[Mono-bugs] [Bug 420832] New: [GMCS] Regression from 1.9, unexpected NullException thrown when creating new lists, from empty lists and yield returns.

[bugzilla_noreply at novell.com]

https://bugzilla.novell.com/show_bug.cgi?id=420832


           Summary: [GMCS] Regression from 1.9, unexpected NullException
                    thrown when creating new lists, from empty lists and
                    yield returns.
           Product: Mono: Compilers
           Version: 2.0
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: Vernish13 at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---


The following bug is present in the Mono 2.0 branch and mono trunk.  The bug is
NOT present in mono 1.9.

An unexpected NullReferenceException is thrown when creating a new List<T>
twice from an empty IEnumerable<T> that was returned from another class and
used yield return.

This example works correctly using mono & csc assemblies.  gmcs assemblies with
NET runtime will produce the bug.

Bug Output : 

Unhandled Exception: System.NullReferenceException: Object reference not set to
an instance of an object
  at MySystem+<>c__Iterator0.MoveNext () [0x00000]
  at System.Collections.Generic.List`1[System.Object].AddEnumerable
(IEnumerable`1 enumerable) [0x00000]
  at System.Collections.Generic.List`1[System.Object]..ctor (IEnumerable`1
collection) [0x00000]
  at Test.findNearestSource (IEnumerable`1 items) [0x00000]
  at Test.Main (System.String[] args) [0x00000]

Correct Output : 

[TEST] Done

Code : 

using System;
using System.Collections.Generic;

public class Test
{
    public static void Main(String[] args)
    {
        MySystem mySystem = new MySystem();

        TestFunction(mySystem.Items);

        Console.WriteLine("[TEST] Done");
    }

    public static void TestFunction(IEnumerable<string> items)
    {
        List<string> newList;
        newList = new List<string>(items);
        newList = new List<string>(items);
    }
}

public class MySystem
{
    private List<string> _items = new List<string>();

    public MySystem()
    {
    }

    public IEnumerable<string> Items
    {
        get
        {
            foreach (string i in _items)
            {
                yield return i;
            }
        }
    }
}


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