IOperation support for implicit Index/Range indexer over non-array types

[AlekseyTs]

    /// <summary>
    /// Represents a reference to an implicit Index or Range indexer over non-array type.
    /// <para>
    /// Current usage:
    ///  (1) C# implicit Index or Range indexer reference expression.
    /// </para>
    /// </summary>
    /// <remarks>
    /// <para>This node is associated with the following operation kinds:</para>
    /// <list type="bullet">
    /// <item><description><see cref="OperationKind.ImplicitIndexerReference"/></description></item>
    /// </list>
    /// <para>This interface is reserved for implementation by its associated APIs. We reserve the right to
    /// change it in the future.</para>
    /// </remarks>
    public interface IImplicitIndexerReferenceOperation : IOperation
    {
        /// <summary>
        /// Instance of the type to be indexed.
        /// </summary>
        IOperation Instance { get; }

        /// <summary>
        /// Index or Range value.
        /// </summary>
        IOperation Index { get; }

        /// <summary>
        /// The <c>Length</c> or <c>Count</c> property that can be used to fetch the length value.
        /// </summary>
        ISymbol LengthSymbol { get; }

        /// <summary>
        /// Symbol for the underlying indexer or a slice method that is being used to implement the implicit indexer.
        /// </summary>
        ISymbol IndexerSymbol { get; }
    }

Implicit Index/Range indexer over array types will continue to be represented as IArrayElementReferenceOperation.

See also proposal for list patterns #57194.

[333fred]

API Review

• Naming: we have both Reference and Access in existing names
  • We'll keep it as is to keep in line IPropertyReferenceOperation
• We'll rename Index to Argument to line up with IPropertyReferenceOperation

Conclusion

Rename Index to Argument. Otherwise, API is approved.

[alrz]

/// <summary>
/// Symbol for the underlying indexer or a slice method that is being used to implement the implicit indexer.
/// </summary>
ISymbol IndexerSymbol { get; }

With this addition, shouldn't we use IndexerSymbol for ISlicePatternOperation.SliceSymbol as well? (that's unshipped afaik)

[AlekseyTs]

With this addition, shouldn't we use IndexerSymbol for ISlicePatternOperation.SliceSymbol as well? (that's unshipped afaik)

As far as I understand the ISlicePatternOperation.SliceSymbol is always used to slice. Even if it is an indexer, it must take Range. An indexer returned by IImplicitIndexerReferenceOperation.IndexerSymbol is always used to index. It must take int. The name ISlicePatternOperation.SliceSymbol looks Ok to me.