merge features/nested-stackalloc (#35385)

* Permit stackalloc in nested contexts. (#28969)
Fixes #26759

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

@@ -3413,14 +3413,17 @@ private BoundExpression BindStackAllocArrayCreationExpression(
         private bool ReportBadStackAllocPosition(SyntaxNode node, DiagnosticBag diagnostics)
         {
             Debug.Assert(node is StackAllocArrayCreationExpressionSyntax || node is ImplicitStackAllocArrayCreationExpressionSyntax);
+            bool inLegalPosition = true;
 
-            var inLegalPosition = (IsInMethodBody || IsLocalFunctionsScopeBinder) && node.IsLegalSpanStackAllocPosition();
-            if (!inLegalPosition)
+            // If we are using a language version that does not restrict the position of a stackalloc expression, skip that test.
+            LanguageVersion requiredVersion = MessageID.IDS_FeatureNestedStackalloc.RequiredVersion();
+            if (requiredVersion > Compilation.LanguageVersion)
             {
-                diagnostics.Add(
-                    ErrorCode.ERR_InvalidExprTerm,
-                    node.GetFirstToken().GetLocation(),
-                    SyntaxFacts.GetText(SyntaxKind.StackAllocKeyword));
+                inLegalPosition = (IsInMethodBody || IsLocalFunctionsScopeBinder) && node.IsLegalCSharp73SpanStackAllocPosition();
+                if (!inLegalPosition)
+                {
+                    MessageID.IDS_FeatureNestedStackalloc.CheckFeatureAvailability(diagnostics, node.GetFirstToken().GetLocation());
+                }
             }
 
             // Check if we're syntactically within a catch or finally clause.
@@ -3436,7 +3439,7 @@ private TypeSymbol GetStackAllocType(SyntaxNode node, TypeWithAnnotations elemen
         {
             var inLegalPosition = ReportBadStackAllocPosition(node, diagnostics);
             hasErrors = !inLegalPosition;
-            if (inLegalPosition && !node.IsVariableDeclarationInitialization())
+            if (inLegalPosition && !node.IsLocalVariableDeclarationInitializationForPointerStackalloc())
             {
                 CheckFeatureAvailability(node, MessageID.IDS_FeatureRefStructs, diagnostics);
 
@@ -5809,9 +5812,8 @@ private BoundExpression BindMemberAccessWithBoundLeft(
                         }
                     default:
                         {
-                            // Can't dot into the null literal or stackalloc expressions.
-                            if ((boundLeft.Kind == BoundKind.Literal && ((BoundLiteral)boundLeft).ConstantValueOpt == ConstantValue.Null) ||
-                                boundLeft.Kind == BoundKind.StackAllocArrayCreation)
+                            // Can't dot into the null literal
+                            if (boundLeft.Kind == BoundKind.Literal && ((BoundLiteral)boundLeft).ConstantValueOpt == ConstantValue.Null)
                             {
                                 if (!boundLeft.HasAnyErrors)
                                 {

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

@@ -825,7 +825,9 @@ protected BoundExpression BindInferredVariableInitializer(DiagnosticBag diagnost
 
             BoundExpression expression = BindValue(initializer, diagnostics, valueKind);
 
-            if (expression is BoundStackAllocArrayCreation boundStackAlloc)
+            if (expression is BoundStackAllocArrayCreation boundStackAlloc &&
+                initializer.IsLocalVariableDeclarationInitializationForPointerStackalloc() &&
+                (initializer.Kind() == SyntaxKind.StackAllocArrayCreationExpression || initializer.Kind() == SyntaxKind.ImplicitStackAllocArrayCreationExpression))
             {
                 var type = new PointerTypeSymbol(TypeWithAnnotations.Create(boundStackAlloc.ElementType));
                 expression = GenerateConversionForAssignment(type, boundStackAlloc, diagnostics, isRefAssignment: refKind != RefKind.None);

src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/Conversions.cs

@@ -304,7 +304,7 @@ private static Conversion ToConversion(OverloadResolutionResult<MethodSymbol> re
 
         public override Conversion GetStackAllocConversion(BoundStackAllocArrayCreation sourceExpression, TypeSymbol destination, ref HashSet<DiagnosticInfo> useSiteDiagnostics)
         {
-            if (sourceExpression.Syntax.IsVariableDeclarationInitialization())
+            if (sourceExpression.Syntax.IsLocalVariableDeclarationInitializationForPointerStackalloc())
             {
                 Debug.Assert((object)sourceExpression.Type == null);
                 Debug.Assert((object)sourceExpression.ElementType != null);

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

@@ -0,0 +1,30 @@
+// 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 Microsoft.CodeAnalysis.CSharp.Symbols;
+using Microsoft.CodeAnalysis.PooledObjects;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Microsoft.CodeAnalysis.CSharp
+{
+    internal partial class BoundSpillSequence
+    {
+        public BoundSpillSequence(
+            SyntaxNode syntax,
+            ImmutableArray<LocalSymbol> locals,
+            ImmutableArray<BoundExpression> sideEffects,
+            BoundExpression value,
+            TypeSymbol type,
+            bool hasErrors = false)
+            : this(syntax, locals, MakeStatements(sideEffects), value, type, hasErrors)
+        {
+        }
+
+        private static ImmutableArray<BoundStatement> MakeStatements(ImmutableArray<BoundExpression> expressions)
+        {
+            return expressions.SelectAsArray<BoundExpression, BoundStatement>(
+                expression => new BoundExpressionStatement(expression.Syntax, expression, expression.HasErrors));
+        }
+    }
+}

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

@@ -150,7 +150,7 @@ public override object Display
     internal partial class BoundStackAllocArrayCreation
     {
         public override object Display
-            => FormattableStringFactory.Create("stackalloc {0}[{1}]", ElementType, Count.WasCompilerGenerated ? null : Count.Syntax.ToString());
+            => (Type is null) ? FormattableStringFactory.Create("stackalloc {0}[{1}]", ElementType, Count.WasCompilerGenerated ? null : Count.Syntax.ToString()) : base.Display;
     }
 
     internal partial class BoundPassByCopy

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -5916,4 +5916,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="WRN_NullabilityMismatchInConstraintsOnPartialImplementation_Title" xml:space="preserve">
     <value>Partial method declarations have inconsistent nullability in constraints for type parameter</value>
   </data>
+  <data name="IDS_FeatureNestedStackalloc" xml:space="preserve">
+    <value>stackalloc in nested expressions</value>
+  </data>
 </root>

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

@@ -180,6 +180,7 @@ internal enum MessageID
         IDS_DefaultInterfaceImplementation = MessageBase + 12760,
         IDS_BaseTypeInBaseExpression = MessageBase + 12761,
         IDS_OverrideWithConstraints = MessageBase + 12762,
+        IDS_FeatureNestedStackalloc = MessageBase + 12763,
     }
 
     // Message IDs may refer to strings that need to be localized.
@@ -289,6 +290,7 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
                 case MessageID.IDS_DefaultInterfaceImplementation: // semantic check
                 case MessageID.IDS_BaseTypeInBaseExpression:
                 case MessageID.IDS_OverrideWithConstraints: // semantic check
+                case MessageID.IDS_FeatureNestedStackalloc: // semantic check
                     return LanguageVersion.CSharp8;
 
                 // C# 7.3 features.

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_Await.cs

@@ -40,14 +40,12 @@ private BoundExpression RewriteAwaitExpression(BoundExpression rewrittenAwait, b
             // The resulting nodes will be "spilled" to move such statements to the top
             // level (i.e. into the enclosing statement list).
             _needsSpilling = true;
-            BoundLocal replacement = _factory.StoreToTemp(
-                rewrittenAwait, out BoundAssignmentOperator saveToTemp, kind: SynthesizedLocalKind.Spill, syntaxOpt: rewrittenAwait.Syntax);
             return new BoundSpillSequence(
                 syntax: rewrittenAwait.Syntax,
-                locals: ImmutableArray.Create<LocalSymbol>(replacement.LocalSymbol),
-                sideEffects: ImmutableArray.Create<BoundStatement>(_factory.ExpressionStatement(saveToTemp)),
-                value: replacement,
-                type: replacement.Type);
+                locals: ImmutableArray<LocalSymbol>.Empty,
+                sideEffects: ImmutableArray<BoundStatement>.Empty,
+                value: rewrittenAwait,
+                type: rewrittenAwait.Type);
         }
     }
 }

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_BinaryOperator.cs

@@ -1326,12 +1326,16 @@ private BoundExpression LowerLiftedBinaryArithmeticOperator(
                 type: type);
         }
 
-        private BoundExpression CaptureExpressionInTempIfNeeded(BoundExpression operand, ArrayBuilder<BoundExpression> sideeffects, ArrayBuilder<LocalSymbol> locals)
+        private BoundExpression CaptureExpressionInTempIfNeeded(
+            BoundExpression operand,
+            ArrayBuilder<BoundExpression> sideeffects,
+            ArrayBuilder<LocalSymbol> locals,
+            SynthesizedLocalKind kind = SynthesizedLocalKind.LoweringTemp)
         {
             if (CanChangeValueBetweenReads(operand))
             {
                 BoundAssignmentOperator tempAssignment;
-                var tempAccess = _factory.StoreToTemp(operand, out tempAssignment);
+                var tempAccess = _factory.StoreToTemp(operand, out tempAssignment, kind: kind);
                 sideeffects.Add(tempAssignment);
                 locals.Add(tempAccess.LocalSymbol);
                 operand = tempAccess;

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_StackAlloc.cs

@@ -44,7 +44,7 @@ public override BoundNode VisitStackAllocArrayCreation(BoundStackAllocArrayCreat
                 var spanType = (NamedTypeSymbol)stackAllocNode.Type;
                 var sideEffects = ArrayBuilder<BoundExpression>.GetInstance();
                 var locals = ArrayBuilder<LocalSymbol>.GetInstance();
-                var countTemp = CaptureExpressionInTempIfNeeded(rewrittenCount, sideEffects, locals);
+                var countTemp = CaptureExpressionInTempIfNeeded(rewrittenCount, sideEffects, locals, SynthesizedLocalKind.Spill);
                 var stackSize = RewriteStackAllocCountToSize(countTemp, elementType);
                 stackAllocNode = new BoundConvertedStackAllocExpression(stackAllocNode.Syntax, elementType, stackSize, initializerOpt, spanType);
 
@@ -63,7 +63,8 @@ public override BoundNode VisitStackAllocArrayCreation(BoundStackAllocArrayCreat
                         type: ErrorTypeSymbol.UnknownResultType);
                 }
 
-                return new BoundSequence(
+                _needsSpilling = true;
+                return new BoundSpillSequence(
                     syntax: stackAllocNode.Syntax,
                     locals: locals.ToImmutableAndFree(),
                     sideEffects: sideEffects.ToImmutableAndFree(),

src/Compilers/CSharp/Portable/Syntax/SyntaxNodeExtensions.cs

@@ -110,7 +110,12 @@ internal static bool IsValidScopeDesignator(this ExpressionSyntax expression)
             }
         }
 
-        internal static bool IsVariableDeclarationInitialization(this SyntaxNode node)
+        /// <summary>
+        /// Is this a context in which a stackalloc expression could be converted to the corresponding pointer
+        /// type? The only context that permits it is the initialization of a local variable declaration (when
+        /// the declaration appears as a statement or as the first part of a for loop).
+        /// </summary>
+        internal static bool IsLocalVariableDeclarationInitializationForPointerStackalloc(this SyntaxNode node)
         {
             Debug.Assert(node != null);
 
@@ -128,15 +133,25 @@ internal static bool IsVariableDeclarationInitialization(this SyntaxNode node)
                 return false;
             }
 
-            return variableDeclarator.Parent.IsKind(SyntaxKind.VariableDeclaration);
+            SyntaxNode variableDeclaration = variableDeclarator.Parent;
+            if (!variableDeclaration.IsKind(SyntaxKind.VariableDeclaration))
+            {
+                return false;
+            }
+
+            return
+                variableDeclaration.Parent.IsKind(SyntaxKind.LocalDeclarationStatement) ||
+                variableDeclaration.Parent.IsKind(SyntaxKind.ForStatement);
         }
 
         /// <summary>
-        /// Because the instruction cannot have any values on the stack before CLR execution.
-        /// Limit it to assignments and conditional expressions for now.
-        /// https://github.com/dotnet/roslyn/issues/22046
+        /// Because the instruction cannot have any values on the stack before CLR execution
+        /// we limited it to assignments and conditional expressions in C# 7.
+        /// See https://github.com/dotnet/roslyn/issues/22046.
+        /// In C# 8 we relaxed
+        /// that by rewriting the code to move it to the statement level where the stack is empty.
         /// </summary>
-        internal static bool IsLegalSpanStackAllocPosition(this SyntaxNode node)
+        internal static bool IsLegalCSharp73SpanStackAllocPosition(this SyntaxNode node)
         {
             Debug.Assert(node != null);
 

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

@@ -802,6 +802,11 @@
         <target state="translated">skrývání názvů ve vnořených funkcích</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">typy odkazů s možnou hodnotou null</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">Namensshadowing in geschachtelten Funktionen</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">Nullable-Verweistypen</target>

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

@@ -804,6 +804,11 @@
         <target state="translated">sombreado de nombres en funciones anidadas</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">tipos de referencia que aceptan valores NULL</target>

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

@@ -803,6 +803,11 @@
         <target state="translated">ombrage des noms dans les fonctions imbriquées</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">types référence Nullable</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">shadowing dei nomi nelle funzioni annidate</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">tipi riferimento nullable</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">入れ子になった関数での名前シャドウイング</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">Null 許容参照型</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">중첩된 함수의 이름 섀도잉</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">nullable 참조 형식</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">zasłanianie nazw w funkcjach zagnieżdżonych</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">typy referencyjne dopuszczające wartość null</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">sombreamento de nome em funções aninhadas</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">tipos de referência que permitem valor nulo</target>

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

@@ -802,6 +802,11 @@
         <target state="translated">скрытие имен во вложенных функциях</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">ссылочные типы, допускающие значение NULL</target>

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

@@ -803,6 +803,11 @@
         <target state="translated">iç içe işlevlerde ad gölgeleme</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">boş değer atanabilir başvuru türleri</target>

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

@@ -843,6 +843,11 @@
         <target state="translated">在嵌套函数中的名称映射</target>
         <note />
       </trans-unit>
+      <trans-unit id="IDS_FeatureNestedStackalloc">
+        <source>stackalloc in nested expressions</source>
+        <target state="new">stackalloc in nested expressions</target>
+        <note />
+      </trans-unit>
       <trans-unit id="IDS_FeatureNullableReferenceTypes">
         <source>nullable reference types</source>
         <target state="translated">可为 null 的引用类型</target>