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michaelnebelmichaelnebel
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Merge pull request #21309 from michaelnebel/csharp14/field
C# 14: Support the `field` keyword.
2 parents 94e3d86 + c3a1eb1 commit fa27eaa

11 files changed

Lines changed: 432 additions & 2 deletions

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‎csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/Factory.cs‎

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@@ -160,6 +160,9 @@ internal static Expression Create(ExpressionNodeInfo info)
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case SyntaxKind.ThisExpression:
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return This.CreateExplicit(info);
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case SyntaxKind.FieldExpression:
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return PropertyFieldAccess.Create(info);
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case SyntaxKind.AddressOfExpression:
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return Unary.Create(info.SetKind(ExprKind.ADDRESS_OF));
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‎csharp/extractor/Semmle.Extraction.CSharp/Entities/Expressions/PropertyFieldAccess.cs‎

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using System.IO;
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using Microsoft.CodeAnalysis;
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using Microsoft.CodeAnalysis.CSharp.Syntax;
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using Semmle.Extraction.Kinds;
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namespace Semmle.Extraction.CSharp.Entities.Expressions
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{
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internal class PropertyFieldAccess : Expression<FieldExpressionSyntax>
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{
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private PropertyFieldAccess(ExpressionNodeInfo info) : base(info.SetKind(ExprKind.FIELD_ACCESS)) { }
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public static Expression Create(ExpressionNodeInfo info) => new PropertyFieldAccess(info).TryPopulate();
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protected override void PopulateExpression(TextWriter trapFile)
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{
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var symbolInfo = Context.GetSymbolInfo(Syntax);
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if (symbolInfo.Symbol is IFieldSymbol field)
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{
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var target = PropertyField.Create(Context, field);
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trapFile.expr_access(this, target);
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if (!field.IsStatic)
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{
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This.CreateImplicit(Context, field.ContainingType, Location, this, -1);
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}
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}
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}
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}
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}

‎csharp/extractor/Semmle.Extraction.CSharp/Entities/Field.cs‎

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@@ -10,7 +10,7 @@ namespace Semmle.Extraction.CSharp.Entities
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{
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internal class Field : CachedSymbol<IFieldSymbol>, IExpressionParentEntity
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{
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private Field(Context cx, IFieldSymbol init)
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protected Field(Context cx, IFieldSymbol init)
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: base(cx, init)
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{
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type = new Lazy<Type>(() => Entities.Type.Create(cx, Symbol.Type));

‎csharp/extractor/Semmle.Extraction.CSharp/Entities/PropertyField.cs‎

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@@ -0,0 +1,53 @@
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using System.IO;
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using Microsoft.CodeAnalysis;
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using Semmle.Extraction.CSharp.Util;
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using Semmle.Extraction.Kinds;
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namespace Semmle.Extraction.CSharp.Entities
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{
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/// <summary>
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/// Represents the autogenerated backing field `field` for a property.
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/// It is only created for properties that use the `field` keyword in their getter or setter, and
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/// is not created for auto-properties.
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/// </summary>
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internal class PropertyField : Field
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{
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protected PropertyField(Context cx, IFieldSymbol init)
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: base(cx, init)
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{
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}
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public static new PropertyField Create(Context cx, IFieldSymbol field) => PropertyFieldFactory.Instance.CreateEntity(cx, (field, field.AssociatedSymbol), field);
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public override bool NeedsPopulation => true;
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public override void Populate(TextWriter trapFile)
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{
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PopulateNullability(trapFile, Symbol.GetAnnotatedType());
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var unboundFieldKey = PropertyField.Create(Context, Symbol.OriginalDefinition);
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var name = Symbol.AssociatedSymbol is not null ? $"{Symbol.AssociatedSymbol.GetName()}.field" : Symbol.Name;
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trapFile.fields(this, VariableKind.None, name, ContainingType!, Type.TypeRef, unboundFieldKey);
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trapFile.compiler_generated(this);
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PopulateModifiers(trapFile);
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if (Context.OnlyScaffold)
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{
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return;
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}
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if (Context.ExtractLocation(Symbol))
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{
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WriteLocationsToTrap(trapFile.field_location, this, Locations);
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}
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}
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private class PropertyFieldFactory : CachedEntityFactory<IFieldSymbol, PropertyField>
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{
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public static PropertyFieldFactory Instance { get; } = new PropertyFieldFactory();
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public override PropertyField Create(Context cx, IFieldSymbol init) => new PropertyField(cx, init);
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}
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}
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}

‎csharp/ql/lib/change-notes/2026-02-12-field-keyword.md‎

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---
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category: minorAnalysis
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---
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* C# 14: Added support for the `field` keyword in properties.

‎csharp/ql/test/library-tests/dataflow/fields/D.cs‎

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@@ -89,3 +89,65 @@ public static void Sink(object o) { }
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static T Source<T>(object source) => throw null;
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}
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public class DFieldProps
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{
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object FieldProp0
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{
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get { return field; }
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set { field = value; }
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} = Source<object>(0);
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object FieldProp1
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{
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get { return field; }
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set { field = value; }
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}
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object FieldProp2
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{
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get { return field; }
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set
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{
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var x = value;
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field = x;
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}
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}
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static object StaticFieldProp
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{
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get { return field; }
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set { field = value; }
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}
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private void M()
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{
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var d0 = new DFieldProps();
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Sink(d0.FieldProp0); // $ hasValueFlow=0
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Sink(d0.FieldProp1); // no flow
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Sink(d0.FieldProp2); // no flow
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var d1 = new DFieldProps();
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var o1 = Source<object>(1);
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d1.FieldProp1 = o1;
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Sink(d1.FieldProp0); // $ hasValueFlow=0
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Sink(d1.FieldProp1); // $ hasValueFlow=1
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Sink(d1.FieldProp2); // no flow
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var d2 = new DFieldProps();
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var o2 = Source<object>(2);
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d2.FieldProp2 = o2;
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Sink(d2.FieldProp0); // $ hasValueFlow=0
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Sink(d2.FieldProp1); // no flow
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Sink(d2.FieldProp2); // $ hasValueFlow=2
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var o3 = Source<object>(3);
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DFieldProps.StaticFieldProp = o3;
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Sink(DFieldProps.StaticFieldProp); // $ hasValueFlow=3
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}
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public static void Sink(object o) { }
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static T Source<T>(object source) => throw null;
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}

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