On Apr 24, 2019, at 11:00 AM, John Rose <john.r.r...@oracle.com> wrote: > > To do this, we will need to make some changes to the JVM > specification (and implementations). Here are the changes > I propose: > > * Relax constraints on CONSTANT_Methodref and CONSTANT_NameAndType > allowing free use of <init> as if it were a regular method name. > * Retain all restrictions on use of <init> via invokespecial. > * Allow an invokestatic to mention <init> (but no other bytecodes). > * Retain all restrictions on definition of <init> methods *in regular > non-inline classfiles* > * Allow an inline classfile to define a <init> method, only with ACC_STATIC > * Require that the type returned by such an <init> method is the containing > class. > (Extra rider: If the class is non-denotable, aka. hidden, returned class > must be Object.)
Something subtle here: Wherever we relax a restriction that affects a use of invokespecial, we usually have to impose it somewhere else. In particular, when the verifier processes a call to <init>, it should (as a new responsibility) ensure that the called descriptor has a void return. An analogous check should look at CONSTANT_MH constants of kind newInvokeSpecial, to make sure the signature has a void return. This is the intention of "retain all restrictions" in the second point, which otherwise contradicts "relax constraints" in the first point.
