Bug 517028

Summary: Strange LINQ Expression behaviour
Product: [Mono] Mono: Class Libraries Reporter: Federico Di Gregorio <fog>
Component: Sys.CoreAssignee: Michael Miller <michael.miller>
Status: NEW --- QA Contact: Mono Bugs <mono-bugs>
Severity: Normal    
Priority: P5 - None    
Version: SVN   
Target Milestone: 2.4.x   
Hardware: x86-64   
OS: Linux   
Whiteboard:
Found By: --- Services Priority:
Business Priority: Blocker: ---
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Description Federico Di Gregorio 2009-06-26 20:26:45 UTC 
The simple code that follows shows two different problems detailed below.

using System;
using System.Linq.Expressions;

class Test
{
    public static void Main()
    {
        int? i = 0;
        Expression<Func<String>> e3 = Expression.Lambda<Func<String>>(
            Expression.Convert(Expression.Constant(i), typeof(String),
                               typeof(Convert).GetMethod("ToString", new Type[1] { typeof(int?) })));
        Console.WriteLine("SHOULD NOT WHIS BE NULL? " + typeof(Convert).GetMethod("ToString", new Type[1] { typeof(int?) }));
        Console.WriteLine(e3.Compile()());
    }
}

Problems:

While Convert does not have a ToString(Int32?) method, GetMethod returns a method with ToString(Object) as signature instead of null.

The program fails during Compile() with a "System.InvalidProgramException: Invalid IL code" exception.
Comment 1 Miguel de Icaza 2009-06-26 20:29:38 UTC 
The problem is that our LINQ implementation should throw an exception because there is a parameter mismatch.

.NET reports:

InvalidOperationException: The operatnds for operator 'Convert' do not match the parameter of method 'ToString'.

We instead silently compile incorrect code