Updated ARM Spec

[Joe Darcy]

Joe Darcy wrote:
> Greetings.
>
> Starting with Project Coin proposal for Automatic Resource Management 
> (ARM), in consultation with Josh Bloch, Maurizio, Jon, and others, Alex 
> and I have produced a specification for ARM blocks that is much closer 
> to Java Language Specification (JLS) style and rigor. The specification 
> involves changes to the existing JLS section 14.20 "The try statement," 
> and will eventually introduce a new subsection 14.20.3 "Execution of 
> try-with-resources," although the specification below is not partitioned 
> as such. Non-normative comments about the specification text below 
> appear inside "[]". Differences between the new specification and the 
> earlier Project Coin proposal for ARM are discussed after the specification.
>
>
>   

[snip]

> * Adjustments to the suppressed exception logic: in the present 
> specification, an incoming primary exception will suppress an Exception 
> thrown by a close method; however, if the close method throws an error, 
> that error is propagated out without suppressing an incoming primary 
> exception. Possible alternatives include having a primary exception in a 
> try-with-resource statement suppress all subsequent Throwables 
> originating in the statement and having a non-Exception thrown by a 
> close suppress any incoming primary exception.
>
> These alternatives could be implemented by replacing the translated code
>
>               try {
>                 #resource.close();
>               } catch(Exception #suppressedException) {
>                 
> #primaryException.addSuppressedException(#suppressedException);
>               }
>
> with
>
>               try {
>                 #resource.close();
>               } catch(Throwable #suppressedException) {
>                 
> #primaryException.addSuppressedException(#suppressedException);
>               }
>
> or
>
>               try {
>                 #resource.close();
>               } catch(Exception #suppressedException) {
>                 
> #primaryException.addSuppressedException(#suppressedException);
>               } catch(Throwable #throwable) {
>                 #throwable.addSuppressedException(#primaryException);
>                 throw #throwable;
>               }
>
> respectively.
>
> -Joe
>   

We've decided to change the specification to the first alternative, 
where an incoming primary suppresses all Throwables rather than just 
subclasses of java.lang.Exception.

The initial code push [1] actually implemented those semantics; a test 
has been added to verify the newly specified behavior [2].

-Joe

[1] http://hg.openjdk.java.net/jdk7/tl/langtools/rev/13354e1abba7
[2] http://hg.openjdk.java.net/jdk7/tl/langtools/rev/38e2c23309f1