Bug: different hashcodes for equal generic types, on Android

[Erhannis]

Under some conditions, the hashcode of a generic type shows up as 0, and non-zero from an equal (but not identical) type. Occurred on Android (10 and 12 but not 6.0.1), but not on Linux native, nor on Chrome. May be related to #45060 - I even discovered the problem under similar circumstances.

Here's code to demonstrate it:

class Foo<T> {
}

class Bar {
}

void bar1<T>() {
  log("Foo<Bar>: ${Foo<Bar>} ${Foo<Bar> == Foo<Bar>} ${(Foo<Bar>).hashCode}");
  log("  Foo<T>: ${Foo<T>} ${Foo<T> == Foo<Bar>} ${(Foo<T>).hashCode}");
}
void bar2<T>() {
  log("Foo<Bar>: ${Foo<Bar>} ${Foo<Bar> == Foo<Bar>} ${(Foo<Bar>).hashCode}");
  log("       T: ${T} ${T == Foo<Bar>} ${(T).hashCode}");
}

void test() {
  bar1<Bar>();
  bar2<Foo<Bar>>();
}

This gives e.g.

[log] Foo<Bar>: Foo<Bar> true 393223570
[log]   Foo<T>: Foo<Bar> true 0
[log] Foo<Bar>: Foo<Bar> true 393223570
[log]        T: Foo<Bar> true 393223570

As you can see, all forms are equal to Foo<Bar>, but Foo<T> (where T is set to Bar) has a different hashcode, namely 0.

Tried this on two computers...actually, now I have one Android phone where it works right and two where it doesn't. Uh, here's a table of things:

Flutter 3.3.0-0.2.pre • channel beta • https://github.com/flutter/flutter.git
Framework • revision 7ac27ac8e6 (13 days ago) • 2022-08-02 14:35:08 -0700
Engine • revision d1e7dc18bf
Tools • Dart 2.18.0 (build 2.18.0-271.4.beta) • DevTools 2.15.0
:
Android 12 - bug
:
:
:
Flutter 3.0.5 • channel stable • https://github.com/flutter/flutter.git
Framework • revision f1875d570e (5 weeks ago) • 2022-07-13 11:24:16 -0700
Engine • revision e85ea0e79c
Tools • Dart 2.17.6 • DevTools 2.12.2
:
Android 10 - bug
Android 12 - bug
Android 6.0.1 - correct
Linux desktop (Ubuntu 20.04.4 64bit) - correct
Chrome 102.0.5005.115 64bit - correct

[Boucaa]

Ran into this as well today. I created a simplified example below to show the issue

class Foo<T> {
  final brokenType = List<T>;
}

void main() {
  final a = Foo<Object>();
  print(a.brokenType.hashCode);
}

Output on Android (Dart 3, Flutter 3.10)

0

Output on web (dartpad)

680950264

[mraleph]

@alexmarkov could you take a look?