RFR: 8263614: javac allows local variables to be accessed from a static context

[Vicente Romero]

On Wed, 12 May 2021 20:37:04 GMT, Vicente Romero <vromero at openjdk.org> wrote:

> javac breaks with NPE if compiles this code:
> 
> 
> public class LocalClasses {
>     public static void main(String[] args) {
>         int i = 5;
>         class Local {
>             static void m() {
>                 System.out.println("Value of i = " + i);
>             }
>         }
>         Local.m();
>     }
> } 
> 
> 
> actually the compiler should issue a compiling error as local variable `i` is being accessed from a static context. Please review this fix to address this issue. Some notes:
> 
> `com.sun.tools.javac.comp.AttrContext.staticLevel` keeps a the number of nested static contexts but this calculation doesn't consider static type declarations. This is because static declaration doesn't introduce a static context. But if they have a static modifier, even if implicit as it is for local records, then this affects what variables, type variables, etc are accessible from the body of the static type declaration. For this reason I have used an `adjusted` static level that takes static type declarations into account.
> 
> TIA

thanks Maurizio for taking the time to dig deeper into this issue. Your patch is elegant but we will need some additional changes if we decide to go through that path, for example the compiler is accepting this code with your patch instead of issuing an error:


class C<T> {
    int field = 0;
    <U> void foo(int param) {
        int localVar = 1;
        class Local {
            static void m() {
                U u;
            }
        }
    }
}

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

PR: https://git.openjdk.java.net/jdk/pull/4004