Parameter Shadowing Error Fix (#26924)

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

@@ -14515,6 +14515,24 @@ internal class CSharpResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Type parameter &apos;{0}&apos; has the same name as the type parameter from outer method &apos;{1}&apos;.
+        /// </summary>
+        internal static string WRN_TypeParameterSameAsOuterMethodTypeParameter {
+            get {
+                return ResourceManager.GetString("WRN_TypeParameterSameAsOuterMethodTypeParameter", resourceCulture);
+            }
+        }
+        
+        /// <summary>
+        ///   Looks up a localized string similar to Type parameter has the same type as the type parameter from outer method..
+        /// </summary>
+        internal static string WRN_TypeParameterSameAsOuterMethodTypeParameter_Title {
+            get {
+                return ResourceManager.GetString("WRN_TypeParameterSameAsOuterMethodTypeParameter_Title", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Type parameter &apos;{0}&apos; has the same name as the type parameter from outer type &apos;{1}&apos;.
         /// </summary>

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -1943,6 +1943,12 @@ If such a class is used as a base class and if the deriving class defines a dest
   <data name="WRN_TypeParameterSameAsOuterTypeParameter_Title" xml:space="preserve">
     <value>Type parameter has the same name as the type parameter from outer type</value>
   </data>
+  <data name="WRN_TypeParameterSameAsOuterMethodTypeParameter" xml:space="preserve">
+    <value>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</value>
+  </data>
+  <data name="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title" xml:space="preserve">
+    <value>Type parameter has the same type as the type parameter from outer method.</value>
+  </data>
   <data name="ERR_TypeVariableSameAsParent" xml:space="preserve">
     <value>Type parameter '{0}' has the same name as the containing type, or method</value>
   </data>
@@ -5333,4 +5339,4 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_OutVariableCannotBeByRef" xml:space="preserve">
     <value>An out variable cannot be declared as a ref local</value>
   </data>
-</root>
\ No newline at end of file
+</root>

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

@@ -1527,7 +1527,6 @@ internal enum ErrorCode
         ERR_RefStructInterfaceImpl = 8343,
         ERR_BadSpecialByRefIterator = 8344,
         ERR_FieldAutoPropCantBeByRefLike = 8345,
-
         ERR_StackAllocConversionNotPossible = 8346,
 
         ERR_EscapeCall = 8347,
@@ -1577,8 +1576,8 @@ internal enum ErrorCode
         ERR_ExprCannotBeFixed = 8385,
         ERR_InvalidObjectCreation = 8386,
         #endregion diagnostics introduced for C# 7.3
-
-        ERR_OutVariableCannotBeByRef = 8387,
+        WRN_TypeParameterSameAsOuterMethodTypeParameter = 8387,
+        ERR_OutVariableCannotBeByRef = 8388,
     }
     // Note: you will need to re-generate compiler code after adding warnings (build\scripts\generate-compiler-code.cmd)
 }

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

@@ -323,6 +323,7 @@ internal static int GetWarningLevel(ErrorCode code)
                 case ErrorCode.WRN_Experimental:
                 case ErrorCode.WRN_AttributesOnBackingFieldsNotAvailable:
                 case ErrorCode.WRN_TupleBinopLiteralNameMismatch:
+                case ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter:
                     return 1;
                 default:
                     return 0;

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

@@ -179,6 +179,7 @@ public static bool IsWarning(ErrorCode code)
                 case ErrorCode.WRN_FilterIsConstantFalseRedundantTryCatch:
                 case ErrorCode.WRN_AttributesOnBackingFieldsNotAvailable:
                 case ErrorCode.WRN_TupleBinopLiteralNameMismatch:
+                case ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter:
                     return true;
                 default:
                     return false;

src/Compilers/CSharp/Portable/Symbols/Source/LocalFunctionSymbol.cs

@@ -402,8 +402,19 @@ private ImmutableArray<SourceMethodTypeParameterSymbol> MakeTypeParameters(Diagn
                 var tpEnclosing = ContainingSymbol.FindEnclosingTypeParameter(name);
                 if ((object)tpEnclosing != null)
                 {
-                    // Type parameter '{0}' has the same name as the type parameter from outer type '{1}'
-                    diagnostics.Add(ErrorCode.WRN_TypeParameterSameAsOuterTypeParameter, location, name, tpEnclosing.ContainingSymbol);
+                    ErrorCode typeError;
+                    if (tpEnclosing.ContainingSymbol.Kind == SymbolKind.Method)
+                    {
+                        // Type parameter '{0}' has the same name as the type parameter from outer method '{1}'
+                        typeError = ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter;
+                    }
+                    else
+                    {
+                        Debug.Assert(tpEnclosing.ContainingSymbol.Kind == SymbolKind.NamedType);
+                        // Type parameter '{0}' has the same name as the type parameter from outer type '{1}'
+                        typeError = ErrorCode.WRN_TypeParameterSameAsOuterTypeParameter;
+                    }
+                    diagnostics.Add(typeError, location, name, tpEnclosing.ContainingSymbol);
                 }
 
                 var typeParameter = new SourceMethodTypeParameterSymbol(

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">Znaky {0} se na tomto místě nedají použít.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">Zeichen "{0}" können an dieser Stelle nicht verwendet werden.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">El/los carácter/caracteres '{0}' no se puede/n usar en esta ubicación.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">Impossible d'utiliser le(s) caractère(s) '{0}' à cet emplacement.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">Non è possibile usare il carattere o i caratteri '{0}' in questa posizione.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">文字 '{0}' はこの位置では使用できません。</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">{0}' 문자를 이 위치에 사용할 수 없습니다.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">Znaków „{0}” nie można użyć w tej lokalizacji.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">O(s) caractere(s) "{0}" não pode(m) ser usado(s) neste local.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">В этом месте нельзя использовать символы "{0}".</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">{0}' karakterleri bu konumda kullanılamaz.</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">此位置无法使用字符“{0}”。</target>

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

@@ -387,6 +387,16 @@
         <target state="new">SyntaxTree is not part of the compilation, so it cannot be removed</target>
         <note />
       </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter">
+        <source>Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</source>
+        <target state="new">Type parameter '{0}' has the same name as the type parameter from outer method '{1}'</target>
+        <note />
+      </trans-unit>
+      <trans-unit id="WRN_TypeParameterSameAsOuterMethodTypeParameter_Title">
+        <source>Type parameter has the same type as the type parameter from outer method.</source>
+        <target state="new">Type parameter has the same type as the type parameter from outer method.</target>
+        <note />
+      </trans-unit>
       <trans-unit id="XML_InvalidToken">
         <source>The character(s) '{0}' cannot be used at this location.</source>
         <target state="translated">此位置不可使用字元 '{0}'。</target>

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

-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+// 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 Microsoft.CodeAnalysis.CSharp.Symbols;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -1064,12 +1064,12 @@ int Local2<U>()
                 // (18,26): error CS0692: Duplicate type parameter 'T'
                 //             int Local<T, T>() => 0;
                 Diagnostic(ErrorCode.ERR_DuplicateTypeParameter, "T").WithArguments("T").WithLocation(18, 26),
-                // (25,23): warning CS0693: Type parameter 'T' has the same name as the type parameter from outer type 'C.M2<T>()'
+                // (25,23): warning CS8387: Type parameter 'T' has the same name as the type parameter from outer method 'C.M2<T>()'
                 //             int Local<T>() => 0;
-                Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterTypeParameter, "T").WithArguments("T", "C.M2<T>()").WithLocation(25, 23),
-                // (31,28): warning CS0693: Type parameter 'V' has the same name as the type parameter from outer type 'Local1<V>()'
+                Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter, "T").WithArguments("T", "C.M2<T>()").WithLocation(25, 23),
+                // (31,28): warning CS8387: Type parameter 'V' has the same name as the type parameter from outer method 'Local1<V>()'
                 //                 int Local2<V>() => 0;
-                Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterTypeParameter, "V").WithArguments("V", "Local1<V>()").WithLocation(31, 28),
+                Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter, "V").WithArguments("V", "Local1<V>()").WithLocation(31, 28),
                 // (37,17): error CS0412: 'T': a parameter, local variable, or local function cannot have the same name as a method type parameter
                 //             int T() => 0;
                 Diagnostic(ErrorCode.ERR_LocalSameNameAsTypeParam, "T").WithArguments("T").WithLocation(37, 17),
@@ -1079,9 +1079,9 @@ int Local2<U>()
                 // (54,25): error CS0412: 'T': a parameter, local variable, or local function cannot have the same name as a method type parameter
                 //                     int T() => 0;
                 Diagnostic(ErrorCode.ERR_LocalSameNameAsTypeParam, "T").WithArguments("T").WithLocation(54, 25),
-                // (67,32): warning CS0693: Type parameter 'T' has the same name as the type parameter from outer type 'C.M2<T>()'
+                // (67,32): warning CS8387: Type parameter 'T' has the same name as the type parameter from outer method 'C.M2<T>()'
                 //                     int Local3<T>() => 0;
-                Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterTypeParameter, "T").WithArguments("T", "C.M2<T>()").WithLocation(67, 32));
+                Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter, "T").WithArguments("T", "C.M2<T>()").WithLocation(67, 32));
         }
 
         [Fact]
@@ -1803,9 +1803,9 @@ T Inner<T>()
 }
 ";
             VerifyDiagnostics(source,
-    // (8,21): warning CS0693: Type parameter 'T' has the same name as the type parameter from outer type 'Outer<T>()'
+    // (8,21): warning CS8387: Type parameter 'T' has the same name as the type parameter from outer method 'Outer<T>()'
     //             T Inner<T>()
-    Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterTypeParameter, "T").WithArguments("T", "Outer<T>()").WithLocation(8, 21)
+    Diagnostic(ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter, "T").WithArguments("T", "Outer<T>()").WithLocation(8, 21)
     );
         }
 

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

@@ -244,6 +244,7 @@ public void WarningLevel_2()
                         case ErrorCode.WRN_Experimental:
                         case ErrorCode.WRN_AttributesOnBackingFieldsNotAvailable:
                         case ErrorCode.WRN_TupleBinopLiteralNameMismatch:
+                        case ErrorCode.WRN_TypeParameterSameAsOuterMethodTypeParameter:
                             Assert.Equal(1, ErrorFacts.GetWarningLevel(errorCode));
                             break;
                         case ErrorCode.WRN_MainIgnored: