RFR: 8282274: Compiler implementation for Pattern Matching for switch (Third Preview) [v6]

[Jan Lahoda]

> This is a (preliminary) patch for javac implementation for the third preview of pattern matching for switch (type patterns in switches).
> 
> Draft JLS:
> http://cr.openjdk.java.net/~gbierman/PatternSwitchPlusRecordPatterns/PatternSwitchPlusRecordPatterns-20220407/specs/patterns-switch-jls.html
> 
> The changes are:
> -there are no guarded patterns anymore, guards are not bound to the CaseElement (JLS 15.28)
> -a new contextual keyword `when` is used to add a guard, instead of `&&`
> -`null` selector value is handled on switch level (if a switch has `case null`, it is used, otherwise a NPE is thrown), rather than on pattern matching level.
> -total patterns are allowed in `instanceof`
> -`java.lang.MatchException` is added for the case where a switch is exhaustive (due to sealed types) at compile-time, but not at runtime.
> 
> Feedback is welcome!
> 
> Thanks!

Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:

  Cleanup, fixing tests.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8182/files
  - new: https://git.openjdk.java.net/jdk/pull/8182/files/dc001541..76f2d05c

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8182&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8182&range=04-05

  Stats: 6 lines in 4 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8182.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8182/head:pull/8182

PR: https://git.openjdk.java.net/jdk/pull/8182