RFR: 8335766: Switch case with pattern matching and guard clause compiles inconsistently

[Jan Lahoda]

When javac parser see a `case` label, it needs to disambiguate between expressions (constant labels) and patterns. But, for code like:

case R(int x) when (x > 0)


the parser will try to parse the label as an expression, which is obviously not correct. The problem is that it does not disambiguate before `when`, and there indeed is an expression after `when`.

The proposal is to disambiguate as a pattern once there is `when` after a closing parenthesis at the top-level. This should prevent the code to even look at the `when` expression

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Commit messages:
 - 8335766: Switch case with pattern matching and guard clause compiles inconsistently

Changes: https://git.openjdk.org/jdk/pull/20093/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20093&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335766
  Stats: 14 lines in 2 files changed: 12 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/20093.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20093/head:pull/20093

PR: https://git.openjdk.org/jdk/pull/20093