[12] RFR (M) JDK-8205611: Improve the wording of LinkageErrors to include module and class loader information

[Lois Foltan]

Please review this change to migrate existing loader constraint 
LinkageErrors to the new error message format proposal.  The actual 
wording of the loader constraint messages has not changed.  Module and 
class loader information have been moved into the error message's REASON 
section.  This change also removes the method 
java_lang_ClassLoader::describe_external() in favor of 
Klass::class_in_module_of_loader().

open webrev at http://cr.openjdk.java.net/~lfoltan/bug_jdk8205611/webrev/
bug link https://bugs.openjdk.java.net/browse/JDK-8205611

JDK-8166633 outlines a new proposal where error messages follow a format 
of ERRROR: PROBLEM (REASON) where the PROBLEM is aggressively simple 
(and definitely avoids arbitrary-length loader names) so the REASON 
bears all the cost of explaining the PROBLEM with more specifics.  See 
the proposal in more detail at 
https://bugs.openjdk.java.net/browse/JDK-8166633. The new utility method 
Klass::class_in_module_of_loader() implements the proposed format.

Some example text:

(JDK 11) 'DuplicateLE_Test_Loader_IF' @<id> (instance of 
PreemptingClassLoader, child of 'app' 
jdk.internal.loader.ClassLoaders$AppClassLoader) attempted duplicate 
interface definition for test.J.
to
(JDK 12) loader 'DuplicateLE_Test_Loader_IF' @6eeee674 attempted 
duplicate interface definition for test.J. (test.J is in unnamed module 
of loader 'DuplicateLE_Test_Loader_IF' @6eeee674, parent loader 'app')


(JDK 11) loader constraint violation: loader PreemptingClassLoader @<id> 
(instance of PreemptingClassLoader, child of 'app' 
jdk.internal.loader.ClassLoaders$AppClassLoader) wants to load class 
test.D_ambgs. A different class with the same name was previously loaded 
by 'app' (instance of jdk.internal.loader.ClassLoaders$AppClassLoader).
to
(JDK 12) loader constraint violation: loader PreemptingClassLoader 
@5bc79a1c wants to load class test.D_ambgs. A different class with the 
same name was previously loaded by 'app'. (test.D_ambgs is in unnamed 
module of loader 'app')


(JDK 11) loader constraint violation for class test.Task: when selecting 
overriding method test.Task.m()Ltest/Foo; the class loader 
PreemptingClassLoader @<id> (instance of PreemptingClassLoader, child of 
'app' jdk.internal.loader.ClassLoaders$AppClassLoader) of the selected 
method's type test.Task, and the class loader 'app' (instance of 
jdk.internal.loader.ClassLoaders$AppClassLoader) for its super type 
test.J have different Class objects for the type test.Foo used in the 
signature
to
(JDK 12) loader constraint violation for class test.Task: when selecting 
overriding method test.Task.m()Ltest/Foo; the class loader 
PreemptingClassLoader @7884e077 of the selected method's type test.Task, 
and the class loader 'app' for its super type test.J have different 
Class objects for the type test.Foo used in the signature (test.Task is 
in unnamed module of loader PreemptingClassLoader @7884e077, parent 
loader 'app'; test.J is in unnamed module of loader 'app')


Testing: hs-tier(1-3), jdk-tier(1-3) complete
                hs-tier(4,5) in progress
                JCK vm, lang in progress

Thanks,
Lois