Deal with exception type mismatches between the source and target methods

[khatchad]

Consider the following valid input source code:

package p;

import java.io.IOException;

interface I {
    void m() throws Exception;
}

abstract class A implements I {
    public void m() throws IOException {
    }

    void n() throws IOException {
        m();
    }

    void q(I i) throws Exception {
        i.m();
    }
}

Suppose that A.m() is the source method. In migrating it to I, we now have a mismatch between the exception types thrown. Specifically, I.m() declares that it throws Exception, while A.m() declares that it throws IOException. In fact, picking either of these exception types for the target method would result in an error.

There are two issues here, I believe. First, we should not allow exception type mismatches (will create a new issue for this). Second, we need an issue to possibly relax this precondition. In the above situation, there's just nothing we can do. However, using intra-procedural analysis, it is possible to see which exception type to pick.

[khatchad]

I believe we do have a check for the basic case mentioned above. Looks like this issue is for the relaxation.