http://d.puremagic.com/issues/show_bug.cgi?id=2816

           Summary: Sudden-death static assert is not very useful
           Product: D
           Version: 1.042
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: patch
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: clugdbug@yahoo.com.au


Sudden-death static asserts were introduced due to comment #2 of bugzilla 77: http://d.puremagic.com/issues/show_bug.cgi?id=77

However, they make static assert rather useless, since it gives you absolutely no context. To make it useful again,

In staticassert.c, line 68 (in DMD2.027):
        error("is false");
        if (!global.gag)
            fatal();
---
change this to:
        error("(%s) is false", exp->toChars());
---

(ie, remove the global.gag test).


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #1 from bugzilla@digitalmars.com  2009-04-07 04:21 -------
The static assert does give you file/line, so it does give context. But I'll add the expression print, too.

But I think static assert errors should be fatal. They usually involve misconfigured code, it is pointless to continue.


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http://d.puremagic.com/issues/show_bug.cgi?id=2816


clugdbug@yahoo.com.au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|patch                       |




------- Comment #2 from clugdbug@yahoo.com.au  2009-04-07 05:55 -------
(In reply to comment #1)
> The static assert does give you file/line, so it does give context. But I'll add the expression print, too.
> 
> But I think static assert errors should be fatal. They usually involve misconfigured code, it is pointless to continue.
> 

Yes, there will not be any more meaningful errors. But you still need a back
trace.
If the static assert occurs in (say) a library template, knowing that it
happened in std.functional at line 92 doesn't help very much -- you want to
know where the problem is in _your_ code. (That's a real example, BTW).

Actually, I'll have another try, and see if I can create a backtrace, and THEN make it a fatal error. So I'm retracting this patch.


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http://d.puremagic.com/issues/show_bug.cgi?id=2816


kamm-removethis@incasoftware.de changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch




------- Comment #3 from kamm-removethis@incasoftware.de  2009-04-07 10:21 -------
Don, LDC already implemented template instantiation traces. Check StaticAssert::semantic2 and TemplateInstance::printInstantiationTrace. I emailed Walter about them at the time. If desired, I can provide a patch against DMD.


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #4 from clugdbug@yahoo.com.au  2009-04-07 10:47 -------
(In reply to comment #3)
> Don, LDC already implemented template instantiation traces. Check StaticAssert::semantic2 and TemplateInstance::printInstantiationTrace. I emailed Walter about them at the time. If desired, I can provide a patch against DMD.

That'd be great!


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #5 from shro8822@vandals.uidaho.edu  2009-04-07 11:07 -------

For that matter, if template errors could all be given optional (some flag?)
stack traces (not just chained errors) that would be cool.

I'm thinking somthing like:

template error foo bla bla bla.
invoked at file.d:7235 from TBar
invoked at file.d:752 from TBaz
invoked at code.d:7235 from Bling
...

maybe (another flag?) some formatted printing of the args to (limited to 80
columns)


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #6 from kamm-removethis@incasoftware.de  2009-04-08 07:43 -------
Created an attachment (id=318)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=318&action=view)
template instantiation trace patch

patch against DMD 1.043, superficially tested

Note that this originated as a hack and might have been possible without adding tinst to Scope and TemplateInstance. There were discussions about including only certain template instantiations in such a trace: http://www.mail-archive.com/digitalmars-d@puremagic.com/msg03614.html


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #7 from clugdbug@yahoo.com.au  2009-04-09 02:43 -------
Christian -- Thanks, this is fantastic!
I've modified it so that it detects recursive template instantiations -- this
dramatically reduces the size of the trace. A patch will follow shortly.


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #8 from clugdbug@yahoo.com.au  2009-04-09 04:18 -------
Created an attachment (id=319)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=319&action=view)
patch for dmd2.028

I've adjusted the backtrace in two ways:
(1) displays line numbers in what I believe is a more IDE-friendly manner;
(2) detects recursive template instantiations and collapses them into a single
line.
I've made no changes other than to the InstantiationTrace function.


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http://d.puremagic.com/issues/show_bug.cgi?id=2816





------- Comment #9 from clugdbug@yahoo.com.au  2009-04-09 04:24 -------
Error messages generated from my patch for the code below:
bug.d(2): Error: static assert  (0) is false
bug.d(9):        instantiatied from here: bar!()
bug.d(14):        100 recursive instantiations from here: foo!(196)
bug.d(19):        253 recursive instantiations from here: baz!(300)

(Oops -- just realised I there's a typo in "instantiated" in the non-recursive
messages. That's easy to fix).
Note that it detects the recursive instantiation in foo!(), even though it is
instantiated from three different places.

--------
template bar() {
   static assert(0);
}

template foo(int N) {
  static if (N>0) {
     static if (N&1) alias foo!(N-3) foo;
     else alias foo!(N-1) foo;
  } else alias bar!() foo;
}

template baz(int M) {
   static if (M<50) {
     alias foo!(M*4) baz;
   } else alias baz!(M-1) baz;
}

void main() {
  int x = baz!(300);
}


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