JDK-8191112: javac OutOfMemoryError caused by "-Xlint:exports" option

[Jan Lahoda]

Hi,

Consider an automatic module "dep" with class "dep.Dep", and additional 
automatic modules ext1 and ext2.

When javac has these on the modulepath, and compiles a module like this:
---
module mod {
     requires dep;
     exports api;
}

package api;

public class Api extends dep.Dep {}
---

-Xlint:exports can be used to report exported APIs that refer to types 
potentially inaccessible to the clients. In this case, the supertype of 
api.Api may be inaccessible unless the client has a dependency on "dep", 
so the lint will warn about that. But since the dep, ext1 and ext2 are 
automatic modules, each of the modules "requires transitive" the other 
automatic modules, and the check may go into an infinite loop.

Moreover, for code like this:
---
module mod {
requires transitive ext1;
exports api;
}
---

"dep.Dep" is accessible using requires transitive edges of the automatic 
modules, hence the warning/lint is not printed.

That does not seem quite right, an explicit "requires transitive dep" 
dependency would be better, otherwise the changes in the module path can 
lead to surprising behavior.

The suggested patch is to simply ignore the dependencies of automatic 
modules in the check - that should avoid the infinite loop and print the 
warning in the "requires transitive ext1" case.

Bug: https://bugs.openjdk.java.net/browse/JDK-8191112
Webrev: http://cr.openjdk.java.net/~jlahoda/8191112/webrev.00/

What do you think?

Thanks,
     Jan