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

[Jan Lahoda]

> 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.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21495/files
  - new: https://git.openjdk.org/jdk/pull/21495/files/7bf21b9c..e2d5f105

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21495&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21495&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21495.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21495/head:pull/21495

PR: https://git.openjdk.org/jdk/pull/21495