110 lines
4.3 KiB
C#
110 lines
4.3 KiB
C#
// Copyright (c) .NET Foundation. All rights reserved.
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// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
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using System;
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using System.Collections.Concurrent;
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using System.Collections.Generic;
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using System.Linq.Expressions;
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using Microsoft.Extensions.Internal;
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namespace Microsoft.AspNetCore.Mvc.ViewFeatures.Internal
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{
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/// <summary>
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/// This class holds the cache for the expression text that is computed by ExpressionHelper.
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/// </summary>
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public class ExpressionTextCache
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{
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/// <inheritdoc />
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public ConcurrentDictionary<LambdaExpression, string> Entries { get; } =
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new ConcurrentDictionary<LambdaExpression, string>(LambdaExpressionComparer.Instance);
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// This comparer is tightly coupled with the logic of ExpressionHelper.GetExpressionText.
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// It is not designed to accurately compare any two arbitrary LambdaExpressions.
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private class LambdaExpressionComparer : IEqualityComparer<LambdaExpression>
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{
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public static readonly LambdaExpressionComparer Instance = new LambdaExpressionComparer();
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public bool Equals(LambdaExpression lambdaExpression1, LambdaExpression lambdaExpression2)
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{
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if (ReferenceEquals(lambdaExpression1,lambdaExpression2))
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{
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return true;
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}
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// We will cache only pure member access expressions. Hence we compare two expressions
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// to be equal only if they are identical member access expressions.
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var expression1 = lambdaExpression1.Body;
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var expression2 = lambdaExpression2.Body;
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while (true)
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{
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if (expression1 == null || expression2 == null)
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{
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return false;
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}
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if (expression1.NodeType != expression2.NodeType)
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{
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return false;
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}
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if (expression1.NodeType == ExpressionType.MemberAccess)
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{
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var memberExpression1 = (MemberExpression)expression1;
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var memberName1 = memberExpression1.Member.Name;
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expression1 = memberExpression1.Expression;
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var memberExpression2 = (MemberExpression)expression2;
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var memberName2 = memberExpression2.Member.Name;
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expression2 = memberExpression2.Expression;
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// If identifier contains "__", it is "reserved for use by the implementation" and likely compiler-
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// or Razor-generated e.g. the name of a field in a delegate's generated class.
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if (memberName1.Contains("__") && memberName2.Contains("__"))
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{
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return true;
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}
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if (!string.Equals(memberName1, memberName2, StringComparison.OrdinalIgnoreCase))
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{
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return false;
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}
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}
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else
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{
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return true;
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}
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}
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}
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public int GetHashCode(LambdaExpression lambdaExpression)
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{
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var expression = lambdaExpression.Body;
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var hashCodeCombiner = HashCodeCombiner.Start();
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while (true)
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{
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if (expression != null && expression.NodeType == ExpressionType.MemberAccess)
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{
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var memberExpression = (MemberExpression)expression;
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var memberName = memberExpression.Member.Name;
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if (memberName.Contains("__"))
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{
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break;
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}
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hashCodeCombiner.Add(memberName, StringComparer.OrdinalIgnoreCase);
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expression = memberExpression.Expression;
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}
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else
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{
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break;
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}
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}
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return hashCodeCombiner.CombinedHash;
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}
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}
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}
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}
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