Escape this analysis does not consider anonymous class/local class

[Archie Cobbs]

Hi Remi,

On Mon, Oct 2, 2023 at 2:18 AM Remi Forax <forax at univ-mlv.fr> wrote:

> The compiler does not emit a warning when the access to "this" is buried
> inside an anonymous class
>

This is a known limitation. In summary, the analyzer tracks 'this'
references that are outer instance references from the current instance,
but it doesn't track 'this' references that are outer instance references
from arbitrary objects on the stack.

So when you say "new Inner()", the analyzer doesn't track the fact that the
object on top of the stack now has a 'this' reference via its outer
instance.

This is one of the (many) trade-offs that were made between precision vs.
code complexity.

There are a couple of possible ways to address this:

   1. Using existing reference types: record "new Inner()" as having an
   indirect 'this' reference, and then update the logic for "Outer.this" to
   pessimistically assume any indirect reference is an outer reference.
   2. Add a new reference type: OuterExprRef to mean "a 'this' reference
   from the outer instance of the object on the stack" and add tracking for it

Option #1 would probably lead to a bunch of new false positives. Option #2
is more precise and therefore better but requires more code.

-Archie

-- 
Archie L. Cobbs
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