Tree-shaking unused superclass method fails with factory constructor #30963
Description
In the following code:
class Super {
Super();
factory Super.sub() = Sub;
void foo() {
throw "super foo";
}
void bar() {
foo();
// Throw to avoid inlining this method.
throw "";
}
}
class Sub extends Super {
void foo() {
throw "sub foo";
}
}
main() async {
new Super.sub().bar();
}Super.foo() is unreachable, but dart2js (as of 0c005a3) fails to tree-shake it:
$ dart2js test.dart
$ grep -n "super error" out.js
4936: throw H.wrapException("super foo");
This seems to only happen if Sub is constructed via a factory constructor on Super (redirecting or otherwise), and foo() is called from another method in Super (in this case, bar()).
This came up in practice when trying to reduce the code size of the http package and its dependencies.