RFR: 8341901: Using 'var' keyword switch pattern matching causes compiler error [v2]

[Vicente Romero]

On Fri, 15 Nov 2024 11:08:38 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Consider code like:
>> 
>> public class T {
>>    record R(N.I i) {}
>>    int test(Object o) {
>>        return switch (o) {
>>            case R(var nested) -> 0;
>>            default -> 0;
>>        };
>>    }
>>    static class N<T> {
>>        interface I {}
>>    }
>> }
>> 
>> 
>> This fails to compile since JDK 23, due to:
>> 
>> $ javac T.java 
>> error: cannot select a static class from a parameterized type
>> 1 error
>> 
>> 
>> The reason for the error is this: the type of `nested` is inferred to `T.N.I`. This is correct. javac will then construct a synthetic AST for it, and the AST will be structurally correct as well: `T.N.I`. But a) the `Type` attached to `T.N` will be `T.N<T>` (which by itself is not correct), and b) after the synthetic AST is created, `Check.validate` is called on the type's AST, and fails, as the types is sees correspond to `T.N<T>.I`, which is illegal.
>> 
>> Note the synthetic AST is also set for local variable type inference, but the `validate` is called *before* the synthetic AST is created.
>> 
>> This PR proposes to do two things:
>> - move the `validate` call before the synthetic AST creation for `visitBindingPattern`, to mimic the behavior for `var`s.
>> - the `TreeMaker` is tweaked to inject erased types instead of parameterized types when generating qualified identifiers for classes or interfaces. This should correspond more closely to what happens when one types `T.N.I` in the source code.
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adding a comment specifying the type that's used to attribute the QualIdent is a raw type.

lgtm

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

Marked as reviewed by vromero (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21495#pullrequestreview-2439527264