[nem-bug] [Nemerle 0000701]: [0.9.3] Empty structs have $PLACE_HOLDER$ field

[feedback at nemerle.org]

The following issue has been REOPENED.
======================================================================
<http://nemerle.org/bugs/view.php?id=701> 
======================================================================
Reported By:                Snaury
Assigned To:                nazgul
======================================================================
Project:                    Nemerle
Issue ID:                   701
Category:                   Compiler
Reproducibility:            always
Severity:                   feature
Priority:                   normal
Status:                     feedback
======================================================================
Date Submitted:             07-01-2006 16:05 CEST
Last Modified:              07-02-2006 15:28 CEST
======================================================================
Summary:                    [0.9.3] Empty structs have $PLACE_HOLDER$ field
Description: 
The following code:

  public struct EmptyStruct { }

produces empty structure with the following IL:

.class public sequential ansi sealed beforefieldinit EmptyStruct
       extends [mscorlib]System.ValueType
{
  .pack 0
  .size 1
} // end of class EmptyStruct

Nemerle's generated structure has no the following IL:

.class public auto ansi sealed EmptyStruct
       extends [mscorlib]System.ValueType
{
  .field private specialname uint8 $PLACE_HOLDER$
} // end of class EmptyStruct


As you can see, they differ and Nemerle's IL has strange $PLACE_HOLDER$
field. If possible, it would be good if generated code would be without
this $PLACE_HOLDER$ field...
======================================================================

----------------------------------------------------------------------
 nazgul - 07-01-06 21:26 
----------------------------------------------------------------------
AFAIR as added this field to mimick the C# compiler. But maybe has changed
after .NET 1.1 or it was mono compiler's behaviour. It must be checked if
this is still needed.

----------------------------------------------------------------------
 nazgul - 07-02-06 12:56 
----------------------------------------------------------------------
After using a patch I get verification error for empty structs:

bash-3.00$ ../../tools/verify out.exe 

Microsoft (R) .NET Framework PE Verifier.  Version  2.0.50727.42
Copyright (c) Microsoft Corporation.  All rights reserved.

[MD]: Error: ClassLayout has parent TypeDef token=0x02000002 marked
AutoLayout. [token:0x00000001]
1 Error Verifying out.exe


I'm investigating the possible fix.

----------------------------------------------------------------------
 Snaury - 07-02-06 13:11 
----------------------------------------------------------------------
Seems like after that class needs to be marked Sequential. I don't yet know
how type lookup in compiler works, though, so I don't know how a
StructLayout custom attribute can be applied on that struct...

----------------------------------------------------------------------
 nazgul - 07-02-06 13:15 
----------------------------------------------------------------------
At the stage of emitting hierarchy by S.R.E we can just define this
attribute using  code similar to make_nemerle_variant_attribute  in
HierarchyEmitter.n

----------------------------------------------------------------------
 nazgul - 07-02-06 13:46 
----------------------------------------------------------------------
I enchanced the patch and commited it, thanks!

Fixed on trunk (r6416).

----------------------------------------------------------------------
 Snaury - 07-02-06 15:28 
----------------------------------------------------------------------
Unless it's not too late, by occasion I found that you don't need to apply
attribute to achieve sequential layout, plus I found that both mcs and c#
default to sequential layout for structs (which can later be overriden by
applying attribute in user code). Besides, I found a way to better mimick
mcs behaviour, in regard for example to beforefieldinit flag (set
beforefieldinit when there is no static constructor). I'll attach new
patch against r6417.

Issue History
Date Modified  Username       Field                    Change              
======================================================================
07-01-06 16:05 Snaury         New Issue                                    
07-01-06 20:30 Snaury         File Added: bug-placeholder.patch                 
  
07-01-06 21:26 nazgul         Note Added: 0001331                          
07-02-06 12:56 nazgul         Note Added: 0001334                          
07-02-06 13:11 Snaury         Note Added: 0001335                          
07-02-06 13:15 nazgul         Note Added: 0001336                          
07-02-06 13:46 nazgul         Status                   new => resolved     
07-02-06 13:46 nazgul         Resolution               open => fixed       
07-02-06 13:46 nazgul         Assigned To               => nazgul          
07-02-06 13:46 nazgul         Note Added: 0001337                          
07-02-06 13:46 nazgul         Description Updated                          
07-02-06 15:28 Snaury         Status                   resolved => feedback
07-02-06 15:28 Snaury         Resolution               fixed => reopened   
07-02-06 15:28 Snaury         Note Added: 0001340                          
======================================================================