add &Root<T> checker

[mrmiywj]

Thank you for contributing to Servo! Please replace each [ ] by [X] when the step is complete, and replace __ with appropriate data:

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #11137 (github issue number if applicable).

Either:

• There are tests for these changes OR
• These changes do not require tests because _____

Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process.

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This change is

[highfive]

Heads up! This PR modifies the following files:

• @wafflespeanut: python/tidy/servo_tidy/tidy.py

[wafflespeanut]

We also need to update the tests in servo_tidy_tests, so that we can make sure that we're getting the warning.

[highfive]

New code was committed to pull request.

[wafflespeanut]

Well, this won't be needing a new function, but well, it's just a test... 😄

[wafflespeanut]

Note that the raised warning should be verified in test_tidy.py. Also, ./mach test-tidy will show the files which make use of &Root<T>. We should replace them before we land.

[mrmiywj]

Does it mean I need to replace them by hands? It's must be a great amount of work..

[wafflespeanut]

Not if we use find and awk or sed to do the replacement. Moreover, the failed travis build shows that there are only 3 occurrences of the thing in our codebase :)

[mrmiywj]

There maybe some problems if we change &Root to &T. It will cause type mismatch.
In this file mentioned in travis build log.

[highfive]

New code was committed to pull request.

[highfive]

New code was committed to pull request.

[cbrewster]

Is there any reason why we have a from_rooted it seems like we could change all those to from_ref. Or even better, we could move that to Root<T> As the comment there suggests.

[jdm]

Hmm, unroot and the PartialEq implementation for Root<T> are a problem. I'm not sure what to do about those.

[nox]

IMO RootCollection::unroot should be inlined directly in Root::<T>::drop because you shouldn't be able to unroot something without losing the Root itself (even more so because unroot isn't even unsafe).

For PartialEq, we could maybe remove the impl and see how many comparisons now need an additional bunch of &* magic.

[KiChjang]

What's the status of this?

[mrmiywj]

@KiChjang
Hi, Sorry for that I was busy with my finals.
I will go on this in this week

[jdm]

The other status is that we need to figure out how to avoid a couple valid uses of : Root<T> that exist in the codebase, otherwise this can't merge.

[jdm]

#11522 should address all the problem instances, so this should be ready to merge as soon as that PR does!

[highfive]

New code was committed to pull request.

[jdm]

@bors-servo: r+

[bors-servo]

📌 Commit a17ae72 has been approved by jdm

[bors-servo]

⌛ Testing commit a17ae72 with merge 93f137f...

[bors-servo]

💔 Test failed - linux-rel

[highfive]

  ▶ FAIL [expected PASS] /css-transforms-1_dev/html/transform-table-007.htm
  └   → /css-transforms-1_dev/html/transform-table-007.htm a5c014b20ef1363bea6f24eda28c7efb7c45698a
/css-transforms-1_dev/html/reference/transform-blank-ref.htm fa6407b1acbbfea27e27061e7d1bdeca98e4a728
Testing a5c014b20ef1363bea6f24eda28c7efb7c45698a == fa6407b1acbbfea27e27061e7d1bdeca98e4a728

[wafflespeanut]

@bors-servo retry #11574

[bors-servo]

⚡ Previous build results for android, arm32, arm64, linux-dev, mac-dev-unit, mac-rel-css, mac-rel-wpt, windows are reusable. Rebuilding only linux-rel...

[bors-servo]

☀️ Test successful - android, arm32, arm64, linux-dev, linux-rel, mac-dev-unit, mac-rel-css, mac-rel-wpt, windows