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digitalmars.D.learn - A strange DMD error

reply Keivan Shah <keivan.shah silverleafcaps.com> writes:
Hello,

Today I came across a strange bug while using D with `dmd`. I 
have still not been able to figure out under what conditions does 
it happen but it seems to be a DMD related bug to me. Here is a 
reproducible snippet of the code

```D
import std;

alias DG = void delegate();

class TType
{
}

class MyClass
{
     this(TType t1, TType, double, double[2], double, double, DG, 
TType, TType,
             DG, DG, DG, double, double, double, double, double, 
ulong, bool)
     {
         assert(t1 is null); // I am passing null so should be 
null!
         // NOTE: Seems to work in LDC but fails in DMD.
         writeln("No Bug!");
     }
}

void main()
{
     auto tt = new TType;

     new MyClass(null, tt, 0, [0, 0], 0, 0, null, null, null, 
null, null, null,
             0, 0, 0, 0, 0, 0, false);
}
```
The code gives an assertion failure on the current versions of 
dmd (reproducible on [run.dlang.io](https://run.dlang.io) as 
well) and does not happen when using LDC. The bug seems to be 
sensitive to the number of arguments and their types making it 
reproducible only in very limited cases. I have tried my best to 
reduce it to minimum but still does require these many arguments. 
The end results seems to me like variables are shifted i.e. 
variable 1 gets value of variable 2 and so on, but don't have 
enough proof to support this.

I just wanted some help on the best way to avoid this bug in my 
code and maybe some clue on what causes the error in the first 
place and how should I go about reporting this.

Keivan
Nov 01 2022
next sibling parent reply Imperatorn <johan_forsberg_86 hotmail.com> writes:
On Tuesday, 1 November 2022 at 15:40:04 UTC, Keivan Shah wrote:

 Hello,

 Today I came across a strange bug while using D with `dmd`. I 
 have still not been able to figure out under what conditions 
 does it happen but it seems to be a DMD related bug to me. Here 
 is a reproducible snippet of the code

 [...]


Could be there's some restriction in DMD on number of arguments.

May I ask if this was just an experiment? I hope you're not 
having code like that in the wild 🙏
Nov 01 2022
parent reply Keivan Shah <keivan.shah silverleafcaps.com> writes:
On Tuesday, 1 November 2022 at 15:42:43 UTC, Imperatorn wrote:

 On Tuesday, 1 November 2022 at 15:40:04 UTC, Keivan Shah wrote:

 Hello,

 Today I came across a strange bug while using D with `dmd`. I 
 have still not been able to figure out under what conditions 
 does it happen but it seems to be a DMD related bug to me. 
 Here is a reproducible snippet of the code

 [...]


 Could be there's some restriction in DMD on number of arguments.

 May I ask if this was just an experiment? I hope you're not 
 having code like that in the wild 🙏


Possible, but I think I have had code with more arguments than 
this and it has worked 😅

Unfortunately, not an experiment. Although have replaced the 
types so seems silly now, this is part of my constructor for a 
huge co-coordinator class that takes too many configurable start 
time parameters and so need to pass these many arguments.

Keivan
Nov 01 2022
next sibling parent reply Imperatorn <johan_forsberg_86 hotmail.com> writes:
On Tuesday, 1 November 2022 at 15:49:54 UTC, Keivan Shah wrote:

 On Tuesday, 1 November 2022 at 15:42:43 UTC, Imperatorn wrote:

 On Tuesday, 1 November 2022 at 15:40:04 UTC, Keivan Shah wrote:

 [...]


 Could be there's some restriction in DMD on number of 
 arguments.

 May I ask if this was just an experiment? I hope you're not 
 having code like that in the wild 🙏


 Possible, but I think I have had code with more arguments than 
 this and it has worked 😅

 Unfortunately, not an experiment. Although have replaced the 
 types so seems silly now, this is part of my constructor for a 
 huge co-coordinator class that takes too many configurable 
 start time parameters and so need to pass these many arguments.

 Keivan


Hehe.

One simple thing you could do is to create a struct instead for 
you params and pass that
Nov 01 2022
parent Keivan Shah <keivan.shah silverleafcaps.com> writes:
On Tuesday, 1 November 2022 at 16:06:44 UTC, Imperatorn wrote:

 Hehe.

 One simple thing you could do is to create a struct instead for 
 you params and pass that


Yeah, can do, thanks for the suggestion. But anyways still want 
to see if anyone else has seen this issue, or has a clue about 
what could be happening here. Seems like a rare issue and took up 
too much of my time so better if it's solved or at least 
documented somewhere in the meantime. I have filed an issue for 
this now: https://issues.dlang.org/show_bug.cgi?id=23450
Nov 01 2022
prev sibling parent Tejas <notrealemail gmail.com> writes:
On Tuesday, 1 November 2022 at 15:49:54 UTC, Keivan Shah wrote:

 On Tuesday, 1 November 2022 at 15:42:43 UTC, Imperatorn wrote:

 On Tuesday, 1 November 2022 at 15:40:04 UTC, Keivan Shah wrote:

 Hello,

 Today I came across a strange bug while using D with `dmd`. I 
 have still not been able to figure out under what conditions 
 does it happen but it seems to be a DMD related bug to me. 
 Here is a reproducible snippet of the code

 [...]


 Could be there's some restriction in DMD on number of 
 arguments.

 May I ask if this was just an experiment? I hope you're not 
 having code like that in the wild 🙏


 Possible, but I think I have had code with more arguments than 
 this and it has worked 😅

 Unfortunately, not an experiment. Although have replaced the 
 types so seems silly now, this is part of my constructor for a 
 huge co-coordinator class that takes too many configurable 
 start time parameters and so need to pass these many arguments.

 Keivan


Regarding the too many configurable parameters, the general 
advice is to group all of the params into a `struct` and pass 
that instead as argument to constructor


Pretty wild bug though, definitely a backend thing
Nov 01 2022
prev sibling next sibling parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 11/1/22 11:40 AM, Keivan Shah wrote:

 Hello,
 
 Today I came across a strange bug while using D with `dmd`. I have still 
 not been able to figure out under what conditions does it happen but it 
 seems to be a DMD related bug to me. Here is a reproducible snippet of 
 the code
 
 ```D
 import std;
 
 alias DG = void delegate();
 
 class TType
 {
 }
 
 class MyClass
 {
      this(TType t1, TType, double, double[2], double, double, DG, TType, 
 TType,
              DG, DG, DG, double, double, double, double, double,
ulong, 
 bool)
      {
          assert(t1 is null); // I am passing null so should be null!
          // NOTE: Seems to work in LDC but fails in DMD.
          writeln("No Bug!");
      }
 }
 
 void main()
 {
      auto tt = new TType;
 
      new MyClass(null, tt, 0, [0, 0], 0, 0, null, null, null, null, 
 null, null,
              0, 0, 0, 0, 0, 0, false);
 }
 ```
 The code gives an assertion failure on the current versions of dmd 
 (reproducible on [run.dlang.io](https://run.dlang.io) as well) and does 
 not happen when using LDC. The bug seems to be sensitive to the number 
 of arguments and their types making it reproducible only in very limited 
 cases. I have tried my best to reduce it to minimum but still does 
 require these many arguments. The end results seems to me like variables 
 are shifted i.e. variable 1 gets value of variable 2 and so on, but 
 don't have enough proof to support this.


100% this is a bug in DMD. It should be filed.

I ran some more tests, removing almost any of the parameters or changing 
their types seems to avoid the problem.

I also added a parameter name for the second parameter, and DMD appears 
to be in this case passing the parameters in the wrong order (t1 is 
actually tt, t2 is null)

You can also remove the `import std`, just the assert is enough.

Please file if you can: https://issues.dlang.org

-Steve
Nov 01 2022
parent Keivan Shah <keivan.shah silverleafcaps.com> writes:
On Tuesday, 1 November 2022 at 16:39:57 UTC, Steven Schveighoffer 
wrote:

 100% this is a bug in DMD. It should be filed.

 I ran some more tests, removing almost any of the parameters or 
 changing their types seems to avoid the problem.

 I also added a parameter name for the second parameter, and DMD 
 appears to be in this case passing the parameters in the wrong 
 order (t1 is actually tt, t2 is null)

 You can also remove the `import std`, just the assert is enough.

 Please file if you can: https://issues.dlang.org

 -Steve


Hey, have already filled an issue: 
https://issues.dlang.org/show_bug.cgi?id=23450)
Nov 02 2022
prev sibling parent reply ryuukk_ <ryuukk.dev gmail.com> writes:
This reminds me of an issue i reported last year...

https://issues.dlang.org/show_bug.cgi?id=22583
Nov 01 2022
parent Keivan Shah <keivan.shah silverleafcaps.com> writes:
On Tuesday, 1 November 2022 at 17:05:03 UTC, ryuukk_ wrote:

 This reminds me of an issue i reported last year...

 https://issues.dlang.org/show_bug.cgi?id=22583


This seems to be very similar to the bug I am facing, mostly the 
same underlying issue. Should we somehow link the 2 issues and 
escalate?

Link to my issue: 
https://issues.dlang.org/show_bug.cgi?id=23450)
Nov 02 2022