fmt: impl fmt::Pointer for smart pointer types

[richo]

I believe this should fix the issue. Opening a PR to ensure noone duplicates effort, I'm running check now.

Closes#24091

[rust-highfive]

r? @pcwalton

(rust_highfive has picked a reviewer for you, use r? to override)

[richo]

This builds and does something reasonable on my machine. Is it worth adding a test?

Also, are there any other smart pointer types that I should impl for? The only other one that looks relevant is P in rustc that would be useful for shotgun debugging, and perhaps Box ?

[richo]

Bonus impls for the other smart pointers I could find

[alexcrichton]

I think that this is infinitely recursive, did you mean &**self?

[richo]

Oops. Is Box specialcased in some way in the compiler? I can't seem to extract the Unique within using tuple access or a destructuring match.

 expected `Box<T>`,
found `boxed::Box<_>`
(expected box,
found struct `boxed::Box`) [E0308]
/Users/richo/code/ext/rust/src/liballoc/boxed.rs:282 &Box(uniq) => fmt::Pointer::fmt(&uniq, f)

[alexcrichton]

Yeah Box is pretty special, and I'm not actually sure the definition has much bearing on what you can do with the type itself. You'll probably want to pull out &T from &Box<T> and then format that.

[alexcrichton]

Could you add a smoke test for the Box, Rc, and Arc impls as well?

[richo]

Sure, I'll work out how I goofed box and add the test.

[richo]

I added a test, and made it pad pointers to native pointer width if no format is specified, which I bellieve to be correct. Let me know if I should rip that off though.

Make check is running on my machine, but I tested that the test case added works with a stage1.

r? @alexcrichton

[richo]

(make check passes locally, on osx)

[alexcrichton]

Could this change be left to another PR?

[richo]

Yup, np.

[richo]

Rebased, this is now only the fmt::Pointer implementation

[alexcrichton]

Thanks! Could you also squash the commits together? Other than that r=me

[richo]

Done, thanks!

[alexcrichton]

@bors: r+ a329a61

[bors]

⌛ Testing commit a329a61 with merge 6436e34...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-32-nopt-t, auto-win-32-opt, auto-win-64-nopt-t, auto-win-64-opt