Implement the preserveWrapperCallback API to allow our DOM objects to be stored in WeakMaps.

[nickdesaulniers]

➜  servo git:(master) ✗ RUST_BACKTRACE=1 ./build/servo http://localhost:4000
Error at http://localhost:4000/dist.js:27: TypeError: document.createElement(...).getContext is not a function

evaluate_script failed

Not sure if getContext is not a method of an HTMLCanvasElement, or if createElement is not a method of the document object?

[jdm]

Both of those exist and are tested. What is the code that isn't working?

http://mxr.mozilla.org/servo/source/components/script/dom/htmlcanvaselement.rs#241

[nickdesaulniers]

https://www.dropbox.com/s/l2oywvluzwjwy9o/demo.zip?dl=0

[jdm]

Assertion failure: cx->runtime()->preserveWrapperCallback, at /Users/jdm/.cargo/git/checkouts/mozjs-06d7f04b6dbb8a8e/master/mozjs/js/src/jsweakmap.cpp:332
Process 47230 stopped
* thread #7: tid = 0xac5c7, 0x0000000102329347 servo`TryPreserveReflector(cx=0x000000010a41cc40, obj=JS::HandleObject at 0x000000011a9f3720) + 263 at jsweakmap.cpp:332, name = 'ScriptTask PipelineId(0)', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
    frame #0: 0x0000000102329347 servo`TryPreserveReflector(cx=0x000000010a41cc40, obj=JS::HandleObject at 0x000000011a9f3720) + 263 at jsweakmap.cpp:332
   329          (obj->is<ProxyObject>() &&
   330           obj->as<ProxyObject>().handler()->family() == GetDOMProxyHandlerFamily()))
   331      {
-> 332          MOZ_ASSERT(cx->runtime()->preserveWrapperCallback);
   333          if (!cx->runtime()->preserveWrapperCallback(cx, obj)) {
   334              JS_ReportErrorNumber(cx, GetErrorMessage, nullptr, JSMSG_BAD_WEAKMAP_KEY);
   335              return false;
(lldb) bt
error: need to add support for DW_TAG_base_type '()' encoded with DW_ATE = 0x7, bit_size = 0
* thread #7: tid = 0xac5c7, 0x0000000102329347 servo`TryPreserveReflector(cx=0x000000010a41cc40, obj=JS::HandleObject at 0x000000011a9f3720) + 263 at jsweakmap.cpp:332, name = 'ScriptTask PipelineId(0)', stop reason = EXC_BAD_ACCESS (code=1, address=0x0)
  * frame #0: 0x0000000102329347 servo`TryPreserveReflector(cx=0x000000010a41cc40, obj=JS::HandleObject at 0x000000011a9f3720) + 263 at jsweakmap.cpp:332
    frame #1: 0x0000000102303b9c servo`SetWeakMapEntryInternal(cx=0x000000010a41cc40, mapObj=Handle<js::WeakMapObject *> at 0x000000011a9f3810, key=JS::HandleObject at 0x000000011a9f3808, value=JS::HandleValue at 0x000000011a9f3800) + 236 at jsweakmap.cpp:368
    frame #2: 0x0000000102349825 servo`WeakMap_set_impl(cx=0x000000010a41cc40, args=CallArgs at 0x000000011a9f3990) + 789 at jsweakmap.cpp:405
    frame #3: 0x000000010233bb2f servo`bool JS::CallNonGenericMethod<&(cx=0x000000010a41cc40, args=CallArgs at 0x000000011a9f3a10)), &(WeakMap_set_impl(JSContext*, JS::CallArgs))>(JSContext*, JS::CallArgs) + 127 at CallNonGenericMethod.h:100
    frame #4: 0x0000000102303414 servo`js::WeakMap_set(cx=0x000000010a41cc40, argc=2, vp=0x000000010b876668) + 100 at jsweakmap.cpp:415
    frame #5: 0x0000000101b6d9eb servo`js::CallJSNative(cx=0x000000010a41cc40, native=0x00000001023033b0, args=0x000000011a9f4340)(JSContext*, unsigned int, JS::Value*), JS::CallArgs const&) + 187 at jscntxtinlines.h:235
    frame #6: 0x0000000101b27c15 servo`js::Invoke(cx=0x000000010a41cc40, args=CallArgs at 0x000000011a9f4340, construct=NO_CONSTRUCT) + 1269 at Interpreter.cpp:502
    frame #7: 0x0000000101b41030 servo`Interpret(cx=0x000000010a41cc40, state=0x000000011a9f7218) + 51744 at Interpreter.cpp:2609
    frame #8: 0x0000000101b34529 servo`js::RunScript(cx=0x000000010a41cc40, state=0x000000011a9f7218) + 585 at Interpreter.cpp:452
    frame #9: 0x0000000101b27d56 servo`js::Invoke(cx=0x000000010a41cc40, args=CallArgs at 0x000000011a9f7a10, construct=NO_CONSTRUCT) + 1590 at Interpreter.cpp:521
    frame #10: 0x000000010222cf11 servo`js::fun_call(cx=0x000000010a41cc40, argc=8, vp=0x000000010b876218) + 577 at jsfun.cpp:1239
    frame #11: 0x0000000101b6d9eb servo`js::CallJSNative(cx=0x000000010a41cc40, native=0x000000010222ccd0, args=0x000000011a9f83d0)(JSContext*, unsigned int, JS::Value*), JS::CallArgs const&) + 187 at jscntxtinlines.h:235
    frame #12: 0x0000000101b27c15 servo`js::Invoke(cx=0x000000010a41cc40, args=CallArgs at 0x000000011a9f83d0, construct=NO_CONSTRUCT) + 1269 at Interpreter.cpp:502
    frame #13: 0x0000000101b41030 servo`Interpret(cx=0x000000010a41cc40, state=0x000000011a9fb2e0) + 51744 at Interpreter.cpp:2609
    frame #14: 0x0000000101b34529 servo`js::RunScript(cx=0x000000010a41cc40, state=0x000000011a9fb2e0) + 585 at Interpreter.cpp:452
    frame #15: 0x0000000101b4d6bd servo`js::ExecuteKernel(cx=0x000000010a41cc40, script=JS::HandleScript at 0x000000011a9fb408, scopeChainArg=0x000000011a356060, thisv=0x000000011a9fb480, type=EXECUTE_GLOBAL, evalInFrame=(ptr_ = 0), result=0x000000011a9fc040) + 1149 at Interpreter.cpp:660
    frame #16: 0x0000000101b4db07 servo`js::Execute(cx=0x000000010a41cc40, script=JS::HandleScript at 0x000000011a9fb4f0, scopeChainArg=0x000000011a356060, rval=0x000000011a9fc040) + 999 at Interpreter.cpp:702
    frame #17: 0x000000010217af55 servo`Evaluate(cx=0x000000010a41cc40, scope=JS::HandleObject at 0x000000011a9fb770, optionsArg=0x000000010a41bf10, srcBuf=0x000000011a9fb7d0, rval=JS::MutableHandleValue at 0x000000011a9fb768) + 1029 at jsapi.cpp:4183
    frame #18: 0x000000010217b2b4 servo`Evaluate(cx=0x000000010a41cc40, optionsArg=0x000000010a41bf10, chars=0x000000011b0ac000, length=77783, rval=JS::MutableHandleValue at 0x000000011a9fb808) + 132 at jsapi.cpp:4218
    frame #19: 0x000000010217b21d servo`JS::Evaluate(cx=0x000000010a41cc40, optionsArg=0x000000010a41bf10, chars=0x000000011b0ac000, length=77783, rval=JS::MutableHandleValue at 0x000000011a9fb848) + 61 at jsapi.cpp:4272
    frame #20: 0x00000001018ddf7f servo`js::jsapi::Evaluate2(cx=0x000000010a41cc40, options=0x000000010a41bf10, chars=0x000000011b0ac000, length=77783, rval=MutableHandle<js::jsapi::Value> at 0x000000011a9fb8a0) + 111 at jsapi.rs:8981
    frame #21: 0x00000001018ddf05 servo`jsapi::Evaluate2::he412378402173c2eqoi + 37
    frame #22: 0x0000000100c27bb5 servo`script::dom::window::&'a T.ScriptHelpers::evaluate_script_on_global_with_result(self=0x000000011b042600, code=(data_ptr = "(function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require==\"function\"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error(\"Cannot find module '\"+o+\"'\");throw f.code=\"MODULE_NOT_FOUND\",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require==\"function\"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){\nmodule.exports = function (gl, data, elemPerVertex, attribute) {\n  var buffer = gl.createBuffer();\n  if (!buffer) throw new Error('Failed to create buffer.');\n  gl.bindBuffer(gl.ARRAY_BUFFER, buffer);\n  gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);\n  gl.vertexAttribPointer(attribute, elemPerVertex, gl.FLOAT, false, 0, 0);\n  gl.enableVertexAttribArray(attribute);\n  return buffer;\n};\n\n\n},{}],2:[function(require,module,exports){\n// watchify main.js -o dist.js -v -d\n\nvar glShader = require('gl-shader');\nvar createQuat = require('gl-q...", length = 77783), filename=(data_ptr = "file:///Users/jdm/Downloads/demo/dist.js", length = 40), rval=MutableHandle<js::jsapi::Value> at 0x000000011a9fbc78) + 1429 at window.rs:632
    frame #23: 0x0000000101190e2c servo`script::dom::htmlscriptelement::HTMLScriptElement::execute(self=0x000000011b067000, load=ScriptOrigin at 0x000000011a9fc3a8) + 3436 at htmlscriptelement.rs:405
    frame #24: 0x000000010118f0e6 servo`script::dom::htmlscriptelement::ScriptContext.AsyncResponseListener::response_complete(self=0x000000011b042c18, status=Result<(), collections::string::String> at 0x000000011a9fcad8) + 390 at htmlscriptelement.rs:170
    frame #25: 0x000000010155c776 servo`net_traits::ResponseAction::process(self=ResponseAction at 0x000000011a9fcd68, listener=&AsyncResponseListener at 0x000000011a9fcd58) + 502 at lib.rs:120
    frame #26: 0x00000001011989a6 servo`script::network_listener::ListenerRunnable<T>.Runnable::handler(self=0x0000000114036880) + 502 at network_listener.rs:47
    frame #27: 0x000000010131f51c servo`script::script_task::ScriptTask::handle_msg_from_script(self=0x000000011aa00450, msg=MainThreadScriptMsg at 0x000000011a9fd590) + 636 at script_task.rs:918
    frame #28: 0x00000001013277cb servo`script::script_task::ScriptTask::handle_msgs(self=0x000000011aa00450) + 7515 at script_task.rs:825
    frame #29: 0x000000010131c571 servo`script::script_task::ScriptTask::start(self=0x000000011aa00450) + 33 at script_task.rs:684
    frame #30: 0x000000010131c53d servo`fnfn + 29 at script_task.rs:491
    frame #31: 0x000000010131c2b1 servo`script::mem::ProfilerChan::run_with_memory_reporting<closure,fn(self=0x000000011aa00788, f=closure at 0x000000011a9ffcf0, reporter_name=String at 0x000000011a9ffcd8, channel_for_reporter=Box<ScriptChan> at 0x000000011a9ffcc8, msg=0x0000000101062570) -> script::script_task::CommonScriptMsg,script::script_task::CommonScriptMsg,Box<ScriptChan>> + 577 at mem.rs:61
    frame #32: 0x0000000101312a0a servo`fnfn + 3258 at script_task.rs:490
    frame #33: 0x0000000101311cb8 servo`fnfn + 104 at task.rs:31
    frame #34: 0x0000000101311c08 servo`script::boxed::F.FnBox<A>::call_box(self=0x0000000116842280, args=<unavailable>) + 104 at boxed.rs:512
    frame #35: 0x0000000100bec34c servo`script::boxed::Box<FnBox<A, Output = R>+ Send + 'a>.FnOnce<A>::call_once(self=Box<FnBox<()>> at 0x000000011aa00bc0, args=<unavailable>) + 60 at boxed.rs:528
    frame #36: 0x0000000100bebf2e servo`fnfn + 78 at mod.rs:309
    frame #37: 0x0000000100bebeda servo`script::rt::unwind::try::try_fn<closure>(opt_closure=0x000000011aa00cf0) + 58 at mod.rs:164
    frame #38: 0x000000010281cce9 servo`__rust_try + 9
    frame #39: 0x0000000102818941 servo`rt::unwind::try::inner_try::h39d984f71e9cc780Tyw + 97
    frame #40: 0x0000000100bebe44 servo`script::rt::unwind::try<closure>(f=closure at 0x000000011aa00d08) + 100 at mod.rs:136
    frame #41: 0x0000000100bebcbc servo`fnfn + 412 at mod.rs:309
    frame #42: 0x0000000100bec5ad servo`script::boxed::F.FnBox<A>::call_box(self=0x0000000116824160, args=<unavailable>) + 77 at boxed.rs:512
    frame #43: 0x000000010281bfde servo`sys::thread::Thread::new::thread_start::h999b3790b6d4b23deXv + 142
    frame #44: 0x00007fff928ae899 libsystem_pthread.dylib`_pthread_body + 138
    frame #45: 0x00007fff928ae72a libsystem_pthread.dylib`_pthread_start + 137
    frame #46: 0x00007fff928b2fc9 libsystem_pthread.dylib`thread_start + 13

[jdm]

Looks like we need to implement the preserveWrapperCallback API to allow our DOM objects to be stored in WeakMaps.

[nox]

WeakMaps? Where are they? Do they do what I think they do? Can we use them from Rust for ranges and things like that?

[jdm]

They're SpiderMonkey things. I don't even know the situation for using them from C++, let alone Rust.

[jdm]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap

[Ms2ger]

This involves calling js::jsapi::SetPreserveWrapperCallback in ScriptTask::new_rt_and_cx() (components/script/script_task.rs). The argument should be a new preserve_wrapper function that unconditionally returns true.

[Ms2ger]

... as well as adding tests in window and worker contexts.

[jdm]

#7620 has a great testcase for the window context that we can copy.

[Manishearth]

Minimimized GitHub testcase:

<html><head></head><body>
<input id="a">
    <script type="text/javascript">
    x = new WeakMap();
    x.set(document.getElementById("a"), 2);
    </script>
</body></html>

[Manishearth]

@jdm Also, rust-mozjs expects a function returning a u8, whereas actually it is -> bool. I'm not sure if that part is autogenerated, but should we fix that?

[jdm]

I do not know anything about the implications of using bool/u8 in FFI, unfortunately.

[Ms2ger]

Use JSTrue for now.

[Manishearth]

A naive return JSTrue impl of this seems to segfault a lot. Not E-Easy.