[Coding Guideline]: Ensure reads of union fields produce valid values

[manhatsu]

Added new guideline on unions by @rcseacord.

This is the same content as #270 but moved to the feature branch.

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[rcseacord]

@PLeVasseur @felix91gr I did a final cleanup and this rule LGTM. Please review & approve

[iglesias]

I left a couple of comments. Otherwise it was all clear. One is a question about a line I wasn't sure about and the other just a typo fix suggestion.

[felix91gr]

@PLeVasseur @felix91gr I did a final cleanup and this rule LGTM. Please review & approve

Alright, it goes into the queue.

[PLeVasseur]

@PLeVasseur @felix91gr I did a final cleanup and this rule LGTM. Please review & approve

Alright, it goes into the queue.

Hey @felix91gr -- did you take a look at this one yet? I'd like it to be reviewed before we queue it up

(I'll try to make time to review some of @rcseacord's latest ones tomorrow, this included, if it's not been reviewed by you yet)

[felix91gr]

I'd like it to be reviewed before we queue it up

@PLeVasseur ah, sorry! I forgot we have a Merge Queue as well. I meant it as my own task queue, my bad. I haven't reviewed it yet

[PLeVasseur]

Hey thanks for pulling this together @manhatsu and @rcseacord

Given that adding the bibliography bit touches quite a few other things, I'd suggest backing that out of this PR if you'd like the guideline to be reviewed on its merits and merged sooner than later.

I've opened issue #306 to track the work towards the work for a bibliography.

[manhatsu]

There is a duplication of URL in these two documents:
expressions/gui_Bib7x9KmPq2nL.rst.inc and types-and-traits/gui_0cuTYG8RVYjg.rst.inc.
bibliography.md says I should consider this, but how can I actually solve this?
I think it's fine if both have the source entry...

[PLeVasseur]

There is a duplication of URL in these two documents: expressions/gui_Bib7x9KmPq2nL.rst.inc and types-and-traits/gui_0cuTYG8RVYjg.rst.inc. bibliography.md says I should consider this, but how can I actually solve this? I think it's fine if both have the source entry...

Yeah, you're right. I didn't have this implemented correctly. Duplicate URLs should be fine, what I wanted to have was for the same URL to force consistent referencing to be used.

I've pushed #335 which should fix this.

Please take a look at the following and rebase:
https://github.com/rustfoundation/safety-critical-rust-coding-guidelines/blob/main/docs/bibliography.md