Angular generally supports cycles between components in the same NgModule.
We have a mechanism of moving the component scope declaration into the
NgModule file in this case. This ensures that Angular never itself
introduces an import which creates a cycle.
What happens if the cycle already exists in the user's program, though, is a
bit different. In these cases, the "correct" emit for Angular is to generate
the component scope (whether direct or remote) inside of a closure, to
prevent evaluating the scope's references until module evaluation is
complete and all cyclic imports have been resolved. We don't want to do this
for *all* scopes because the code size cost of emitting a function wrapper
is non-zero.
In this fix, we take the presence of a `forwardRef` in a component's
`imports` or in an NgModule `declarations` or `imports` as a sign that
component scopes emitted into those files need to be protected against
cyclic references. In a future commit, we may introduce a warning or error
if cyclic imports are not protected behind `forwardRef` in these cases, but
this will take some time to implement.
PR Close#46139
f0bf29a24d