// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using System;

namespace Microsoft.CodeAnalysis.CSharp.Debugging;

internal sealed partial class CSharpProximityExpressionsService
{
    // Flags used for "collecting" terms for proximity expressions.  The flags are somewhat
    // confusing.  The key point to remember is that an expression will be placed in the result
    // set if and only if ValidTerm is set.  ValidExpression is used to indicate that while an
    // expression may not be a ValidTerm by itself, it can be used as a sub-expression of a
    // larger expression that IS a ValidTerm.  (Note: ValidTerm implies ValidExpression)
    //
    // For example, consider the expression a[b+c].  The analysis of this expression starts at
    // the ElementAccessExpression.  The rules for an ElementAccessExpression say that the
    // expression is a ValidTerm if and only if both the LHS('a' in this case) and the
    // RHS('b+c') are valid ValidExpressions. The LHS is a ValidTerm, and the RHS is a binary
    // operator-- this time AddExpression. The rules for AddExpression state that the expression
    // is never a ValidTerm, but is a ValidExpression if both the LHS and the RHS are
    // ValidExpressions. In this case, both 'b' and 'c' are ValidTerms (thus valid expressions),
    // so 'a+b' is a ValidExpression (but not a ValidTerm), and finally 'a[b+c]' is considered a
    // ValidTerm. So, the result of GetProximityExpressions for this expression would be:
    //
    // a
    //
    // b
    //
    // c
    //
    // a[b+c]
    //
    // (but not "b+c")
    [Flags]
    private enum ExpressionType
    {
        Invalid = 0x0,
        ValidExpression = 0x1,

        // Note: ValidTerm implies ValidExpression.
        ValidTerm = 0x3
    }
}