• d-bugmail puremagic.com (47/47) Nov 01 2022 https://issues.dlang.org/show_bug.cgi?id=23450

d-bugmail puremagic.com writes:

https://issues.dlang.org/show_bug.cgi?id=23450

          Issue ID: 23450
           Summary: Unexpected constructor behaviour in DMD in rare cases
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody puremagic.com
          Reporter: keivan.shah silverleafcaps.com

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

```
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 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.

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