[nem-bug] [Nemerle 0000625]: strange error when misusing macro-generated type

[feedback at nemerle.org]

The following issue has been RESOLVED.
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<http://nemerle.org/bugs/view.php?id=625> 
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Reported By:                aleksey
Assigned To:                nazgul
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Project:                    Nemerle
Issue ID:                   625
Category:                   Compiler
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     resolved
Resolution:                 fixed
Fixed in Version:           
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Date Submitted:             02-22-2006 10:40 CET
Last Modified:              05-01-2006 12:50 CEST
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Summary:                    strange error when misusing macro-generated type
Description: 
When someone misuses(e.g. uses non-existent function or property accessor)
a type defined from macro, he gets a quite strange error message.

E.g. lets suppose we have a macro 'define', which defines type with a
supplied name, etc.

define(Test);
def t = Test(1);
// there is no 'Prop' property in Test
System.Console.WriteLine(t.Prop);

The following error message is displayed:
c.n:1:1:1:7: you must specify `partial' modifier on all declarations of
type `Test'
c.n:1:1:1:7: first defined here
c.n:1:1:1:7: field `Test.test' redefined in `Test'
c.n:1:1:1:7: first definition here as field `Test.test'
confused by earlier errors bailing out
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----------------------------------------------------------------------
 nazgul - 02-22-06 11:13 
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Looks like the type is added twice to the compilation tree. I'm not sury
why though. Did you check the examples from
ncc/testsuite/positive/macrolib.n and macroprog.n?

----------------------------------------------------------------------
 aleksey - 02-22-06 12:51 
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Here's how to reproduce this error via macro from macrolib.n:

def x = generateIFoo();
_ = x.Test;

----------------------------------------------------------------------
 steffen - 02-22-06 15:20 
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The problem is that the macro is called twice when an error occurs:

macrolib.n:
macro M () {
    System.Console.WriteLine ("Macro called");
    Nemerle.Macros.ImplicitCTX ().Env.Define
    (<[ decl:
       public class BlahBle { }
       ]>).Compile ();
    <[ () ]>
}


If you compile the code:
M();
the compiler will output:
Macro called
and the compilation will work.


If you, however, try to compile
M();
asdf();
the compiler will output:
Macro called
Macro called
test.n:1:1:1:2: error: you must specify `partial' modifier on all
declarations of type `BlahBle'
test.n:1:1:1:2: error: first defined here
confused by earlier errors bailing out

I don't know exactly why the compiler evaluates the macro twice in case of
an error. (He seems to restart in some error mode.) This behaviour doesn't
matter as long as the macro is pure functional (which in most cases is
true).

However, to solve this problem you either have to check, that the type is
created only once, even when the macro is evaluated twice, or the compiler
has to stop evaluting macros twice in case of an error (but I don't know
whether that is possible.)

----------------------------------------------------------------------
 malekith - 02-22-06 15:31 
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You're right, we do restarts in error mode.

It would be hard to prevent the compiler from executing macros in such
situation, because for example the error can be in the code produced by
the macro. Nevertheless it shouldn't be hard to add a special property to
ImplicitCTX() to check if we're running in the error mode (presumably for
the second time).

----------------------------------------------------------------------
 nazgul - 05-01-06 12:50 
----------------------------------------------------------------------
I added the new property in Typer, it is now described in 
http://nemerle.org/Defining_types_from_inside_macros

Issue History
Date Modified  Username       Field                    Change              
======================================================================
02-22-06 10:40 aleksey        New Issue                                    
02-22-06 11:13 nazgul         Note Added: 0001100                          
02-22-06 12:51 aleksey        Note Added: 0001101                          
02-22-06 15:20 steffen        Note Added: 0001103                          
02-22-06 15:31 malekith       Note Added: 0001104                          
02-22-06 21:16 VladD2         Issue Monitored: VladD2                      
05-01-06 12:50 nazgul         Status                   new => resolved     
05-01-06 12:50 nazgul         Resolution               open => fixed       
05-01-06 12:50 nazgul         Assigned To               => nazgul          
05-01-06 12:50 nazgul         Note Added: 0001216                          
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