RFR: JDK-8237041: AssertionError while parsing unclosed class declarations

[Jan Lahoda]

Hi,

Consider a simplified testcase from the report (the code is obviously 
erroneous):
---
class T {
      String.class,
      String.class,
      //String.class, repeated many times
}

This crashes the parser in a safety code that is intended to prevent 
infinite loops in the parser. This code crashes the parser when there is 
too many errors reported on the same point in the source code.

There are two somewhat independent problematic parts in the code:
-first, consider code like this:
---
class T {
     class C1 {
          class C2 {
          //many more nested classes
//but no closing '}'
---

This is triggering the safety code, as it reports an "premature EOF" 
error for each of the classes, when it cannot find the closing brace. 
The proposed fix for this is to disable the safety code when the token 
that is being handled is an EOF token. (An alternative would be to 
remove the safety check altogether.)

-for code like this:
---
class T {
      class
      class
      class
}
---

the parser will parse this code like:
---
class T {
      class {
          class {
              class {
...
---

I.e. the AST nodes for the classes will be nested. That does not seem 
ideal, as there are no opening braces for the classes. It seems it would 
be better to parse like:
---
class T {
      class {}
      class {}
      class {}
---

The second proposed change in JavacParser attempts to do that, i.e. 
rather return an empty "class" body than continue parsing the class 
content if there is no opening brace. This required some tweaks to 
expected outputs for some tests.

The proposed patch is here:
http://cr.openjdk.java.net/~jlahoda/8237041/webrev.00/index.html

JBS:
https://bugs.openjdk.java.net/browse/JDK-8237041

How does this look?

Thanks,
      Jan