RFR: 8373094: javac may fail because of unattributed break in a loop

[Jan Lahoda]

Consider a case like this:

package test;
public class Intermediate<T> extends Base<T> {}

package test;
public class Base<T> {
    public void t(Missing<T> m) {}
}
package test;
public class Missing<T> {}

this is compiled, and then `Missing` is deleted. Then a test file is compiled with the above classes on the classpath:

$ cat src/test/Test.java 
package test;
public class Test extends Intermediate<String> {
    private void test() {
        while (true) { break; }
    }
}
$ javac -XDdev -XDshould-stop.at=FLOW -d classes -classpath classes src/test/Test.java
src/test/Test.java:2: error: cannot access Missing
public class Test extends Intermediate<String> {
       ^
  class file for test.Missing not found
1 error
An exception has occurred in the compiler (25.0.1). Please file a bug against the Java compiler via the Java bug reporting page (https://bugreport.java.com) after checking the Bug Database (https://bugs.java.com) for duplicates. Include your program, the following diagnostic, and the parameters passed to the Java compiler in your report. Thank you.
java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AliveAnalyzer.clearPendingExits(Flow.java:631)
        at jdk.compiler/com.sun.tools.javac.comp.Flow$AliveAnalyzer.visitMethodDef(Flow.java:619)
...


The reason is that the `CompletionFailure` will be thrown from `chk.checkCompatibleSupertypes(tree.pos(), c.type);`, and since that's before attributing the method bodies, the method bodies will remain blank. And hence the `break` will have no target set, and `Flow` will fail on it.

I spent some time trying to figure out if we could improve handling on `CompletionFailure`s more generally, so that we would not need to catch them on more-or-less arbitrary places. But everything I was able to do so far didn't really improve the situation. So the proposal herein is to catch and handle the `CompletionFailure` on some place.

-------------

Commit messages:
 - Improving test.
 - 8373094: javac may fail because of unattributed break in a loop

Changes: https://git.openjdk.org/jdk/pull/28680/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28680&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373094
  Stats: 167 lines in 2 files changed: 160 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/28680.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28680/head:pull/28680

PR: https://git.openjdk.org/jdk/pull/28680