Fix 'reinterpret' casts of StringExp to static array with implicit extension

[kinke]

Fixes issue 19639.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	19639	regression	Initializing static array with slice enum of different length crashes the compiler

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#9321"

[kinke]

Currently segfaults the compiler (the EMPTY_STRING buffer (StringExp.string) as memcpy source is null).

[kinke]

Currently likely to fail or crash as the compile-time memcpy reads beyond the SMALL_STRING buffer.

[ghost]

This looks good but the PR can be submitted for the stable branch as it fixes a regression.

[kinke]

I had it on stable and then switched to master, as I deemed it better suited (sooner in nightlies). It's a sort of regression - the crash for the first test block happens since v2.071, while the read-beyond-src-buffer has apparently been there since v2.068 (https://run.dlang.io/is/oPq799).

Implicit extension was apparently added with v2.066.

[ghost]

all right, pink @thewilsonator

[kinke]

Hmm, the bugzilla issue wasn't auto-closed...

[wilzbach]

Hmm, the bugzilla issue wasn't auto-closed.

The Bugzilla integration closes only things when they are merged in master automatically. Stable was turned off as too many people complained about lots of emails on new releases. Though IMHO that's a lot less worse than an integration which doesn't seem to work...

[kinke]

@wilzbach: That's why I was wondering, this targeted master.

[wilzbach]

Sorry. Only read this from my phone. Then I also don't know what went wrong 🤷‍♂️
Maybe because GitHub services are deprecated and to be removed eventually?

[wilzbach]

Ah well, there's an explanation: https://developer.github.com/changes/2018-04-25-github-services-deprecation

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