RFR: 8325859: Potential information loss during type inference [v9]

[Vicente Romero]

On Tue, 20 May 2025 14:35:04 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 incrementally with one additional commit since the last revision:
> 
>   updating IC::toString

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/InferenceContext.java line 575:

> 573:                "Undet vars: " + undetvars + '\n';
> 574:         if (parentIC != null) {
> 575:             result += "\nParent : " + parentIC.toString();

I was thinking about using an indentation, probably with a toString overload, but if the chain of parents gets long then one will need to scroll to the sides to see them all

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PR Review Comment: https://git.openjdk.org/jdk/pull/25011#discussion_r2098147323