Use min_specialization in libcore

[matthewjasper]

Getting TrustedRandomAccess to work is the main interesting thing here.

• get_unchecked is now an unstable, hidden method on Iterator
• The contract for TrustedRandomAccess is made clearer in documentation
• Fixed a bug where Debug would create aliasing references when using the specialized zip impl
• Added tests for the side effects of next_back and nth.

closes #68536

[rust-highfive]

r? @cramertj

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

[nagisa]

Only made a very basic initial pass, got distracted before I could go through the whole PR.

[nagisa]

Why does this need to become pub?

[matthewjasper]

It's now used in the interface of Iterator

[nagisa]

Given that the default implementation simply panic!()s, this is not an unsafety invariant, is it?

[bors]

☔ The latest upstream changes (presumably #73643) made this pull request unmergeable. Please resolve the merge conflicts.

[Muirrum]

@rustbot modify labels to: +S-waiting-on-author -S-waiting-on-review

[JohnTitor]

Let's r? @nagisa as they left some review comments.

[nagisa]

@bors r+

[nagisa]

Do we actually want to enforce that the 2nd iterator consumes 1 more value than from the first iterator? I think this could go either way, but I would at least leave a comment to that effect so that a change in this behaviour wouldn’t immediately appear invalid.

[nagisa]

Oh well, this will need a rebase, but r=me once that's done.

Sorry for taking so long to get around to this.

[matthewjasper]

@bors r=nagisa

[bors]

📌 Commit dbad8c9 has been approved by nagisa

[bors]

⌛ Testing commit dbad8c9 with merge 1dc99bb058f144c8f4f64b005e546c10f301901b...

[rust-log-analyzer]

The job mingw-check of your PR failed (pretty log, 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.

Build completed successfully in 0:02:10
+ /scripts/validate-toolstate.sh
Cloning into 'rust-toolstate'...
<Nothing changed>
Traceback (most recent call last):
  File "../../src/tools/publish_toolstate.py", line 283, in <module>
    validate_maintainers(repo, github_token)
  File "../../src/tools/publish_toolstate.py", line 84, in validate_maintainers
    'Accept': 'application/vnd.github.hellcat-preview+json',
  File "/usr/lib/python3.6/urllib/request.py", line 223, in urlopen
    return opener.open(url, data, timeout)
  File "/usr/lib/python3.6/urllib/request.py", line 532, in open
    response = meth(req, response)
  File "/usr/lib/python3.6/urllib/request.py", line 642, in http_response
    'http', request, response, code, msg, hdrs)
  File "/usr/lib/python3.6/urllib/request.py", line 570, in error
    return self._call_chain(*args)
  File "/usr/lib/python3.6/urllib/request.py", line 504, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.6/urllib/request.py", line 650, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 403: Forbidden
  local time: Wed Aug 19 22:47:09 UTC 2020
  network time: Wed, 19 Aug 2020 22:47:09 GMT
== end clock drift check ==
== end clock drift check ==
##[error]Process completed with exit code 1.
Terminate orphan process: pid (6409) (node)
Terminate orphan process: pid (6433) (python)

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 @rust-lang/infra. (Feature Requests)

[bors]

💔 Test failed - checks-actions

[matthewjasper]

@bors retry

[bors]

⌛ Testing commit dbad8c9 with merge 2f15b6b842776d00d2eb9369deeb7dcd1b3a3baa...

[bors]

💔 Test failed - checks-azure

[matthewjasper]

@bors retry

[bors]

⌛ Testing commit dbad8c9 with merge d9d4d39...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: nagisa
Pushing d9d4d39 to master...

[the8472]

@matthewjasper I'm currently thinking how to extend TrustedRandomAccess to drop types, one piece I am currently not understanding is why __iterator_get_unchecked was moved from TrustedRandomAccess to Iterator but not its other methods.

[matthewjasper]

__iterator_get_unchecked was moved because it sometimes needs the bounds on the Iterator impl. The other methods were not because I wanted to minimize what was added to Iterator.