Extend C-DEREF guideline to say smart pointers should always be transparent in Debug representation

[dtolnay]

The canonical Debug implementation for any type that implements Deref is:

Debug::fmt(&**self, formatter)

This principle came up during libs team discussion of rust-lang/rust#48553.

[KodrAus]

Seems reasonable to me!

[KodrAus]

@rfcbot fcp merge

[KodrAus]

@rfcbot fcp merge

This suggests a guideline that smart pointers inherit the Debug implementation of their pointee.

[rfcbot]

Team member @KodrAus has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @KodrAus
• @dtolnay
• @m-ou-se
• @sfackler
• @withoutboats

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

psst @KodrAus, I wasn't able to add the final-comment-period label, please do so.

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

The RFC will be merged soon.

psst @KodrAus, I wasn't able to add the finished-final-comment-period label, please do so.

[jonhoo]

Given this passed FCP, should the change be made?