Implement concept of dirty root

[nox]

No description provided.

[highfive]

Heads up! This PR modifies the following files:

• @asajeffrey: components/script/dom/bindings/cell.rs, components/script/dom/document.rs, components/script/dom/shadowroot.rs, components/script/dom/node.rs, components/script/dom/element.rs and 2 more
• @KiChjang: components/script/dom/bindings/cell.rs, components/script/dom/document.rs, components/script/dom/shadowroot.rs, components/script/dom/node.rs, components/script/dom/element.rs and 2 more
• @emilio: components/layout/traversal.rs, components/style/driver.rs

[highfive]

Warning

• These commits modify unsafe code. Please review it carefully!
• These commits modify style, layout, and script code, but no tests are modified. Please consider adding a test!

[nox]

I hit the wrong button, I wanted to make a draft PR. Oh well.

@bors-servo try

[bors-servo]

⌛ Trying commit 2795709 with merge 600748b...

[bors-servo]

💔 Test failed - status-taskcluster

[nox]

My code is doing bad stuff when the document's children are changed, looking into it.

[nox]

@bors-servo try=wpt

[bors-servo]

⌛ Trying commit ec3a72b with merge 5f9bc0e...

[bors-servo]

💔 Test failed - status-taskcluster

[nox]

  ▶ CRASH [expected OK] /_webgl/conformance/ogles/GL/gl_FrontFacing/gl_FrontFacing_001_to_001.html
  │ 
  │ error: XDG_RUNTIME_DIR not set in the environment.
  │ libEGL warning: No hardware driver found, falling back to software rendering
  │ called `Option::unwrap()` on a `None` value (thread LayoutThread PipelineId { namespace_id: PipelineNamespaceId(1), index: PipelineIndex(1) }, at /repo/components/layout/wrapper.rs:151)
  │    0: servo::backtrace::print
  │    1: servo::main::{{closure}}
  │    2: std::panicking::rust_panic_with_hook
  │              at src/libstd/panicking.rs:515
  │    3: rust_begin_unwind
  │              at src/libstd/panicking.rs:419
  │    4: core::panicking::panic_fmt
  │              at src/libcore/panicking.rs:111
  │    5: core::panicking::panic
  │              at src/libcore/panicking.rs:54
  │    6: <T as layout::wrapper::ThreadSafeLayoutNodeHelpers>::restyle_damage
  │    7: profile_traits::time::profile
  │    8: layout_thread::LayoutThread::handle_reflow
  │    9: profile_traits::time::profile
  │   10: layout_thread::LayoutThread::handle_request_helper
  │   11: layout_thread::LayoutThread::start
  │   12: profile_traits::mem::ProfilerChan::run_with_memory_reporting
  │   13: std::sys_common::backtrace::__rust_begin_short_backtrace
  │   14: core::ops::function::FnOnce::call_once{{vtable.shim}}
  │   15: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/42abbd8878d3b67238f3611b0587c704ba94f39c/src/liballoc/boxed.rs:1008
  │   16: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
  │              at /rustc/42abbd8878d3b67238f3611b0587c704ba94f39c/src/liballoc/boxed.rs:1008
  │       std::sys::unix::thread::Thread::new::thread_start
  │              at src/libstd/sys/unix/thread.rs:87
  │   17: start_thread
  │   18: __clone
  │ [2020-05-11T12:24:59Z ERROR servo] called `Option::unwrap()` on a `None` value
  │ Pipeline failed in hard-fail mode.  Crashing!
  │ thread panicked while processing panic. aborting.
  └ thread panicked while processing panic. aborting.

I must be missing something somewhere.

This can only happen if there is an element which doesn't have any data, but I don't see how that can happen through the dirty root, given that the parent without the data should be dirty too.

[nox]

I guess I can try with 2020 meanwhile. I had to do some fancy stuff in 2013 for incremental restyle, and that stuff is not needed on the 2020 side.

@bors-servo try=wpt-2020

[nox]

@bors-servo try=wpt-2020

[bors-servo]

⌛ Trying commit ad47321 with merge 78feae1...

[bors-servo]

💔 Test failed - status-taskcluster

[bors-servo]

☔ The latest upstream changes (presumably #26464) made this pull request unmergeable. Please resolve the merge conflicts.

[bors-servo]

⌛ Trying commit 155e6af with merge 59c174b...

[bors-servo]

💔 Test failed - status-taskcluster

[nox]

@bors-servo try

[bors-servo]

⌛ Trying commit 0b2c21f with merge 692bdc0...

[bors-servo]

💔 Test failed - status-taskcluster

[nox]

@bors-servo try

Everything should be ok now.

r? @SimonSapin

[SimonSapin]

Looks good!

@bors-servo r+

[bors-servo]

📌 Commit 036f123 has been approved by SimonSapin

[bors-servo]

⌛ Testing commit 036f123 with merge 79b6758...

[bors-servo]

☀️ Test successful - status-taskcluster
Approved by: SimonSapin
Pushing 79b6758 to master...