assertion failed: !self.contains(&sheet)

[mateon1]

Found with domato.

<style>
* { display: none}
</style>

assertion failed: !self.contains(&sheet) (thread LayoutThread PipelineId { namespace_id: PipelineNamespaceId(0), index: PipelineIndex(NonZero(1)) }, at /shared/dev/rust/servo/components/style/stylesheet_set.rs:330)
stack backtrace:
   0:     0x5650a7c91884 - backtrace::backtrace::libunwind::trace
                        at /shared/dev/rust/servo/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.2/src/backtrace/libunwind.rs:53
                         - backtrace::backtrace::trace<closure>
                        at /shared/dev/rust/servo/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.2/src/backtrace/mod.rs:42
   1:     0x5650a7c849ef - backtrace::capture::{{impl}}::new
                        at /shared/dev/rust/servo/.cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.2/src/capture.rs:64
   2:     0x5650a128a78e - servo::main::{{closure}}
                        at /shared/dev/rust/servo/ports/servo/main.rs:130
   3:     0x5650a7f6a456 - std::panicking::rust_panic_with_hook
                        at /checkout/src/libstd/panicking.rs:578
   4:     0x5650a6a95955 - std::panicking::begin_panic<&str>
                        at /checkout/src/libstd/panicking.rs:538
   5:     0x5650a6b8c047 - style::stylesheet_set::{{impl}}::append<style::stylesheets::stylesheet::DocumentStyleSheet>
                        at /shared/dev/rust/servo/components/style/stylesheet_set.rs:330
   6:     0x5650a6b8c762 - style::stylesheet_set::{{impl}}::append_stylesheet<style::stylesheets::stylesheet::DocumentStyleSheet>
                        at /shared/dev/rust/servo/components/style/stylesheet_set.rs:441
   7:     0x5650a70c6cea - style::stylist::{{impl}}::append_stylesheet
                        at /shared/dev/rust/servo/components/style/stylist.rs:601
   8:     0x5650a1ba82c1 - layout_thread::{{impl}}::handle_reflow
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:1189
   9:     0x5650a1ba316d - layout_thread::{{impl}}::handle_request_helper::{{closure}}
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:700
  10:     0x5650a1a49f53 - profile_traits::time::profile<(),closure>
                        at /shared/dev/rust/servo/components/profile_traits/time.rs:124
  11:     0x5650a1ba1d6e - layout_thread::{{impl}}::handle_request_helper
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:697
  12:     0x5650a1ba0b0b - layout_thread::{{impl}}::handle_request
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:644
  13:     0x5650a1b9fe23 - layout_thread::{{impl}}::start
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:557
  14:     0x5650a1c51829 - layout_thread::{{impl}}::create::{{closure}}::{{closure}}
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:316
  15:     0x5650a1bc3284 - profile_traits::mem::{{impl}}::run_with_memory_reporting<closure,fn(profile_traits::mem::ReportsChan) -> script_layout_interface::message::Msg,script_layout_interface::message::Msg,std::sync::mpsc::Sender<script_layout_interface::message::Msg>>
                        at /shared/dev/rust/servo/components/profile_traits/mem.rs:63
  16:     0x5650a1ea34a3 - layout_thread::{{impl}}::create::{{closure}}
                        at /shared/dev/rust/servo/components/layout_thread/lib.rs:315
  17:     0x5650a1de2a2a - std::sys_common::backtrace::__rust_begin_short_backtrace<closure,()>
                        at /checkout/src/libstd/sys_common/backtrace.rs:136
  18:     0x5650a1de4883 - std::thread::{{impl}}::spawn::{{closure}}::{{closure}}<closure,()>
                        at /checkout/src/libstd/thread/mod.rs:394
  19:     0x5650a1d8931a - std::panic::{{impl}}::call_once<(),closure>
                        at /checkout/src/libstd/panic.rs:296
  20:     0x5650a1a815e2 - std::panicking::try::do_call<std::panic::AssertUnwindSafe<closure>,()>
                        at /checkout/src/libstd/panicking.rs:480
  21:     0x5650a7f715ec - panic_unwind::__rust_maybe_catch_panic
                        at /checkout/src/libpanic_unwind/lib.rs:99
  22:     0x5650a1a807dc - std::panicking::try<(),std::panic::AssertUnwindSafe<closure>>
                        at /checkout/src/libstd/panicking.rs:459
  23:     0x5650a1de3af5 - std::panic::catch_unwind<std::panic::AssertUnwindSafe<closure>,()>
                        at /checkout/src/libstd/panic.rs:361
  24:     0x5650a1de46ab - std::thread::{{impl}}::spawn::{{closure}}<closure,()>
                        at /checkout/src/libstd/thread/mod.rs:393
  25:     0x5650a1e25ce3 - alloc::boxed::{{impl}}::call_box<(),closure>
                        at /checkout/src/liballoc/boxed.rs:728
  26:     0x5650a7f690db - alloc::boxed::{{impl}}::call_once<(),()>
                        at /checkout/src/liballoc/boxed.rs:738
                         - std::sys_common::thread::start_thread
                        at /checkout/src/libstd/sys_common/thread.rs:24
                         - std::sys::imp::thread::{{impl}}::new::thread_start
                        at /checkout/src/libstd/sys/unix/thread.rs:90
  27:     0x7fdca4609493 - start_thread
  28:     0x7fdca4136abe - __clone
  29:                0x0 - <unknown>
ERROR:servo: assertion failed: !self.contains(&sheet)

[emilio]

This seems to be double-adding the UA sheets in the layout thread.