Fix regression with var pattern nullability (#53691)

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

@@ -208,7 +208,6 @@ protected override LocalState VisitSwitchStatementDispatch(BoundSwitchStatement
  // visit switch header
  Visit(node.Expression);
  var expressionState = ResultType;
- var initialState = PossiblyConditionalState.Create(this);
 
  DeclareLocals(node.InnerLocals);
  foreach (var section in node.SwitchSections)
@@ -217,7 +216,7 @@ protected override LocalState VisitSwitchStatementDispatch(BoundSwitchStatement
  DeclareLocals(section.Locals);
  }
 
- var labelStateMap = LearnFromDecisionDag(node.Syntax, node.DecisionDag, node.Expression, expressionState, ref initialState);
+ var labelStateMap = LearnFromDecisionDag(node.Syntax, node.DecisionDag, node.Expression, expressionState);
  foreach (var section in node.SwitchSections)
  {
  foreach (var label in section.SwitchLabels)
@@ -284,13 +283,11 @@ public PossiblyConditionalState Clone()
  }
  }
 
- private PooledDictionary<LabelSymbol, (LocalState state, bool believedReachable)>
- LearnFromDecisionDag(
+ private PooledDictionary<LabelSymbol, (LocalState state, bool believedReachable)> LearnFromDecisionDag(
  SyntaxNode node,
  BoundDecisionDag decisionDag,
  BoundExpression expression,
- TypeWithState expressionType,
- ref PossiblyConditionalState initialState)
+ TypeWithState expressionType)
  {
  // We reuse the slot at the beginning of a switch (or is-pattern expression), pretending that we are
  // not copying the input to evaluate the patterns. In this way we infer non-nullability of the original
@@ -319,7 +316,7 @@ public PossiblyConditionalState Clone()
  tempMap.Add(rootTemp, (originalInputSlot, expressionType.Type));
 
  var nodeStateMap = PooledDictionary<BoundDecisionDagNode, (PossiblyConditionalState state, bool believedReachable)>.GetInstance();
- nodeStateMap.Add(decisionDag.RootNode, (state: initialState.Clone(), believedReachable: true));
+ nodeStateMap.Add(decisionDag.RootNode, (state: PossiblyConditionalState.Create(this), believedReachable: true));
 
  var labelStateMap = PooledDictionary<LabelSymbol, (LocalState state, bool believedReachable)>.GetInstance();
 
@@ -735,8 +732,7 @@ private void VisitSwitchExpressionCore(BoundSwitchExpression node, bool inferTyp
 
  Visit(node.Expression);
  var expressionState = ResultType;
- var state = PossiblyConditionalState.Create(this);
- var labelStateMap = LearnFromDecisionDag(node.Syntax, node.DecisionDag, node.Expression, expressionState, ref state);
+ var labelStateMap = LearnFromDecisionDag(node.Syntax, node.DecisionDag, node.Expression, expressionState);
  var endState = UnreachableState();
 
  if (!node.ReportedNotExhaustive && node.DefaultLabel != null &&
@@ -846,8 +842,7 @@ public override BoundNode VisitIsPatternExpression(BoundIsPatternExpression node
  VisitPatternForRewriting(node.Pattern);
  Visit(node.Expression);
  var expressionState = ResultType;
- var state = PossiblyConditionalState.Create(this);
- var labelStateMap = LearnFromDecisionDag(node.Syntax, node.DecisionDag, node.Expression, expressionState, ref state);
+ var labelStateMap = LearnFromDecisionDag(node.Syntax, node.DecisionDag, node.Expression, expressionState);
  var trueState = labelStateMap.TryGetValue(node.IsNegated ? node.WhenFalseLabel : node.WhenTrueLabel, out var s1) ? s1.state : UnreachableState();
  var falseState = labelStateMap.TryGetValue(node.IsNegated ? node.WhenTrueLabel : node.WhenFalseLabel, out var s2) ? s2.state : UnreachableState();
  labelStateMap.Free();

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

@@ -87,7 +87,7 @@ public TypeWithAnnotations ToTypeWithAnnotations(CSharpCompilation compilation,
  if (Type?.IsTypeParameterDisallowingAnnotationInCSharp8() == true)
  {
  var type = TypeWithAnnotations.Create(Type, NullableAnnotation.NotAnnotated);
- return State == NullableFlowState.MaybeDefault ? type.SetIsAnnotated(compilation) : type;
+ return (State == NullableFlowState.MaybeDefault || asAnnotatedType) ? type.SetIsAnnotated(compilation) : type;
  }
  NullableAnnotation annotation = asAnnotatedType ?
  (Type?.IsValueType == true ? NullableAnnotation.NotAnnotated : NullableAnnotation.Annotated) :

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

@@ -5112,9 +5112,10 @@ void M<T>(T t)
  var declaration = syntaxTree.GetRoot().DescendantNodes().OfType<VariableDeclaratorSyntax>().Single();
  var model = comp.GetSemanticModel(syntaxTree);
  var local = (ILocalSymbol)model.GetDeclaredSymbol(declaration);
- Assert.Equal(CodeAnalysis.NullableAnnotation.NotAnnotated, local.NullableAnnotation);
- Assert.Equal(CodeAnalysis.NullableAnnotation.NotAnnotated, local.Type.NullableAnnotation);
- Assert.Equal("T", local.Type.ToTestDisplayString(includeNonNullable: true));
+ Assert.Equal("T? t2", local.ToTestDisplayString());
+ Assert.Equal(CodeAnalysis.NullableAnnotation.Annotated, local.NullableAnnotation);
+ Assert.Equal(CodeAnalysis.NullableAnnotation.Annotated, local.Type.NullableAnnotation);
+ Assert.Equal("T?", local.Type.ToTestDisplayString(includeNonNullable: true));
  }
 
  [Fact]
@@ -142889,30 +142890,18 @@ static T F5<T, U>(U x5) where U : T?
 }";
  var comp = CreateCompilation(source, parseOptions: TestOptions.Regular9);
  comp.VerifyDiagnostics(
- // (7,14): warning CS8600: Converting null literal or possible null value to non-nullable type.
- // y1 = default(T);
- Diagnostic(ErrorCode.WRN_ConvertingNullableToNonNullable, "default(T)").WithLocation(7, 14),
  // (8,16): warning CS8603: Possible null reference return.
  // return y1; // 1
  Diagnostic(ErrorCode.WRN_NullReferenceReturn, "y1").WithLocation(8, 16),
  // (14,16): warning CS8603: Possible null reference return.
  // return y2; // 2
  Diagnostic(ErrorCode.WRN_NullReferenceReturn, "y2").WithLocation(14, 16),
- // (19,14): warning CS8600: Converting null literal or possible null value to non-nullable type.
- // y3 = default(T);
- Diagnostic(ErrorCode.WRN_ConvertingNullableToNonNullable, "default(T)").WithLocation(19, 14),
  // (20,16): warning CS8603: Possible null reference return.
  // return y3; // 3
  Diagnostic(ErrorCode.WRN_NullReferenceReturn, "y3").WithLocation(20, 16),
- // (25,14): warning CS8600: Converting null literal or possible null value to non-nullable type.
- // y4 = default(T);
- Diagnostic(ErrorCode.WRN_ConvertingNullableToNonNullable, "default(T)").WithLocation(25, 14),
  // (26,16): warning CS8603: Possible null reference return.
  // return y4; // 4
  Diagnostic(ErrorCode.WRN_NullReferenceReturn, "y4").WithLocation(26, 16),
- // (31,14): warning CS8600: Converting null literal or possible null value to non-nullable type.
- // y5 = default(U);
- Diagnostic(ErrorCode.WRN_ConvertingNullableToNonNullable, "default(U)").WithLocation(31, 14),
  // (32,16): warning CS8603: Possible null reference return.
  // return y5; // 5
  Diagnostic(ErrorCode.WRN_NullReferenceReturn, "y5").WithLocation(32, 16));
@@ -142922,11 +142911,11 @@ static T F5<T, U>(U x5) where U : T?
  var locals = tree.GetRoot().DescendantNodes().OfType<VariableDeclaratorSyntax>().ToArray();
  Assert.Equal(5, locals.Length);
  // https://github.com/dotnet/roslyn/issues/46236: Locals should be treated as annotated.
- VerifyVariableAnnotation(model, locals[0], "T y1", NullableAnnotation.NotAnnotated);
+ VerifyVariableAnnotation(model, locals[0], "T? y1", NullableAnnotation.Annotated);
  VerifyVariableAnnotation(model, locals[1], "T? y2", NullableAnnotation.Annotated);
- VerifyVariableAnnotation(model, locals[2], "T y3", NullableAnnotation.NotAnnotated);
- VerifyVariableAnnotation(model, locals[3], "T y4", NullableAnnotation.NotAnnotated);
- VerifyVariableAnnotation(model, locals[4], "U y5", NullableAnnotation.NotAnnotated);
+ VerifyVariableAnnotation(model, locals[2], "T? y3", NullableAnnotation.Annotated);
+ VerifyVariableAnnotation(model, locals[3], "T? y4", NullableAnnotation.Annotated);
+ VerifyVariableAnnotation(model, locals[4], "U? y5", NullableAnnotation.Annotated);
  }
 
  private static void VerifyVariableAnnotation(SemanticModel model, VariableDeclaratorSyntax syntax, string expectedDisplay, NullableAnnotation expectedAnnotation)
@@ -146719,5 +146708,143 @@ void M(I3 i)
  AssertEx.Equal(new string[] { "I<object?>", "I2<object!>", "I<object!>" },
  i3.AllInterfaces().ToTestDisplayStrings(TypeWithAnnotations.TestDisplayFormat));
  }
+
+ [Fact]
+ public void VarPatternDeclaration_TopLevel()
+ {
+ var src = @"
+#nullable enable
+public class C
+{
+ public void M(string? x)
+ {
+ if (Identity(x) is var y)
+ {
+ y.ToString(); // 1
+ }
+
+ if (Identity(x) is not null and var z)
+ {
+ z.ToString();
+ }
+ }
+
+ public T Identity<T>(T t) => t;
+}
+";
+ var comp = CreateCompilation(src);
+ comp.VerifyDiagnostics(
+ // (9,13): warning CS8602: Dereference of a possibly null reference.
+ // y.ToString(); // 1
+ Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "y").WithLocation(9, 13)
+ );
+ }
+
+ [Fact]
+ public void VarPatternDeclaration_Nested()
+ {
+ var src = @"
+#nullable enable
+public class Container<T>
+{
+ public T Item { get; set; } = default!;
+}
+public class C
+{
+ public void M(Container<string?> x)
+ {
+ if (Identity(x) is { Item: var y })
+ {
+ y.ToString(); // 1
+ }
+
+ if (Identity(x) is { Item: not null and var z })
+ {
+ z.ToString();
+ }
+ }
+
+ public T Identity<T>(T t) => t;
+}
+";
+ var comp = CreateCompilation(src);
+ comp.VerifyDiagnostics(
+ // (13,13): warning CS8602: Dereference of a possibly null reference.
+ // y.ToString(); // 1
+ Diagnostic(ErrorCode.WRN_NullReferenceReceiver, "y").WithLocation(13, 13)
+ );
+ }
+
+ [Theory, WorkItem(52925, "https://github.com/dotnet/roslyn/issues/52925")]
+ [WorkItem(46236, "https://github.com/dotnet/roslyn/issues/46236")]
+ [InlineData("")]
+ [InlineData(" where T : notnull")]
+ [InlineData(" where T : class")]
+ [InlineData(" where T : class?")]
+ public void VarDeclarationWithGenericType(string constraint)
+ {
+ var src = $@"
+#nullable enable
+
+class C<T> {constraint}
+{{
+ void M(T initial, System.Func<T, T?> selector)
+ {{
+ for (var current = initial; current != null; current = selector(current))
+ {{
+ }}
+
+ var current2 = initial;
+ current2 = default;
+
+ for (T? current3 = initial; current3 != null; current3 = selector(current3))
+ {{
+ }}
+
+ T? current4 = initial;
+ current4 = default;
+ }}
+}}
+";
+ var comp = CreateCompilation(src);
+ comp.VerifyDiagnostics();
+
+ var tree = comp.SyntaxTrees.Single();
+ var model = comp.GetSemanticModel(tree, ignoreAccessibility: false);
+ var declarations = tree.GetRoot().DescendantNodes().OfType<VariableDeclarationSyntax>();
+ foreach (var declaration in declarations)
+ {
+ var local = (ILocalSymbol)model.GetDeclaredSymbol(declaration.Variables.Single());
+ Assert.Equal("T?", local.Type.ToTestDisplayString());
+ Assert.Equal(CodeAnalysis.NullableAnnotation.Annotated, local.Type.NullableAnnotation);
+ }
+ }
+
+ [Theory, WorkItem(52925, "https://github.com/dotnet/roslyn/issues/52925")]
+ [InlineData("")]
+ [InlineData(" where T : notnull")]
+ [InlineData(" where T : class")]
+ [InlineData(" where T : class?")]
+ public void VarDeclarationWithGenericType_RefValue(string constraint)
+ {
+ var src = $@"
+#nullable enable
+
+class C<T> {constraint}
+{{
+ ref T Passthrough(ref T value)
+ {{
+ ref var value2 = ref value;
+ return ref value2;
+ }}
+}}
+";
+ var comp = CreateCompilation(src);
+ comp.VerifyDiagnostics(
+ // (9,20): warning CS8619: Nullability of reference types in value of type 'T?' doesn't match target type 'T'.
+ // return ref value2;
+ Diagnostic(ErrorCode.WRN_NullabilityMismatchInAssignment, "value2").WithArguments("T?", "T").WithLocation(9, 20)
+ );
+ }
  }
 }

src/Dependencies/Collections/SegmentedDictionary`2.cs

@@ -442,7 +442,7 @@ private ref TValue FindValue(TKey key)
 ConcurrentOperation:
  ThrowHelper.ThrowInvalidOperationException_ConcurrentOperationsNotSupported();
 ReturnFound:
- ref var value = ref entry._value;
+ ref TValue value = ref entry._value;
 Return:
  return ref value;
 ReturnNotFound: