Make IpvXAddr::new const fns and the well known addresses associated constants

[faern]

Implements/fixes #44582

I just got a PR towards libc (rust-lang/libc#1044) merged. With the new feature added in that PR it is now possible to create in6_addr instances as consts. This enables us to finally make the constructors of the IP structs const fns and to make the localhost/unspecified addresses associated constants, as agreed in the above mentioned tracking issue.

I also added a BROADCAST constant. Personally this is the well known address I tend to need the most often.

[rust-highfive]

r? @TimNN

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[rust-highfive]

⚠️ Warning ⚠️

• These commits modify submodules.

[faern]

I realize now we might want to use the same feature gate name for the associated constants and the constructors. I did not think about that before. But I'll wait for some feedback before doing anything about it.

[faern]

It should be noted that we can get away without unlocking #![feature(const_int_ops)] if desired. We could have a local const fn hton(u32) -> u32 that takes care of converting to big endian.

We can also get the associated constants without making the constructors const fns. We can just have private const constructors that we use in the normal constructors and for creating the associated constants, but the public constructors can be non-const if that is desired for some reason. I went with making the constructors const since I think that would be very useful in general. Having the IP constructors const is what drove me to implement this :)

[TimNN]

Thanks for your PR! This looks generally good, I'll take a detailed look tomorrow. Having an unstable const-constructor and using const_int_ops is fine, I think.

[TimNN]

@bors r+

[bors]

📌 Commit 312cdb4 has been approved by TimNN

[bors]

⌛ Testing commit 312cdb4 with merge 362961dac287cb17ecc0e79ed39dbd90092f82ce...

[bors]

💔 Test failed - status-travis

[rust-highfive]

The job x86_64-gnu-aux of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:29:56] [RUSTC-TIMING] proc_macro test:false 18.180
[00:29:56]    Compiling syntax_ext v0.0.0 (file:///checkout/src/libsyntax_ext)
[00:30:33] [RUSTC-TIMING] syntax_ext test:false 36.797

Broadcast message from root@travis-job-21a0d1b5-843e-408b-a860-9ddf81b9ea94
 (unknown) at 17:44 ...
The system is going down for power off NOW!
[00:35:02] Makefile:28: recipe for target 'all' failed
[00:35:02] Makefile:28: recipe for target 'all' failed
[00:35:02] Session terminated, terminating shell... ...terminated.
[00:35:02] make: *** [all] Terminated

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 143.
travis_time:start:08ef844a
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[TimNN]

@bors retry

• Host shut down during build travis-ci/travis-ci#4924

[bors]

⌛ Testing commit 312cdb4 with merge facbc12...

[bors]

💔 Test failed - status-travis

[faern]

@TimNN There, I found it with the help of some Redox people on IRC. Apparently Redox does not use in6_addr from libc, but rather define their own version deep down in libstd. This should hopefully build now!

[TimNN]

Awesome work, @faern!

@bors r+

[bors]

📌 Commit 6e7bbff6f66ab74a49b4f2aacb5d0073b0ebf1ee has been approved by TimNN

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout use-modern-alignment-libc (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self use-modern-alignment-libc --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

warning: Cannot merge binary files: src/Cargo.lock (HEAD vs. heads/homu-tmp)
Auto-merging src/Cargo.lock
CONFLICT (content): Merge conflict in src/Cargo.lock
Automatic merge failed; fix conflicts and then commit the result.

[faern]

Trying to get anything merged in Cargo.lock is a pain 😅 And I strictly don't need that any more, since the fix was to change in6_addr in libstd itself. So if it fails one more time because of a merge conflict I'll skip trying to bump libc in Cargo.lock.

[TimNN]

@bors r+

[bors]

📌 Commit c0041f4 has been approved by TimNN

[bors]

⌛ Testing commit c0041f4 with merge ebe8df4...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: TimNN
Pushing ebe8df4 to master...