Handle possible null symbols in getAttributeTarget

src/Compilers/CSharp/Portable/Compilation/SyntaxTreeSemanticModel.cs

@@ -1289,14 +1289,14 @@ Symbol getAttributeTarget(SyntaxNode targetSyntax)
             {
                 return targetSyntax switch
                 {
-                    BaseMethodDeclarationSyntax methodDeclaration => GetDeclaredMemberSymbol(methodDeclaration),
-                    LocalFunctionStatementSyntax localFunction => GetMemberModel(localFunction)?.GetDeclaredLocalFunction(localFunction),
-                    ParameterSyntax parameterSyntax => ((Symbols.PublicModel.ParameterSymbol)GetDeclaredSymbol(parameterSyntax)).UnderlyingSymbol,
-                    TypeParameterSyntax typeParameterSyntax => ((Symbols.PublicModel.TypeParameterSymbol)GetDeclaredSymbol(typeParameterSyntax)).UnderlyingSymbol,
-                    IndexerDeclarationSyntax indexerSyntax => ((Symbols.PublicModel.PropertySymbol)GetDeclaredSymbol(indexerSyntax)).UnderlyingSymbol,
-                    AccessorDeclarationSyntax accessorSyntax => ((Symbols.PublicModel.MethodSymbol)GetDeclaredSymbol(accessorSyntax)).UnderlyingSymbol,
-                    AnonymousFunctionExpressionSyntax anonymousFunction => ((Symbols.PublicModel.Symbol)GetSymbolInfo(anonymousFunction).Symbol).UnderlyingSymbol,
-                    DelegateDeclarationSyntax delegateSyntax => ((Symbols.PublicModel.NamedTypeSymbol)GetDeclaredSymbol(delegateSyntax)).UnderlyingSymbol,
+                    BaseMethodDeclarationSyntax or
+                        LocalFunctionStatementSyntax or
+                        ParameterSyntax or
+                        TypeParameterSyntax or
+                        IndexerDeclarationSyntax or
+                        AccessorDeclarationSyntax or
+                        DelegateDeclarationSyntax => GetDeclaredSymbolForNode(targetSyntax).GetSymbol(),
+                    AnonymousFunctionExpressionSyntax anonymousFunction => GetSymbolInfo(anonymousFunction).Symbol.GetSymbol(),
                     _ => null
                 };
             }

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

@@ -9748,6 +9748,40 @@ public MyAttribute(string name1) { }
                 );
         }
 
+        [Fact, WorkItem(1556927, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1556927")]
+        public void ParameterScope_ValueLocalNotInPropertyOrAccessorAttributeNameOf_UnknownAccessor()
+        {
+            var source = @"
+class C
+{
+    int Property4 { [My(nameof(value))] unknown => throw null; }
+}
+
+public class MyAttribute : System.Attribute
+{
+    public MyAttribute(string name) { }
+}
+";
+            var comp = CreateCompilation(new[] { source, IsExternalInitTypeDefinition });
+            comp.VerifyDiagnostics(
+                // (4,9): error CS0548: 'C.Property4': property or indexer must have at least one accessor
+                //     int Property4 { [My(nameof(value))] unknown => throw null; }
+                Diagnostic(ErrorCode.ERR_PropertyWithNoAccessors, "Property4").WithArguments("C.Property4").WithLocation(4, 9),
+                // (4,41): error CS1014: A get or set accessor expected
+                //     int Property4 { [My(nameof(value))] unknown => throw null; }
+                Diagnostic(ErrorCode.ERR_GetOrSetExpected, "unknown").WithLocation(4, 41)
+                );
+
+            var tree = comp.SyntaxTrees.First();
+            var model = comp.GetSemanticModel(tree);
+            var node = tree.GetRoot().DescendantNodes().OfType<IdentifierNameSyntax>()
+                .Where(i => i.Identifier.ValueText == "value")
+                .Where(i => i.Ancestors().Any(a => a.IsKind(SyntaxKind.Attribute)))
+                .Single();
+
+            Assert.Null(model.GetSymbolInfo(node).Symbol);
+        }
+
         [Fact]
         public void ParameterScope_InParameterAttributeNameOf_Constructor()
         {
@@ -10429,5 +10463,32 @@ public MyAttribute(string name1) { }
 ");
             comp.VerifyDiagnostics();
         }
+
+        [Fact, WorkItem(1556927, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1556927")]
+        public void LambdaOutsideMemberModel()
+        {
+            var text = @"
+public class MyAttribute : System.Attribute
+{
+    public MyAttribute(string name1) { }
+}
+
+int P
+{
+    badAccessorName
+    {
+        M([My(nameof(P))] env => env);
+";
+            var comp = CreateCompilation(text);
+
+            var tree = comp.SyntaxTrees.First();
+            var model = comp.GetSemanticModel(tree);
+            var node = tree.GetRoot().DescendantNodes().OfType<IdentifierNameSyntax>()
+                .Where(i => i.Identifier.ValueText == "P")
+                .Where(i => i.Ancestors().Any(a => a.IsKind(SyntaxKind.Attribute)))
+                .Single();
+
+            Assert.Null(model.GetSymbolInfo(node).Symbol);
+        }
     }
 }