List-patterns: symbols not correctly updated with nullability information

[jcouv]

This will likely be fixed as side-effect of pulling Receiver out of IndexerAccess (issue #57855)

        [CompilerTrait(CompilerFeature.IOperation)]
        [Fact]
        public void TestIsPatternExpression_ListPatterns_Collection_Nullability()
        {
            string source = @"
#nullable enable
class X<T>
{
    static X<U> Create<U>(U u) => throw null!;
    void M(string s)
    {
        s = null;
        var a = Create(s);
        _ = /*<bind>*/a is [var item]/*</bind>*/;
    }
    public int Length => throw null!;
    public char this[int i] => throw null!;
}
";
            // The LengthSymbol and IndexerSymbol should reflect updated nullability:
            // LengthSymbol: System.Int32 X<System.String?>.Length { get; }, IndexerSymbol: System.Char X<System.String?>.this[System.Int32 i] { get; })
            string expectedOperationTree = @"
IIsPatternOperation (OperationKind.IsPattern, Type: System.Boolean) (Syntax: 'a is [var item]')
  Value:
    ILocalReferenceOperation: a (OperationKind.LocalReference, Type: X<System.String?>) (Syntax: 'a')
  Pattern:
    IListPatternOperation (OperationKind.ListPattern, Type: null) (Syntax: '[var item]') (InputType: X<System.String>, NarrowedType: X<System.String>, DeclaredSymbol: null, LengthSymbol: System.Int32 X<System.String>.Length { get; }, IndexerSymbol: System.Char X<System.String>.this[System.Int32 i] { get; })
      Patterns (1):
          IDeclarationPatternOperation (OperationKind.DeclarationPattern, Type: null) (Syntax: 'var item') (InputType: System.Char, NarrowedType: System.Char, DeclaredSymbol: System.Char item, MatchesNull: True)
";
            var expectedDiagnostics = new[]
            {
                // (8,13): warning CS8600: Converting null literal or possible null value to non-nullable type.
                //         s = null;
                Diagnostic(ErrorCode.WRN_ConvertingNullableToNonNullable, "null").WithLocation(8, 13)
            };

            var comp = CreateCompilationWithIndexAndRange(new[] { source, TestSources.GetSubArray });
            VerifyOperationTreeAndDiagnosticsForTest<IsPatternExpressionSyntax>(comp, expectedOperationTree, expectedDiagnostics);
        }

[AlekseyTs]

It looks like this issue is not specific to list patterns. For example, nullability of symbols for property sub-patterns isn't updated as well:

        [CompilerTrait(CompilerFeature.IOperation)]
        [Fact]
        public void Test()
        {
            string source = @"
#nullable enable
class X<T>
{
    static X<U> Create<U>(U u) => throw null!;
    void M(string s)
    {
        s = null;
        var a = Create(s);
        _ = /*<bind>*/a is { Length: 1 }/*</bind>*/;
    }
    public int Length => throw null!;
    public char this[int i] => throw null!;
}
";
            string expectedOperationTree = @"
IIsPatternOperation (OperationKind.IsPattern, Type: System.Boolean) (Syntax: 'a is { Length: 1 }')
  Value:
    ILocalReferenceOperation: a (OperationKind.LocalReference, Type: X<System.String?>) (Syntax: 'a')
  Pattern:
    IRecursivePatternOperation (OperationKind.RecursivePattern, Type: null) (Syntax: '{ Length: 1 }') (InputType: X<System.String>, NarrowedType: X<System.String>, DeclaredSymbol: null, MatchedType: X<System.String>, DeconstructSymbol: null)
      DeconstructionSubpatterns (0)
      PropertySubpatterns (1):
          IPropertySubpatternOperation (OperationKind.PropertySubpattern, Type: null) (Syntax: 'Length: 1')
            Member:
              IPropertyReferenceOperation: System.Int32 X<System.String>.Length { get; } (OperationKind.PropertyReference, Type: System.Int32) (Syntax: 'Length')
                Instance Receiver:
                  IInstanceReferenceOperation (ReferenceKind: PatternInput) (OperationKind.InstanceReference, Type: X<System.String>, IsImplicit) (Syntax: 'Length')
            Pattern:
              IConstantPatternOperation (OperationKind.ConstantPattern, Type: null) (Syntax: '1') (InputType: System.Int32, NarrowedType: System.Int32)
                Value:
                  ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
";
            var expectedDiagnostics = new[]
            {
                // (8,13): warning CS8600: Converting null literal or possible null value to non-nullable type.
                //         s = null;
                Diagnostic(ErrorCode.WRN_ConvertingNullableToNonNullable, "null").WithLocation(8, 13)
            };

            var comp = CreateCompilation(source);
            VerifyOperationTreeAndDiagnosticsForTest<IsPatternExpressionSyntax>(comp, expectedOperationTree, expectedDiagnostics);
        }

[AlekseyTs]

CC @333fred