type inference: javac is incorrectly applying capture conversion during incorporation

ADDITIONAL SYSTEM INFORMATION :
Ubuntu 18.04 LTS

java version "10.0.1" 2018-04-17
Java(TM) SE Runtime Environment 18.3 (build 10.0.1+10)
Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.1+10, mixed mode)



A DESCRIPTION OF THE PROBLEM :
First reported here: https://stackoverflow.com/questions/50928300

Type inference for generics has changed between Java8 and Java9/10 breaking special-case usages e.g. of the hamcrest library. Workarounds seem generally possible by providing more type information.

REGRESSION : Last worked in version 8u172

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Try to compile given code with javac from Java9/10.



EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Code compiles as it does in Java8.
ACTUAL -
Code does not compile, type errors like:


    Error:(21, 28) java: incompatible types: inference variable U has incompatible bounds
    equality constraints: com.Test.B<? super com.Test.D>
    upper bounds: com.Test.B<? super capture#1 of ? super com.Test.D>,java.lang.Object



---------- BEGIN SOURCE ----------
class Test1 {
    class A<S> { } class B<S> { } class C<S> { } class D { }

    <T> A<B<? super T>> foo() { return null; }

    <U> C<U> bar(A<U> a1, A<? super U> a2) { return null; }

    C<B<? super D>> c = bar(foo(), foo());
}


class Test2 {
    class A<S> { } class B<S> { } class C<S> { } class D { }

    <T> A<B<? super T>> foo() { return null; }

    <U> C<U> bar(A<? super U> a) { return null; }

    C<B<? super D>> c = bar(foo());
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Provide more type information such as casting arguments.

FREQUENCY : always