Specially handle more scenarios for type parameters with 'allows ref …

…struct' constraint (#73232)

Also related to #73242.

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

@@ -1872,7 +1872,7 @@ private BoundExpression SynthesizeMethodGroupReceiver(CSharpSyntaxNode syntax, A
 
         private bool IsBadLocalOrParameterCapture(Symbol symbol, TypeSymbol type, RefKind refKind)
         {
-            if (refKind != RefKind.None || type.IsRestrictedType()) // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+            if (refKind != RefKind.None || type.IsRestrictedType())
             {
                 var containingMethod = this.ContainingMemberOrLambda as MethodSymbol;
                 if ((object)containingMethod != null && (object)symbol.ContainingSymbol != (object)containingMethod)
@@ -2046,7 +2046,7 @@ private BoundExpression BindNonMethod(SimpleNameSyntax node, Symbol symbol, Bind
                                 }
                                 else
                                 {
-                                    Debug.Assert(parameter.Type.IsRefLikeType); // PROTOTYPE(RefStructInterfaces): adjust?
+                                    Debug.Assert(parameter.Type.IsRefLikeTypeOrAllowsByRefLike());
                                     Error(diagnostics, ErrorCode.ERR_AnonDelegateCantUseRefLike, node, parameter.Name);
                                 }
                             }
@@ -2056,7 +2056,7 @@ private BoundExpression BindNonMethod(SimpleNameSyntax node, Symbol symbol, Bind
                                 bool capture = (this.ContainingMember() is MethodSymbol containingMethod && (object)primaryCtor != containingMethod);
 
                                 if (capture &&
-                                    (parameter.RefKind != RefKind.None || parameter.Type.IsRestrictedType()) && // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+                                    (parameter.RefKind != RefKind.None || parameter.Type.IsRestrictedType()) &&
                                     !IsInsideNameof)
                                 {
                                     if (parameter.RefKind != RefKind.None)
@@ -2069,7 +2069,7 @@ private BoundExpression BindNonMethod(SimpleNameSyntax node, Symbol symbol, Bind
                                     }
                                     else
                                     {
-                                        Debug.Assert(parameter.Type.IsRefLikeType); // PROTOTYPE(RefStructInterfaces): adjust?
+                                        Debug.Assert(parameter.Type.IsRefLikeTypeOrAllowsByRefLike());
                                         Error(diagnostics, ErrorCode.ERR_UnsupportedPrimaryConstructorParameterCapturingRefLike, node, parameter.Name);
                                     }
                                 }
@@ -3187,7 +3187,7 @@ internal static void CheckRestrictedTypeInAsyncMethod(Symbol containingSymbol, T
             Debug.Assert(errorCode is ErrorCode.ERR_BadSpecialByRefLocal or ErrorCode.ERR_BadSpecialByRefUsing or ErrorCode.ERR_BadSpecialByRefLock);
             if (containingSymbol.Kind == SymbolKind.Method
                 && ((MethodSymbol)containingSymbol).IsAsync
-                && type.IsRestrictedType()) // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+                && type.IsRestrictedType())
             {
                 if (errorCode == ErrorCode.ERR_BadSpecialByRefLock)
                 {

src/Compilers/CSharp/Portable/Binder/Binder_Operators.cs

@@ -3566,10 +3566,37 @@ internal static ConstantValue GetIsOperatorConstantResult(
                         return ConstantValue.False;
                     }
 
-                    // * If either type is a restricted type, the type check isn't supported because
+                    // * If either type is a restricted type, the type check isn't supported for some scenarios because
                     //   a restricted type cannot be boxed or unboxed into.
-                    if (targetType.IsRestrictedType() || operandType.IsRestrictedType()) // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+                    if (targetType.IsRestrictedType() || operandType.IsRestrictedType())
                     {
+                        if (targetType is TypeParameterSymbol { AllowByRefLike: true })
+                        {
+                            if (!operandType.IsRefLikeType && operandType is not TypeParameterSymbol)
+                            {
+                                return null;
+                            }
+                        }
+                        else if (operandType is not TypeParameterSymbol { AllowByRefLike: true })
+                        {
+                            if (targetType.IsRefLikeType)
+                            {
+                                if (operandType is TypeParameterSymbol)
+                                {
+                                    Debug.Assert(operandType is TypeParameterSymbol { AllowByRefLike: false });
+                                    return ConstantValue.False;
+                                }
+                            }
+                            else if (operandType.IsRefLikeType)
+                            {
+                                if (targetType is TypeParameterSymbol)
+                                {
+                                    Debug.Assert(targetType is TypeParameterSymbol { AllowByRefLike: false });
+                                    return ConstantValue.False;
+                                }
+                            }
+                        }
+
                         return ConstantValue.Bad;
                     }
 
@@ -3981,6 +4008,11 @@ internal static ConstantValue GetAsOperatorConstantResult(TypeSymbol operandType
 
                 if (!isOperatorConstantResult.BooleanValue)
                 {
+                    if (operandType?.IsRefLikeType == true)
+                    {
+                        return ConstantValue.Bad;
+                    }
+
                     return ConstantValue.Null;
                 }
             }

src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs

@@ -752,7 +752,6 @@ internal MethodSymbol TryFindDisposePatternMethod(BoundExpression expr, SyntaxNo
         {
             Debug.Assert(expr is object);
             Debug.Assert(expr.Type is object);
-            // PROTOTYPE(RefStructInterfaces): adjust?
             Debug.Assert(expr.Type.IsRefLikeType || hasAwait); // pattern dispose lookup is only valid on ref structs or asynchronous usings
 
             var result = PerformPatternMethodLookup(expr,

src/Compilers/CSharp/Portable/BoundTree/UnboundLambda.cs

@@ -669,7 +669,7 @@ private static TypeWithAnnotations DelegateReturnTypeWithAnnotations(MethodSymbo
                             getEffectiveScopeFromSymbol = true;
                         }
                     }
-                    else if (type.IsRefLikeType() && ParameterSyntax(i)?.Modifiers.Any(SyntaxKind.ParamsKeyword) == true) // PROTOTYPE(RefStructInterfaces): adjust?
+                    else if (type.IsRefLikeTypeOrAllowsByRefLike() && ParameterSyntax(i)?.Modifiers.Any(SyntaxKind.ParamsKeyword) == true)
                     {
                         scope = ScopedKind.ScopedValue;
                         if (_unboundLambda.ParameterAttributes(i).Any())

src/Compilers/CSharp/Portable/CodeGen/EmitExpression.cs

@@ -3989,7 +3989,7 @@ private void EmitStaticCast(TypeSymbol to, SyntaxNode syntax)
 
         private void EmitBox(TypeSymbol type, SyntaxNode syntaxNode)
         {
-            Debug.Assert(!type.IsRefLikeType); // PROTOTYPE(RefStructInterfaces): adjust?
+            Debug.Assert(!type.IsRefLikeType);
 
             _builder.EmitOpCode(ILOpCode.Box);
             EmitSymbolToken(type, syntaxNode);

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

@@ -11784,7 +11784,7 @@ protected override void VisitInterpolatedStringHandlerConstructor(BoundExpressio
 
         public override BoundNode? VisitStackAllocArrayCreation(BoundStackAllocArrayCreation node)
         {
-            Debug.Assert(node.Type is null || node.Type.IsErrorType() || node.Type.IsRefLikeType); // PROTOTYPE(RefStructInterfaces): adjust?
+            Debug.Assert(node.Type is null || node.Type.IsErrorType() || node.Type.IsRefLikeType);
             return VisitStackAllocArrayCreationBase(node);
         }
 

src/Compilers/CSharp/Portable/Lowering/ClosureConversion/ClosureConversion.Analysis.Tree.cs

@@ -695,8 +695,9 @@ private void AddDiagnosticIfRestrictedType(Symbol capturedVariable, SyntaxNode s
                             return;
                     }
 
-                    if (type.IsRestrictedType() == true) // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+                    if (type.IsRestrictedType() == true)
                     {
+                        Debug.Assert(false); // Add test(s) for scenarios that hit this code path
                         _diagnostics.Add(ErrorCode.ERR_SpecialByRefInLambda, syntax.Location, type);
                     }
                 }

src/Compilers/CSharp/Portable/Lowering/Instrumentation/LocalStateTracingInstrumenter.cs

@@ -234,8 +234,10 @@ _ when variableType.IsPointerOrFunctionPointer()
                         => WellKnownMember.Microsoft_CodeAnalysis_Runtime_LocalStoreTracker__LogLocalStorePointer,
                     _ when !variableType.IsManagedTypeNoUseSiteDiagnostics
                         => WellKnownMember.Microsoft_CodeAnalysis_Runtime_LocalStoreTracker__LogLocalStoreUnmanaged,
-                    _ when variableType.IsRefLikeType && !hasOverriddenToString(variableType) // PROTOTYPE(RefStructInterfaces): adjust?
+                    _ when variableType.IsRefLikeType && !hasOverriddenToString(variableType)
                         => null, // not possible to invoke ToString on ref struct that doesn't override it
+                    _ when variableType is TypeParameterSymbol { AllowByRefLike: true }
+                        => null, // not possible to invoke ToString on ref struct type parameter
                     _ when variableType.TypeKind is TypeKind.Struct
                         // we'll emit ToString constrained virtcall to avoid boxing the struct
                         => WellKnownMember.Microsoft_CodeAnalysis_Runtime_LocalStoreTracker__LogLocalStoreString,

src/Compilers/CSharp/Portable/Lowering/SpillSequenceSpiller.cs

@@ -334,7 +334,7 @@ private BoundExpression Spill(
                         continue;
 
                     case BoundKind.Sequence:
-                        if (refKind != RefKind.None || expression.Type?.IsRefLikeType == true) // PROTOTYPE(RefStructInterfaces): adjust?
+                        if (refKind != RefKind.None || expression.Type?.IsRefLikeTypeOrAllowsByRefLike() == true)
                         {
                             var sequence = (BoundSequence)expression;
 

src/Compilers/CSharp/Portable/Lowering/StateMachineRewriter/IteratorAndAsyncCaptureWalker.cs

@@ -125,11 +125,11 @@ private static bool HoistInDebugBuild(Symbol symbol)
             {
                 ParameterSymbol parameter =>
                     // in Debug build hoist all parameters that can be hoisted:
-                    !parameter.Type.IsRestrictedType(), // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+                    !parameter.Type.IsRestrictedType(),
                 LocalSymbol { IsConst: false, IsPinned: false, IsRef: false } local =>
                     // hoist all user-defined locals and long-lived temps that can be hoisted:
                     local.SynthesizedKind.MustSurviveStateMachineSuspension() &&
-                    !local.Type.IsRestrictedType(), // PROTOTYPE(RefStructInterfaces): Is this doing the right thing for 'allows ref struct' type parameters? 
+                    !local.Type.IsRestrictedType(),
                 _ => false
             };
         }

src/Compilers/CSharp/Portable/Symbols/AnonymousTypes/AnonymousTypeField.cs

@@ -43,7 +43,6 @@ public AnonymousTypeField(
             bool isParams = false,
             bool hasUnscopedRefAttribute = false)
         {
-            Debug.Assert(!isParams || !typeWithAnnotations.Type.IsTypeParameter());
             this.Name = name;
             this.Location = location;
             this.TypeWithAnnotations = typeWithAnnotations;

src/Compilers/CSharp/Portable/Symbols/TypeWithAnnotations.cs

@@ -278,6 +278,8 @@ public bool IsSZArray() =>
             _extensions.IsSZArray(DefaultType);
         public bool IsRefLikeType() =>
             _extensions.IsRefLikeType(DefaultType);
+        public bool IsRefLikeTypeOrAllowsByRefLike() =>
+            _extensions.IsRefLikeTypeOrAllowsByRefLike(DefaultType);
         public bool IsStatic =>
             _extensions.IsStatic(DefaultType);
         public bool IsRestrictedType(bool ignoreSpanLikeTypes = false) =>
@@ -865,6 +867,7 @@ internal static Extensions Create(ImmutableArray<CustomModifier> customModifiers
             internal abstract bool IsVoid(TypeSymbol typeSymbol);
             internal abstract bool IsSZArray(TypeSymbol typeSymbol);
             internal abstract bool IsRefLikeType(TypeSymbol typeSymbol);
+            internal abstract bool IsRefLikeTypeOrAllowsByRefLike(TypeSymbol typeSymbol);
 
             internal abstract TypeWithAnnotations WithTypeAndModifiers(TypeWithAnnotations type, TypeSymbol typeSymbol, ImmutableArray<CustomModifier> customModifiers);
 
@@ -896,6 +899,7 @@ public NonLazyType(ImmutableArray<CustomModifier> customModifiers)
             internal override bool IsVoid(TypeSymbol typeSymbol) => typeSymbol.IsVoidType();
             internal override bool IsSZArray(TypeSymbol typeSymbol) => typeSymbol.IsSZArray();
             internal override bool IsRefLikeType(TypeSymbol typeSymbol) => typeSymbol.IsRefLikeType;
+            internal override bool IsRefLikeTypeOrAllowsByRefLike(TypeSymbol typeSymbol) => typeSymbol.IsRefLikeTypeOrAllowsByRefLike();
 
             internal override TypeSymbol GetNullableUnderlyingTypeOrSelf(TypeSymbol typeSymbol) => typeSymbol.StrippedType();
 
@@ -968,6 +972,7 @@ public LazySubstitutedType(ImmutableArray<CustomModifier> customModifiers, TypeP
             internal override bool IsVoid(TypeSymbol typeSymbol) => typeSymbol.IsVoidType();
             internal override bool IsSZArray(TypeSymbol typeSymbol) => typeSymbol.IsSZArray();
             internal override bool IsRefLikeType(TypeSymbol typeSymbol) => typeSymbol.IsRefLikeType;
+            internal override bool IsRefLikeTypeOrAllowsByRefLike(TypeSymbol typeSymbol) => typeSymbol.IsRefLikeTypeOrAllowsByRefLike();
 
             internal override NullableAnnotation GetResolvedAnnotation(NullableAnnotation defaultAnnotation)
             {
@@ -1068,6 +1073,7 @@ public LazyNullableTypeParameter(CSharpCompilation compilation, TypeWithAnnotati
             internal override bool IsVoid(TypeSymbol typeSymbol) => false;
             internal override bool IsSZArray(TypeSymbol typeSymbol) => false;
             internal override bool IsRefLikeType(TypeSymbol typeSymbol) => false;
+            internal override bool IsRefLikeTypeOrAllowsByRefLike(TypeSymbol typeSymbol) => typeSymbol.IsRefLikeTypeOrAllowsByRefLike();
             internal override bool IsStatic(TypeSymbol typeSymbol) => false;
 
             private TypeSymbol GetResolvedType()

src/Compilers/CSharp/Test/Emit2/Emit/LocalStateTracing/LocalStateTracingTests.cs

@@ -162,7 +162,7 @@ private static string MemoryToString(void* address, int size)
         private static string WithHelpers(string source)
             => source + s_helpers;
 
-        private static readonly TargetFramework s_targetFramework = TargetFramework.Net70;
+        private const TargetFramework s_targetFramework = TargetFramework.Net70;
 
         private static readonly Verification s_verification = Verification.Fails with
         {
@@ -180,13 +180,13 @@ private static string WithHelpers(string source)
             """
         };
 
-        private CompilationVerifier CompileAndVerify(string source, string? ilVerifyMessage = null, string? expectedOutput = null)
+        private CompilationVerifier CompileAndVerify(string source, string? ilVerifyMessage = null, string? expectedOutput = null, TargetFramework targetFramework = s_targetFramework)
             => CompileAndVerify(
                 source,
                 options: (expectedOutput != null) ? TestOptions.UnsafeDebugExe : TestOptions.UnsafeDebugDll,
                 emitOptions: s_emitOptions,
                 verify: s_verification with { ILVerifyMessage = ilVerifyMessage + Environment.NewLine + s_verification.ILVerifyMessage },
-                targetFramework: s_targetFramework,
+                targetFramework: targetFramework,
                 expectedOutput: expectedOutput);
 
         // Only used to diagnose test verification failures (rename CompileAndVerify to CompileAndVerifyFails and rerun).
@@ -1682,6 +1682,82 @@ .locals init (Microsoft.CodeAnalysis.Runtime.LocalStoreTracker V_0,
 }");
         }
 
+        [Fact]
+        public void RefStructTypeParameter()
+        {
+            var source = WithHelpers("""
+S.F(new S());
+
+ref struct S
+{
+    ref int X;
+
+    public static void F<T>(T p)
+        where T : struct, allows ref struct
+    {
+        int a = 1;
+        var x = p = default(T);
+    }
+}
+""");
+            var verifier = CompileAndVerify(
+                source,
+                targetFramework: TargetFramework.Net80, // PROTOTYPE(RefStructInterfaces): Switch to supporting target framework once we have its ref assemblies.
+                expectedOutput: @"
+<Main>$: Entered
+<Main>$: P'args'[0] = System.String[]
+F: Entered
+F: L1 = 1
+F: Returned
+<Main>$: Returned
+");
+
+            // writes to x and p are not logged since we can't invoke ToString()
+            verifier.VerifyMethodBody("S.F<T>(T)", @"
+{
+  // Code size       46 (0x2e)
+  .maxstack  3
+  .locals init (Microsoft.CodeAnalysis.Runtime.LocalStoreTracker V_0,
+            int V_1, //a
+            T V_2) //x
+  // sequence point: <hidden>
+  IL_0000:  ldtoken    ""void S.F<T>(T)""
+  IL_0005:  call       ""Microsoft.CodeAnalysis.Runtime.LocalStoreTracker Microsoft.CodeAnalysis.Runtime.LocalStoreTracker.LogMethodEntry(int)""
+  IL_000a:  stloc.0
+  .try
+  {
+    // sequence point: {
+    IL_000b:  nop
+    // sequence point: int a = 1;
+    IL_000c:  ldloca.s   V_0
+    IL_000e:  ldc.i4.1
+    IL_000f:  dup
+    IL_0010:  stloc.1
+    IL_0011:  ldc.i4.1
+    IL_0012:  call       ""void Microsoft.CodeAnalysis.Runtime.LocalStoreTracker.LogLocalStore(uint, int)""
+    IL_0017:  nop
+    // sequence point: var x = p = default(T);
+    IL_0018:  ldarga.s   V_0
+    IL_001a:  initobj    ""T""
+    IL_0020:  ldarg.0
+    IL_0021:  stloc.2
+    // sequence point: }
+    IL_0022:  leave.s    IL_002d
+  }
+  finally
+  {
+    // sequence point: <hidden>
+    IL_0024:  ldloca.s   V_0
+    IL_0026:  call       ""void Microsoft.CodeAnalysis.Runtime.LocalStoreTracker.LogReturn()""
+    IL_002b:  nop
+    IL_002c:  endfinally
+  }
+  // sequence point: }
+  IL_002d:  ret
+}
+");
+        }
+
         [Fact]
         public void UnmanagedRefStruct()
         {