Field-backed properties: update uses of IsAutoProperty

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

@@ -1694,7 +1694,7 @@ private bool CheckPropertyValueKind(SyntaxNode node, BoundExpression expr, BindV
  if (setMethod is null)
  {
  var containing = this.ContainingMemberOrLambda;
- if (!AccessingAutoPropertyFromConstructor(receiver, propertySymbol, containing)
+ if (!AccessingAutoPropertyFromConstructor(receiver, propertySymbol, containing, allowFieldKeyword: true)
  && !isAllowedDespiteReadonly(receiver))
  {
  Error(diagnostics, ErrorCode.ERR_AssgReadonlyProp, node, propertySymbol);

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

@@ -1754,7 +1754,8 @@ internal static bool AccessingAutoPropertyFromConstructor(BoundPropertyAccess pr
  return AccessingAutoPropertyFromConstructor(propertyAccess.ReceiverOpt, propertyAccess.PropertySymbol, fromMember);
  }
 
- private static bool AccessingAutoPropertyFromConstructor(BoundExpression receiver, PropertySymbol propertySymbol, Symbol fromMember)
+ // PROTOTYPE: Review all callers for allowFieldKeyword.
+ private static bool AccessingAutoPropertyFromConstructor(BoundExpression receiver, PropertySymbol propertySymbol, Symbol fromMember, bool allowFieldKeyword = false)
  {
  if (!propertySymbol.IsDefinition && propertySymbol.ContainingType.Equals(propertySymbol.ContainingType.OriginalDefinition, TypeCompareKind.IgnoreNullableModifiersForReferenceTypes))
  {
@@ -1765,7 +1766,7 @@ private static bool AccessingAutoPropertyFromConstructor(BoundExpression receive
  var propertyIsStatic = propertySymbol.IsStatic;
 
  return (object)sourceProperty != null &&
- sourceProperty.IsAutoProperty &&
+ (allowFieldKeyword ? sourceProperty.IsAutoPropertyOrUsesFieldKeyword : sourceProperty.IsAutoProperty) &&
  TypeSymbol.Equals(sourceProperty.ContainingType, fromMember.ContainingType, TypeCompareKind.AllIgnoreOptions) &&
  IsConstructorOrField(fromMember, isStatic: propertyIsStatic) &&
  (propertyIsStatic || receiver.Kind == BoundKind.ThisReference);

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -4891,7 +4891,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
  <value>Expected identifier or numeric literal</value>
  </data>
  <data name="ERR_InitializerOnNonAutoProperty" xml:space="preserve">
- <value>Only auto-implemented properties can have initializers.</value>
+ <value>Only auto-implemented properties, or properties that use the 'field' keyword, can have initializers.</value>
  </data>
  <data name="ERR_InstancePropertyInitializerInInterface" xml:space="preserve">
  <value>Instance properties in interfaces cannot have initializers.</value>

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

@@ -281,8 +281,9 @@ private BoundExpression MakePropertyAssignment(
  if (setMethod is null)
  {
  var autoProp = (SourcePropertySymbolBase)property.OriginalDefinition;
- Debug.Assert(autoProp.IsAutoProperty,
+ Debug.Assert(autoProp.IsAutoPropertyOrUsesFieldKeyword,
  "only autoproperties can be assignable without having setters");
+ Debug.Assert(_factory.CurrentFunction.IsConstructor());
  Debug.Assert(property.Equals(autoProp, TypeCompareKind.IgnoreNullableModifiersForReferenceTypes));
 
  var backingField = autoProp.BackingField;

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

@@ -302,7 +302,7 @@ protected void CheckInitializerIfNeeded(BindingDiagnosticBag diagnostics)
  {
  diagnostics.Add(ErrorCode.ERR_InstancePropertyInitializerInInterface, Location);
  }
- else if (!IsAutoProperty)
+ else if (!IsAutoPropertyOrUsesFieldKeyword)
  {
  diagnostics.Add(ErrorCode.ERR_InitializerOnNonAutoProperty, Location);
  }
@@ -653,7 +653,7 @@ public bool HasSkipLocalsInitAttribute
  internal bool IsAutoPropertyOrUsesFieldKeyword
  => IsAutoProperty || UsesFieldKeyword;
 
- protected bool UsesFieldKeyword
+ private bool UsesFieldKeyword
  => (_propertyFlags & Flags.UsesFieldKeyword) != 0;
 
  protected bool HasExplicitAccessModifier
@@ -666,8 +666,9 @@ protected bool AccessorsHaveImplementation
  => (_propertyFlags & Flags.AccessorsHaveImplementation) != 0;
 
  /// <summary>
- /// Backing field for automatically implemented property, or
- /// for a property with an initializer.
+ /// Backing field for an automatically implemented property, or
+ /// a property with an accessor using the 'field' keyword, or
+ /// a property with an initializer.
  /// </summary>
  internal SynthesizedBackingFieldSymbol BackingField { get; }
 
@@ -715,9 +716,9 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
  diagnostics.Add(ErrorCode.ERR_RefReturningPropertiesCannotBeRequired, Location);
  }
 
- if (IsAutoProperty)
+ if (IsAutoPropertyOrUsesFieldKeyword)
  {
- if (!IsStatic && SetMethod is { IsInitOnly: false })
+ if (!IsStatic && ((_propertyFlags & Flags.HasAutoPropertySet) != 0) && SetMethod is { IsInitOnly: false })
  {
  if (ContainingType.IsReadOnly)
  {
@@ -738,10 +739,15 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
  diagnostics.Add(ErrorCode.ERR_AutoPropertyCannotBeRefReturning, Location);
  }
 
- // get-only auto property should not override settable properties
- if (this.IsOverride && SetMethod is null && !this.IsReadOnly)
+ // Auto property should override both accessors.
+ if (this.IsOverride)
  {
- diagnostics.Add(ErrorCode.ERR_AutoPropertyMustOverrideSet, Location);
+ var overriddenProperty = (PropertySymbol)this.GetLeastOverriddenMember(this.ContainingType);
+ if ((overriddenProperty.GetMethod is { } && GetMethod is null) ||
+ (overriddenProperty.SetMethod is { } && SetMethod is null))
+ {
+ diagnostics.Add(ErrorCode.ERR_AutoPropertyMustOverrideSet, Location);
+ }
  }
  }
 
@@ -791,6 +797,9 @@ internal override void AfterAddingTypeMembersChecks(ConversionsBase conversions,
  }
  else if (!hasGetAccessor && IsAutoProperty)
  {
+ // The only forms of auto-property that are disallowed are { set; } and { init; }.
+ // Other forms of auto- or manually-implemented accessors are allowed
+ // including equivalent field cases such as { set { field = value; } }.
  diagnostics.Add(ErrorCode.ERR_AutoPropertyMustHaveGetAccessor, _setMethod!.GetFirstLocation());
  }
 

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenRefLocalTests.cs

@@ -1761,7 +1761,7 @@ public void RefAssignStaticProperty()
 class Program
 {
  static int field = 0;
- static ref int P { get { return ref field; } }
+ static ref int P { get { return ref @field; } }
 
  static void M()
  {
@@ -1789,7 +1789,7 @@ public void RefAssignClassInstanceProperty()
 class Program
 {
  int field = 0;
- ref int P { get { return ref field; } }
+ ref int P { get { return ref @field; } }
 
  void M()
  {

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenRefReturnTests.cs

@@ -1258,7 +1258,7 @@ class Program
 {
  int field = 0;
 
- ref int P { get { return ref field; } }
+ ref int P { get { return ref @field; } }
 
  ref int this[int i] { get { return ref field; } }
 
@@ -1455,7 +1455,7 @@ class Program
 {
  int field = 0;
 
- ref int P { get { return ref field; } }
+ ref int P { get { return ref @field; } }
 
  ref int this[int i] { get { return ref field; } }