RFR: 8194743: Compiler implementation for Statements before super() [v16]

[Archie Cobbs]

On Mon, 25 Sep 2023 17:31:57 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Should this work?
>> 
>> class Test {
>>     String s = "Hello";
>> 
>>     void m() {
>>         System.out.println("Hello");
>>     }
>> 
>>     class Inner {
>>         Inner() {
>>             m();
>>             super();
>>         }
>>     }
>> 
>>     public static void main(String[] args) {
>>         new Test().new Inner();
>>     }
>> }
>> 
>> The proposed changes accept this program. But I can't find supporting text in the JLS changes:
>> https://cr.openjdk.org/~gbierman/jep447/jep447-20230620/specs/statements-before-super-jls.html
>
> After some internal discussion, it is good for javac to accept this, as this case can be supported using the `this$0` parameter that is passed into the constructor of `Inner` (no `this` reference is strictly required). But the JLS text supporting this seems ambiguous:
> 
> 
> The pre-construction context includes the prologue of the constructor 8.8.7 and the explicit constructor invocation itself. Within a pre-construction context, constructs that refer explicitly or implicitly to the current object are disallowed.
> 
> 
> It is not clear to me as to whether `m()` refers to the current object or not - as it seems one would have to have intimate knowledge of how the compiler translates the code in order to answer that question.

> where does env1 == env come from?

To be honest I can't remember. At some point it was needed to make something compile, but I can't come up with an example anymore (if you can, I'll tell you why it was there :)

The thinking must have been: "It can't possibly matter if the AST 'cursor'  is in the pre-construction context of an outer instance class; it only matters if we are in the pre-construction context of the class under construction."

> The proposed changes accept this program. But I can't find supporting text in the JLS changes

The spec is still being finalized ([here's the latest version](https://cr.openjdk.org/~gbierman/jep447/jep447-20230905/specs/statements-before-super-jls.html#jls-8.8)). The newer §15.12.3 should allow this.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13656#discussion_r1336237288