Javac and local records capturing

[Brian Goetz]

I agree it should be rejected.  We found a similar example and are 
looking into how this should be specified, as "local static" constructs 
are a new thing.

On 12/24/2019 4:45 AM, Tagir Valeev wrote:
> Hello!
>
> I'm playing with javac 14-ea+28-1366 and local records. Looks like it
> doesn't prevent capturing of outer context. E.g.:
>
> class X {
>    public static void main(String[] args) {
>      int x = 2;
>      record Y() {
>        void test() {
>          System.out.println(x);
>        }
>      }
>      new Y().test();
>    }
> }
>
> javac happily compiles this program and it prints 2. I think it should
> be rejected as it captures a local variable from the outer context.
>
> Also, it looks like capturing compile-time constant should be ok. E.g.
> if we add `final ` before `int x = 2`, then it should be accepted.
> Unfortunately spec draft is silent about whether it's ok to capture
> compile-time constant local variable in the record.
>
> Finally, this code breaks the compiler:
>
> class X {
>    public static void main(String[] args) {
>      int x = 2;
>      record Y() {
>        static final int y = x;
>      }
>      new Y();
>    }
> }
>
> Javac output is the following:
>
> Note: Test.java uses preview language features.
> Note: Recompile with -Xlint:preview for details.
> An exception has occurred in the compiler (14-ea). Please file a bug
> against the Java compiler via the Java bug reporting page
> (http://bugreport.java.com) after checking the Bug Database
> (http://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.NullPointerException
>          at jdk.compiler/com.sun.tools.javac.jvm.Code.emitop0(Code.java:568)
>          at jdk.compiler/com.sun.tools.javac.jvm.Items$SelfItem.load(Items.java:369)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitIdent(Gen.java:2257)
>          at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:2411)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:864)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitAssign(Gen.java:1998)
>          at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCAssign.accept(JCTree.java:1981)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genExpr(Gen.java:864)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitExec(Gen.java:1723)
>          at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1524)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:597)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:632)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:618)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStats(Gen.java:669)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitBlock(Gen.java:1084)
>          at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1039)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:597)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genStat(Gen.java:632)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genMethod(Gen.java:954)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitMethodDef(Gen.java:917)
>          at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:885)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genDef(Gen.java:597)
>          at jdk.compiler/com.sun.tools.javac.jvm.Gen.genClass(Gen.java:2395)
>          at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.genCode(JavaCompiler.java:756)
>          at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1646)
>          at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.generate(JavaCompiler.java:1614)
>          at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:972)
>          at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:316)
>          at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:176)
>          at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:57)
>          at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:43)
>
> With best regards,
> Tagir Valeev