dart2js -O1 breaks angular tests - then dead code fixes it O_o

[daniel-v]

I'm not sure if it is dart2js or angular_test related issue. Due to lack of better idea, I'm pretty much duplicating https://github.com/angulardart/angular/issues/1952 here too.

Basically what I have observed is that having a bit of specially prepared dead code influences the compilation/optimization process of dart2js in such a way that it makes things work. I expect my code to work without the dead code but it doesn't. Without further ado, repro code here

Repro steps:

1. grab a stagehand angular starter project
2. throw in the test and the build.yaml file from gist
3. pub run build_runner test -r -- -p chrome

-r command line argument is important. DDC works fine.

There are a number of things that must be present in order for this to happen:

1. Component should use AsyncPipe on a special Stream
2. The implementation of that Stream must be "mockito-like" - overriding noSuchMethod
3. dart2js compiler must have -O1 or above optimization level

Until this point, component test fails, though I think it should pass. To fix it, there are 2 approaches:

1. add a bit of dead code like in the gist
2. use -O0 optimization level for dart2js

My expectation: Both reachable tests pass without dead code

What happens: Without dead code, the component test fails, though it shouldn't

Env

• Dart SDK version: 2.10.4 (stable) (Wed Nov 11 13:35:58 2020 +0100) on "linux_x64"
• Angular 5.3, 6

Uhm, so I'm wondering, is it an angular_test bug or did I stumble onto something compiler related? (There is a 3rd option: I'm a idiot and I'm missing something)

[daniel-v]

(hihi, had my fun, wonder if this workaround will pass CR: https://gist.github.com/daniel-v/e734a6b5f0f5ba5ead26130ddc67cb93 )