RFR: 8287236: Reorganize AST related to pattern matching for switch [v3]

[Maurizio Cimadamore]

On Thu, 2 Jun 2022 10:55:44 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Under JEP 427, case label elements may be: a) expressions; b) patterns; c) the default. Currently, this is modeled in the Trees API in a way where all expressions and patterns extend `CaseLabelTree`.
>> 
>> When guarded patterns were removed in favor of guards on pattern case label element, it was necessary to augment all patterns with a guard, which is only used when the pattern is used as a case label element. This is somewhat inconsistent for the Trees API.
>> 
>> A use a layer of indirection is proposed here: - the `CaseLabelTree` has three subtypes: `ConstantCaseLabelTree`, which contains `ExpressionTree` as a subnode; `PatternCaseLabelTree`, which contains `PatternTree` and a guard (`ExpressionTree`) as subnodes; and the `DefaultCaseLabelTree` for the default clause.
>> 
>> This patch also fixes `TreeScanner.visitCase`, which currently iterates only over `CaseTree.getExpressions()`, ignoring patterns. It is changed to iterate over `CaseTree.getLabels()`, to get all labels.
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Reflecting review comments.

Looks good

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

Marked as reviewed by mcimadamore (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/8959