RFR: 8325859: potential information loss during type inference [v3]

[Maurizio Cimadamore]

On Fri, 2 May 2025 20:28:06 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> When an inference context (`IC`) is minimized, the minimized inference context (`MIC`) contains a proper subset of `IC's` inference vars (`IC_IV`). In other words there will be at least one inference variable `T` that belongs to `IC_IV` which doesn't belong to the minimized context inference variable's set (`MIC_IV`). MIC can be propagated to another inference context (AIC) as part of the type inference algo. If at any moment a type containing `T` needs, for example, to be instantiated `AIC` won't be able to perform that operation as it lacks the information to realize that `T` is a free variable it was supposed to know about hadn't a minimization step been performed. This PR is proposing to fix this issue without reducing the universe of inference contexts we apply the minimization algo to.
>> 
>> We are basically proposing to add a field to class InferenceContext which will be supplementary inference context that can be used to look for additional information if necessary. Also when registering a free type listener to an inference context, it could be that it won't be registered in the inference context the client could expect but in a supplementary inference context if it is found out that it contains and instantiation to all the free variables related to the listener. See also some comments inlined in the code,
>> 
>> TIA
>
> Vicente Romero has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8325859
>  - make visitor static
>  - updating doc
>  - 8325859: potential information loss during type inference

The way this was designed, IIRC, was that if MIC is derived from IC, every time a variable is inferred in MIC, the resolution is forwarded to all the equivalent type variables in IC. If there's more type-variables in IC that are neither contained in MIC, nor equivalent to another var contained in MIC, it seems like an issue, as the minimization algo is not designed to work in this way.

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PR Comment: https://git.openjdk.org/jdk/pull/25011#issuecomment-2866734687