Dart2's ResizeObserver being broken by Dart minifier - dart

Question

i have the following snippet of Dart2 code (Dart 2.7) which works 100% when running in dev mode, but fails when running it in production mode
ResizeObserver rowObserver;
final ResizeObserverCallback rowObserverCallback = (List<ResizeObserverEntry> entries, ResizeObserver observer){
print("inside row observer callback");
for (ResizeObserverEntry entry in entries) {
print(" ... entry is ${entry.runtimeType} and entry.target is ${entry.target.runtimeType}");
//resizeRow(entry.target as TableRowElement);
}
};
rowObserver = ResizeObserver(rowObserverCallback);
Changing content in the table row now correctly outputs
inside row observer callback
... entry is ResizeObserverEntry and entry.target is TableRowElement
When building the Dart code and running it, this same snippet generates the following error:
Uncaught TypeError: Instance of 'minified:c1': type 'minified:c1' is
not a subtype of type 'List'
Running is done with
pub global run webdev serve web:9999
While building is done with
pub global run webdev build --output=web:build --release
i've tried changing --release to --no-release, but not sure how to run it in that mode.
Changing to dynamic, i'm getting the exact same issue with minification:
final ResizeObserverCallback rowObserverCallback = (dynamic blah1, dynamic blah2){
Changing to Object, at least i'm getting into the resize callback:
final ResizeObserverCallback rowObserverCallback = (Object blah1, Object blah2){
print("inside row observer callback");
print(blah1.runtimeType);
print(blah2.runtimeType);
print(blah1 is List<ResizeObserverEntry>);
which outputs:
inside row observer callback
minified:c1
minified:bQ
false
Force casting it seems to throw a casting error:
final ResizeObserverCallback rowObserverCallback = (Object blah1, Object blah2){
print("inside row observer callback");
print(blah1.runtimeType);
print(blah2.runtimeType);
print(blah1 is List<ResizeObserverEntry>);
for (ResizeObserverEntry entry in blah1 as List<ResizeObserverEntry>) {
print(" ... entry is ${entry.runtimeType} and entry.target is ${entry.target.runtimeType}");
}
};
Uncaught CastError: Instance of 'minified:c1': type 'minified:c1' is
not a subtype of type 'List'
Force casting it to a single instance of ResizeObserverEntry fails as well
final ResizeObserverCallback rowObserverCallback = (Object blah1, Object blah2){
print("inside row observer callback");
print(blah1.runtimeType);
print(blah2.runtimeType);
print(blah1 is List<ResizeObserverEntry>);
for (ResizeObserverEntry entry in [blah1 as ResizeObserverEntry]) {
print(" ... entry is ${entry.runtimeType} and entry.target is ${entry.target.runtimeType}");
//resizeRow(entry.target as TableRowElement);
}
};
Uncaught CastError: Instance of 'minified:c1': type 'minified:c1' is
not a subtype of type 'minified:bp'
pubspec.yaml in case it's relevant:
name: blah
version: 0.0.2
description: Blah Blah
environment:
sdk: ">=2.6.0 <3.0.0"
dependencies:
angular: ^5.3.1
angular_forms: ^2.1.2
http: any
js: ^0.6.0
logging: "^0.11.3+1"
html: any
json_serializable: any
blahvo:
path: ../blah-vo
dev_dependencies:
angular_test: 2.3.0
build_runner: ^1.5.2
build_test: ^0.10.2
build_web_compilers: ^2.0.0
test: ^1.0.0
So how do i actually make ResizeObserver work in Dart2?
It seems ResizeObserver is very broken in Dart2, at least in production / release mode, it works fine in dev mode.
EDIT1:
Some snippets from the generated JS where c1 is referenced:
J.c1.prototype={
k:function(a,b){H.p(b,H.j(a,0))
if(!!a.fixed$length)H.a7(P.E("add"))
a.push(b)},
u.c1=new ResizeObserver(H.aU(new L.j6(),2))},
this.a.c1.unobserve(a)},
r.c1.observe(a)},
if(a.constructor==Array)return J.c1.prototype
c1:function c1(a){this.$ti=a},
_.f3=_.c1=_.bg=_.c0=_.f2=null},
Trying to shoot in the dark, but not hitting anything
final ResizeObserverCallback rowObserverCallback = (Object blah1, Object blah2){
print("inside row observer callback");
print(blah1.runtimeType);
print(blah2.runtimeType);
print(blah1 is List<ResizeObserverEntry>);
print(blah1 is ResizeObserverEntry);
print(blah1 is TableRowElement);
print(blah1 is List<TableRowElement>);
print(blah1 is JsArray);
print(blah1 is NumToArrayPipe);
print(blah1 == null);
print(blah1 is Function);
print(blah1 is ResizeObserver);
all of them prints false
Taking a chance and replacing blah1 with blah2
final ResizeObserverCallback rowObserverCallback = (Object blah1, Object blah2){
print("inside row observer callback");
print(blah1.runtimeType);
print(blah2.runtimeType);
print(blah2 is List<ResizeObserverEntry>);
print(blah2 is ResizeObserverEntry);
print(blah2 is TableRowElement);
print(blah2 is List<TableRowElement>);
print(blah2 is JsArray);
print(blah2 is NumToArrayPipe);
print(blah2 == null);
print(blah2 is Function);
print(blah2 is ResizeObserver);
and the last one prints true as expected
EDIT2:
using JS Interopt, i'm doing console.log to see what the type of blah1 actually is and it turns out it is a DartObject containing an Array ...
context["console"].callMethod("log", [blah1]);
What should i cast blah1 to in order to get access to the list of ResizeObserverEntry ?
EDIT3
I made a demo that can reproduce the error:
bug_resize_observer.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div class="div1" style="background-color: red">
<textarea style="padding: 10px; margin: 10px;">
TESTING
</textarea>
</div>
<div class="div2" style="background-color: blue">
.
</div>
<script defer src="bug_resize_observer.dart.js"></script>
</body>
</html>
and bug_resize_observer.dart.js:
import "dart:html";
void main() {
final DivElement div1 = querySelector("div.div1");
final DivElement div2 = querySelector("div.div2");
final ResizeObserver divResizeObserver = ResizeObserver((List<ResizeObserverEntry> blah1, ResizeObserver blah2) {
print("inside divResizeObserverCallback");
for (ResizeObserverEntry entry in blah1) {
div2.style.height = "${entry.target.clientHeight}px";
}
});
divResizeObserver.observe(div1);
}
In DEV mode, the blue div mimicks the height of the red div when you resize the text area:
In release mode, you only get errors:
EDIT4:
Logged a bug here:
https://github.com/dart-lang/sdk/issues/40961