miejscach</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.pt-BR.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Algumas referências a '{0}' não puderam ser corrigidas, elas devem ser corrigidas manualmente.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Usar literais sempre que apropriado</target>

src/Microsoft.CodeQuality.Analyzers/Core/QualityGuidelines/xlf/MicrosoftQualityGuidelinesAnalyzersResources.ru.xlf

@@ -22,6 +22,16 @@
         <target state="translated">Не удалось исправить некоторые ссылки на "{0}". Их следует исправить вручную.</target>
         <note />
       </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementMessage">
+        <source>Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</source>
+        <target state="new">Object '{0}' is being referred to and reassigned in the same statement. You are at risk of referring to unintended object.</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="ReferingToObjectAndReassigningItInTheSameStatementTitle">
+        <source>Refering to object and reassigning it in the same statement.</source>
+        <target state="new">Refering to object and reassigning it in the same statement.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="UseLiteralsWhereAppropriateTitle">
         <source>Use literals where appropriate</source>
         <target state="translated">Используйте литералы, когда это уместно</target>