C# compiler bug? Object initializer syntax used for write-only property in Expression makes csc crash

Question

You may consider this a bug report, however I'm curious if I am terribly wrong here, or if there is an explanation from Eric or someone else at Microsoft.

Update

This is now posted as a bug on Microsoft Connect.

Description

Consider the following class:

class A 
{
    public object B {
        set { }
    }
}

Here, A.B is a write-only but otherwise fine property.
Now, imagine we assign it inside of expression:

Expression<Func<A>> expr = 
    () => new A {
        B = new object { }
    };

This code makes C# compiler (both 3.5.30729.4926 and 4.0.30319.1) spit out

Internal Compiler Error (0xc0000005 at address 013E213F): likely culprit is 'BIND'.

and crash.

However, merely replacing object initializer syntax ({ }) with a constructor (( )) compiles just fine.

Full code for reproduction:

using System;
using System.Linq.Expressions;

class Test {
    public static void Main()
    {
        Expression<Func<A>> expr = 
            () => new A {
                B = new object { }
            };
    }
}

class A {
    public object B { set { } }
}

(And yes, I did hit it working on a real project.)

Answer 1

I'm afraid I'm not Eric Lippert (Oh, but could I be so dashing...), but as a former Visual Studio languages guy who can still search the sources, I can say two things about this:

1. Any time you see something that starts with "Internal Compiler Error" you have most definitely found a bug. That's what that error exists for, whether it's the C#, VB or C++ compiler. It's the "Oh, s**t, something just went really unexpectedly wrong!" throw-up-our-hands-and-bail-out error.

2. Beyond that, this is definitely a bug in the C# compiler that should be reported. The code that's crashing is assuming that when you're doing an initializer on a property that there's a getter it can look at and, hey, guess what? In this case, there isn't. Oddly enough, if I change the type being constructed to some type "C" instead of "object", I don't get the crash, so I'm guessing it's a failure further up the stack (i.e. the code never should have gotten down to the point where it was looking for the property getter).

Hope this helps.

Answer 2

This is what I found online related to the error,

Posted by Microsoft on 3/9/2010 at 10:58 AM

Thanks everyone for the reports. I believe that this issue has been fixed post-RC. The problem is that the C# compiler is crashing as it is tries to report an error or warning. In several cases we have seen the warning being reported is that the LIB environment variable contains an invalid path. To avoid the crash, check that your LIB environment variable contains valid paths.

Regards,

Ed Maurer Development Manager, VB and C# compilers