Add is_documentation for IPv6

[achanda]

This function returns true if the given IPv6 is reserved for
documentation. Also, reject this block in the is_global check

[alexcrichton]

Could you elaborate on the rationale for this addition as well? We aren't currently very principled about the query methods we have so I'm largely just curious.

[achanda]

RFC 3849 defines this range to be used for documentation only [1]. No end hosts should be assigned addresses in this range. Thus this address can not be a globally routable address. This is how python behaves for this range

$ python3
Python 3.5.1 (default, Mar 13 2016, 13:29:57) 
[GCC 4.2.1 Compatible Apple LLVM 7.0.2 (clang-700.1.81)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import ipaddress
>>> ip = ipaddress.ip_address('2001:db8::')
>>> ip.is_global
False
>>> ip.is_private
True

Please let me know if I should clarify something else.

[1] https://tools.ietf.org/html/rfc3849

[bors]

☔ The latest upstream changes (presumably #32211) made this pull request unmergeable. Please resolve the merge conflicts.

[alexcrichton]

Seems reasonable to me! Tagging with T-libs just to make sure this comes up during triage.

[alexcrichton]

The libs team discussed this during triage yesterday and the decision was to merge, thanks @achanda!

@bors: r+ aa22b4e

[bors]

⌛ Testing commit aa22b4e with merge a77d7bd...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-mac-ios-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt, auto-win-msvc-64-opt-rustbuild