RFR: 8263614: javac allows local variables to be accessed from a static context [v2]

[Maurizio Cimadamore]

On Thu, 13 May 2021 20:37:37 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
>
> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update after review comments

I'm doing more investigation. The code for resolving types is definitively complex. It seems to me that the complexity comes from 3 problems:

Problem 1:


class Foo<T> {
static T t;
}


Here the env for `t` has ` scope which can see T.

Problem 2:


class Foo<T> {
static void m() {
   T t;
}
}


Here the env for `m` has ` scope which can see T.

Problem 3:


class Foo {
static <Z> void m() {
   Z z;
}
}


This should obviously work, although, in compiler terms, there's not much difference between (3) and (2).

I'm currently looking into all the changes made in this area in recent times, and see if there's an easier path to support all this.

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

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