谓词成员引用

Question

编译器将LINQ函数谓词转换为名称为"Predicate`1“的FieldInfo。我想分析这些FieldInfo，看看有哪些成员被引用。例如，下面的谓词使用用户定义的方法"ArchName"：

list.FindAll(m => !m.ArchName().Contains("<>c"))

我不知道FieldInfo有任何相关的MethodInfo成员。可以做些什么呢？

提前感谢！

Answer 1

这与LINQ无关。它是纯粹的C#λ表达式+列表。

在本例中为Predicate 1is not a *field name*, but instead, a type, more preciselySystem.Predicate`。

在我看来，您希望分析方法体以查找对此类型的引用。即使这可能是通过反射来实现的，您也可以使用Mono.Cecil；在这种情况下，您可以使用如下内容(请注意，这段代码并不是以任何方式都不完整...您需要考虑错误、静态字段等)：

using System.Collections.Generic;
using System.Linq;
using Mono.Cecil;
using Mono.Cecil.Cil;

class Bar
{
    void Foo(List<int> items)
    {
        // A non sense expression :)
        var r = items.FindAll(i => i % 2 == 0 || i.ToString() == "A");
    }

    static void Main()
    {
        var a = AssemblyDefinition.ReadAssembly(typeof(Bar).Assembly.Location);

        var allMethods = a.MainModule.GetTypes().SelectMany(t => t.Methods);

        // find instructions referencing System.Predicate<T>
        var allMethodsReferencingSystemPredicate = allMethods.Where(m => m.Body.Instructions.Any(i => i.OpCode == OpCodes.Newobj && i.Operand.ToString().Contains("System.Predicate`1")));
        foreach(var m in allMethodsReferencingSystemPredicate)
        {
            System.Console.WriteLine($"Analyzing {m}");
            
            var instReferencingSystemPredicate = m.Body.Instructions.Where(i => i.OpCode == OpCodes.Newobj && i.Operand.ToString().Contains("System.Predicate`1"));            
            foreach(var inst in instReferencingSystemPredicate)
            {
                System.Console.WriteLine($"Checking {inst} / {inst.Previous}");
                if (inst.Previous.OpCode != OpCodes.Ldftn)
                {
                    System.Console.WriteLine($"Something went wrong. Expected LdFnt, got {inst.Previous.OpCode} in instruction {inst.Previous}");
                    continue;
                }
                // get the method being referenced.
                var method = ((MethodReference) inst.Previous.Operand).Resolve();
                
                // Analyze the method body looking for calls to `ToString()` (you will replace this with your own checks...)
                foreach(var methodInst in method.Body.Instructions)
                {
                    //System.Console.WriteLine($"Checking: {methodInst}");
                    if ( (methodInst.OpCode == OpCodes.Callvirt || methodInst.OpCode == OpCodes.Call) && methodInst.Operand.ToString().Contains("ToString()"))
                    {
                        System.Console.BackgroundColor = System.ConsoleColor.DarkCyan;
                        System.Console.WriteLine($"{method} (used in {m}) references ToString(): {methodInst}");
                    } 
                }
            }
        }

    }
}