Detect unused record parameters (#48895)

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -6579,4 +6579,10 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_FunctionPointersCannotBeCalledWithNamedArguments" xml:space="preserve">
     <value>A function pointer cannot be called with named arguments.</value>
   </data>
+  <data name="WRN_UnreadRecordParameter" xml:space="preserve">
+    <value>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</value>
+  </data>
+  <data name="WRN_UnreadRecordParameter_Title" xml:space="preserve">
+    <value>Parameter is unread. Did you forget to use it to initialize the property with that name?</value>
+  </data>
 </root>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -1924,6 +1924,8 @@ internal enum ErrorCode
 
         ERR_EqualityContractRequiresGetter = 8906,
 
+        WRN_UnreadRecordParameter = 8907,
+
         #endregion diagnostics introduced for C# 9.0
 
         // Note: you will need to re-generate compiler code after adding warnings (eng\generate-compiler-code.cmd)

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -470,6 +470,7 @@ internal static int GetWarningLevel(ErrorCode code)
                 case ErrorCode.WRN_ParameterNotNullIfNotNull:
                 case ErrorCode.WRN_ReturnNotNullIfNotNull:
                 case ErrorCode.WRN_AnalyzerReferencesFramework:
+                case ErrorCode.WRN_UnreadRecordParameter:
                     return 1;
                 default:
                     return 0;

src/Compilers/CSharp/Portable/FlowAnalysis/DefiniteAssignment.cs

@@ -49,6 +49,13 @@ internal partial class DefiniteAssignmentPass : LocalDataFlowPass<
         /// </summary>
         private readonly PooledHashSet<LocalSymbol> _usedVariables = PooledHashSet<LocalSymbol>.GetInstance();
 
+#nullable enable
+        /// <summary>
+        /// Parameters of record primary constructors that were read anywhere.
+        /// </summary>
+        private PooledHashSet<ParameterSymbol>? _readParameters;
+#nullable disable
+
         /// <summary>
         /// Variables that were used anywhere, in the sense required to suppress warnings about
         /// unused variables.
@@ -186,6 +193,7 @@ internal partial class DefiniteAssignmentPass : LocalDataFlowPass<
         protected override void Free()
         {
             _usedVariables.Free();
+            _readParameters?.Free();
             _usedLocalFunctions.Free();
             _writtenVariables.Free();
             _capturedVariables.Free();
@@ -506,6 +514,17 @@ protected void Analyze(ref bool badRegion, DiagnosticBag diagnostics)
                 }
 
                 diagnostics.AddRange(this.Diagnostics);
+
+                if (CurrentSymbol is SynthesizedRecordConstructor)
+                {
+                    foreach (ParameterSymbol parameter in MethodParameters)
+                    {
+                        if (_readParameters?.Contains(parameter) != true)
+                        {
+                            diagnostics.Add(ErrorCode.WRN_UnreadRecordParameter, parameter.Locations.FirstOrNone(), parameter.Name);
+                        }
+                    }
+                }
             }
         }
 
@@ -550,6 +569,14 @@ private void NoteCaptured(Symbol variable)
 
         #region Tracking reads/writes of variables for warnings
 
+        private void NoteRecordParameterReadIfNeeded(Symbol symbol)
+        {
+            if (symbol is ParameterSymbol { ContainingSymbol: SynthesizedRecordConstructor } parameter)
+            {
+                _readParameters ??= PooledHashSet<ParameterSymbol>.GetInstance();
+                _readParameters.Add(parameter);
+            }
+        }
         protected virtual void NoteRead(
             Symbol variable,
             ParameterSymbol rangeVariableUnderlyingParameter = null)
@@ -560,6 +587,8 @@ private void NoteCaptured(Symbol variable)
                 _usedVariables.Add(local);
             }
 
+            NoteRecordParameterReadIfNeeded(variable);
+
             var localFunction = variable as LocalFunctionSymbol;
             if ((object)localFunction != null)
             {
@@ -1878,6 +1907,10 @@ public override BoundNode VisitParameter(BoundParameter node)
             {
                 CheckAssigned(node.ParameterSymbol, node.Syntax);
             }
+            else
+            {
+                NoteRecordParameterReadIfNeeded(node.ParameterSymbol);
+            }
 
             return null;
         }

src/Compilers/CSharp/Portable/Generated/ErrorFacts.Generated.cs

@@ -266,6 +266,7 @@ public static bool IsWarning(ErrorCode code)
                 case ErrorCode.WRN_SyncAndAsyncEntryPoints:
                 case ErrorCode.WRN_ParameterIsStaticClass:
                 case ErrorCode.WRN_ReturnTypeIsStaticClass:
+                case ErrorCode.WRN_UnreadRecordParameter:
                     return true;
                 default:
                     return false;

src/Compilers/CSharp/Portable/xlf/CSharpResources.cs.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Není inicializované pole, které nemůže mít hodnotu null. Zvažte možnost deklarovat ho jako typ s možnou hodnotou null.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.de.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Das Non-Nullable-Feld ist nicht initialisiert. Deklarieren Sie das Feld ggf. als "Nullable".</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.es.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">El campo que acepta valores NULL está sin inicializar. Considere la posibilidad de declararlo como que acepta valores NULL.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.fr.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Le champ non-nullable n'est pas initialisé. Déclarez-le comme étant nullable.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.it.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Il campo che non ammette i valori Null non è inizializzato. Provare a dichiararlo in modo che ammetta i valori Null.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.ja.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Null 非許容フィールドは初期化されていません。null 許容として宣言することを検討してください。</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.ko.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">null을 허용하지 않는 필드가 초기화되지 않았습니다. nullable로 선언하는 것이 좋습니다.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.pl.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Nienullowalne pole jest niezainicjowane. Rozważ zadeklarowanie go jako nullowalnego.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.pt-BR.xlf

@@ -2879,6 +2879,16 @@
         <target state="needs-review-translation">O campo não anulável não foi inicializado. Considere declará-lo como anulável.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.ru.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Поле, не допускающее значение NULL, не инициализировано. Рекомендуется объявить его как допускающее значение NULL.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.tr.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">Null değer atanamayan alan başlatılmadı. Bunu null değer atanabilir olarak tanımlamayı deneyin.</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.zh-Hans.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">不可为 null 的字段未初始化。请考虑声明为可以为 null。</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Portable/xlf/CSharpResources.zh-Hant.xlf

@@ -2881,6 +2881,16 @@
         <target state="needs-review-translation">不可為 null 的欄位未初始化。請考慮宣告為可為 null。</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter">
+        <source>Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter '{0}' is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_UnreadRecordParameter_Title">
+        <source>Parameter is unread. Did you forget to use it to initialize the property with that name?</source>
+        <target state="new">Parameter is unread. Did you forget to use it to initialize the property with that name?</target>
+        <note />
+      </trans-unit>
       <trans-unit id="WRN_UseDefViolation">
         <source>Use of unassigned local variable '{0}'</source>
         <target state="new">Use of unassigned local variable '{0}'</target>

src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

@@ -68086,7 +68086,7 @@ record Rec2<T>(T t = default)
    T t { get; } = t; // 2
 }
 
-record Rec3<T>(T t = default)
+record Rec3<T>(T t = default) // 3
 {
    T t { get; } = default!;
 }
@@ -68098,7 +68098,10 @@ record Rec3<T>(T t = default)
                 Diagnostic(ErrorCode.WRN_NullReferenceAssignment, "T t = default").WithLocation(2, 16),
                 // (8,19): warning CS8601: Possible null reference assignment.
                 //    T t { get; } = t; // 2
-                Diagnostic(ErrorCode.WRN_NullReferenceAssignment, "t").WithLocation(8, 19)
+                Diagnostic(ErrorCode.WRN_NullReferenceAssignment, "t").WithLocation(8, 19),
+                // (11,18): warning CS8907: Parameter 't' is unread. Did you forget to use it to initialize the property with that name?
+                // record Rec3<T>(T t = default) // 3
+                Diagnostic(ErrorCode.WRN_UnreadRecordParameter, "t").WithArguments("t").WithLocation(11, 18)
                 );
         }
 

src/Compilers/CSharp/Test/Syntax/Diagnostics/DiagnosticTest.cs

@@ -261,6 +261,7 @@ public void WarningLevel_2()
                         case ErrorCode.WRN_RecordNamedDisallowed:
                         case ErrorCode.WRN_ParameterNotNullIfNotNull:
                         case ErrorCode.WRN_ReturnNotNullIfNotNull:
+                        case ErrorCode.WRN_UnreadRecordParameter:
                             Assert.Equal(1, ErrorFacts.GetWarningLevel(errorCode));
                             break;
                         case ErrorCode.WRN_MainIgnored:
@@ -415,6 +416,7 @@ public void NullableWarnings()
                     ErrorCode.WRN_RecordNamedDisallowed,
                     ErrorCode.WRN_RecordEqualsWithoutGetHashCode,
                     ErrorCode.WRN_AnalyzerReferencesFramework,
+                    ErrorCode.WRN_UnreadRecordParameter,
                 };
 
                 Assert.Contains(error, nullableUnrelatedWarnings);