[Issue 20471] TypeInfo_Array incorrectly initialized

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20471

Simen Kjaeraas <simen.kjaras at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |simen.kjaras at gmail.com
            Summary|DMD Crash                   |TypeInfo_Array incorrectly
                   |                            |initialized

--- Comment #2 from Simen Kjaeraas <simen.kjaras at gmail.com> ---
The leaf node in the stack trace is object.TypeInfo_Array.toString(), and
looking at that code
(https://github.com/dlang/druntime/blob/2cc13ead1e7e535ef8ebd1f600d4ffb508a93f98/src/object.d#L532):

override string toString() const { return value.toString() ~ "[]"; }

This will fail if value is null. Is it null though?

unittest {
    auto a = typeid("");
    import std.stdio;
    writeln(a.toString());
}

> immutable(char)[]

Doesn't look like it.

unittest {
    auto a = typeid("");
    assert(a.value !is null, "a.value is null!");
}

> [unittest] a.value is null!

Uhm...

It seems something is special cased when handling TypeInfo, so that the code in
toString() doesn't run at that point. For whatever reason, this
short-circuiting doesn't happen inside DMD, and so it crashes.

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