Double-semicolon in import statements

[Alex Buckley]

Oh, I wouldn't assume a _lot_ of code has stray semicolons, in either 
relative or absolute terms. But if it's prevalent at one company (bad 
Perl script or whatever), then the bug report about how they moved to 
JDK8 and their code stopped compiling will have more force.

Anyway, it's good to know that Eclipse-written code doesn't have stray 
semicolons. That certainly tips the scale back towards changing javac.

Of course a clean solution would be to remove the ability to use ; as a 
type declaration. It's as obsolescent in 2013 as the ability to place [] 
after the formal parameter section of a method declaration (JLS 8.4). It 
would be interesting to know, Jeremy, if either ;-as-type-declaration or 
[]-after-parameters occurs in your codebase.

Alex

On 8/2/2013 5:01 PM, Jeremy Manson wrote:
> That was why I asked - my assumption was that something like this is
> going to be present in a *lot* of Java code, which would then need to be
> fixed.
>
> OTOH, Martin and I just searched a very large code base, and there were
> a vanishingly small number of these (this may be because eclipse treats
> the double semicolon as an error).  There were far, far more instances
> of classes that of accessed the private fields of superclasses.  Also,
> it doesn't seem to be present in any JDK code. Perhaps it isn't as big a
> problem as one might imagine.
>
> Jeremy
>
>
> On Fri, Aug 2, 2013 at 4:07 PM, Alex Buckley <alex.buckley at oracle.com
> <mailto:alex.buckley at oracle.com>> wrote:
>
>     Another factor in determining whether to change the JLS or javac is
>     the extent of the mis-implementation.
>
>     Here's an example. Jeremy had the insight to try an extra semicolon
>     after an import declaration other than the last one, and javac
>     accepted it. Suppose he'd also tried an extra semicolon after the
>     package declaration, and that javac accepted it too. We would then
>     have to accept that real-world code probably has more stray
>     semicolons than we imagined, since javac has been allowing them all
>     this time. That makes it harder to change javac to ban them, since
>     it would spark a round of bug reports that have no good outcome for
>     anyone. And so, I'd be more inclined than usual to change the JLS to
>     accommodate javac.
>
>     Sadly, as of JDK8b98, I can report that javac accepts extra
>     semicolons after the package declaration. I would be interested in
>     other locations anyone might find, but right now, it's looking like
>     JLS 7.3 will have to change.
>
>     Alex
>
>
>     On 8/2/2013 2:04 PM, Jonathan Gibbons wrote:
>
>         True,
>
>         FWIW, if we change javac such that the set of programs accepted
>         by javac
>         is changed, we have an process (currently Oracle internal) to get
>         approval for such a change.   So, we would not simply change
>         javac on a
>         whim to meet the spec; we would at least have other eyes looking
>         at the
>         behavioral change to determine if it is "acceptable".
>
>         -- Jon
>
>
>         On 08/02/2013 02:00 PM, John Spicer wrote:
>
>
>             On Aug 2, 2013, at 4:45 PM, Jonathan Gibbons
>             <jonathan.gibbons at oracle.com
>             <mailto:jonathan.gibbons at oracle.com>
>             <mailto:jonathan.gibbons at __oracle.com
>             <mailto:jonathan.gibbons at oracle.com>>> wrote:
>
>                 In general, it is better/simpler to change javac to
>                 conform to the
>                 spec. (Except when it is not.)
>
>
>             Well, you sure can't argue with that statement  :-)
>
>             It is unfortunate that, in the example given, if the user
>             swaps what
>             look like import declarations with a redundant semicolon the
>             code
>             changes from being invalid to valid (or vice-versa if the
>             code began
>             in the other sequence).
>
>             John.
>
>
>                 -- Jon
>
>                 On 08/02/2013 11:36 AM, Jeremy Manson wrote:
>
>                     Just out of my own curiosity, who decides whether to
>                     change the spec
>                     or javac?
>
>                     Jeremy
>
>
>                     On Fri, Aug 2, 2013 at 10:25 AM, John Spicer
>                     <jhs at edg.com <mailto:jhs at edg.com>
>                     <mailto:jhs at edg.com <mailto:jhs at edg.com>>> wrote:
>
>
>                          On Aug 2, 2013, at 12:57 PM, Alex Buckley
>                          <alex.buckley at oracle.com
>                     <mailto:alex.buckley at oracle.com>
>                     <mailto:alex.buckley at oracle.__com
>                     <mailto:alex.buckley at oracle.com>>> wrote:
>
>                          > Nope, the production is:
>                          >
>                          > CompilationUnit:
>                          >  PackageDeclarationopt ImportDeclarationsopt
>                     TypeDeclarationsopt
>                          >
>                          > So that's a javac bug. (And a reason for
>                     minimizing undue
>                          flexibility in the language in the first place.)
>
>                          I'm generally happier to ban things like extra
>                     semicolons, but
>                          it seems to me that "import x.y;;" should be
>                     allowed regardless
>                          of what follows.
>
>                          FWIW, out front end does give the appropriate
>                     error, the rules
>                          just seem odd to me.
>
>                          John.
>
>                          >
>                          > Alex
>                          >
>                          > On 8/1/2013 12:59 PM, Jeremy Manson wrote:
>                          >> Alex,
>                          >>
>                          >> What about the following, which also
>                     compiles?  Can you
>                          >> have ImportDeclaration TypeDeclaration
>                     ImportDeclaration?
>                          >>
>                          >> import java.util.HashMap;;
>                          >> import java.util.LinkedList;
>                          >>
>                          >> public class Semicolon {
>                          >>   public static void main(String[] args) {
>                          >>      System.out.println("This program should
>                     not compile");
>                          >>   }
>                          >> }
>                          >>
>
>
>
>
>
>