[Issue 20812] _d_assocarrayliteralTX segfault assigning a shared associative array an AA literal

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20812

Steven Schveighoffer <schveiguy at gmail.com> changed:

           What    |Removed                     |Added
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           Keywords|                            |safe, wrong-code
                 CC|                            |schveiguy at gmail.com

--- Comment #3 from Steven Schveighoffer <schveiguy at gmail.com> ---
I further diagnosed this. You don't need to declare the shared aa separately,
this will do:

```d
void main() { shared aa = ["abc": "123"]; }
```

If you declare `aa` as const instead, the `ti` parameter passed to
`_d_assocarrayliteralTX` is a legit `TypeInfo_AssociativeArray`. However, when
you use shared, the `ti` parameter is pointing to the wrapping
`TypeInfo_Shared`. 

Note that this is a *reinterpret cast*, not a dynamic cast, and so it really
thinks it's pointing at a `TypeInfo_AssociativeArray`. Therefore the `key`
field doesn't actually exists, and is garbage.

I'm not sure on LDC if this is a similar problem but it's possible since it's
reading invalid memory it happens to work? I tend to think not.

I ran on run.dlang.io for all compilers, and all segfault. So this has been
happening for a while.

const, immutable, and inout all do not have this problem, only shared.

I also confirmed this is a problem on gdc.

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