RFR: JDK-8235564: javac crashes while compiling incorrect method invocation with member reference

[Jan Lahoda]

Hi,

Consider code like:
public class Test {
     static void test() {
         existingWithoutFunctional(Test::undefined);
     }

     private static void existingWithoutFunctional(String parameter) {}
}

javac crashes on this (please see the bug for the stack trace). The 
reason for this is that while there are two errors in the source code: 
a) passing member reference to a parameter that is not of a functional 
type; b) the member reference refers to a method that does not exist, no 
error is reported. The first error is suppressed because the parameter 
is erroneous, and it is expected an error was already issued for it 
(this is fine).

The second error is mostly accidentally suppressed because 
Attr.visitReference will get "String" and pt(), and hence 
getTargetInfo() will fail to find the functional type, and most of the 
processing/verification is skipped, and this causes the problem. The 
problem is while doing recovery 
DeferredAttr.RecoveryDeferredTypeMap.recover will use the non-functional 
formal parameter type as the expected target type. This was an attempt 
to improve error recovery, but seems to go too far. The proposal is to 
use the formal parameter type only if it is a functional type.

As a result, for the example above, the javac reponse will be:
$ javac Test.java
Test.java:3: error: invalid method reference
         existingWithoutFunctional(Test::undefined);
                                   ^
   cannot find symbol
     symbol:   method undefined()
     location: class Test
1 error

Which is the same as in JDK 11.
cr.openjdk.java.net/~jlahoda/8235564/webrev.00/

Proposed webrev:

JBS: https://bugs.openjdk.java.net/browse/JDK-8235564

How does this look?

Thanks,
     Jan