RFR: 8367530: The exhaustiveness errors could be improved [v13]

[Jan Lahoda]

On Mon, 26 Jan 2026 12:21:49 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Also, `isBpCovered` seems to be called by routines (like `reduceRecordPattern`) that do not seem related to the new logic (which is what got me suspicious about the location of the update to begin with). Which has (at least in theory) potential for `TooManyChecksException` to trigger in places where it's not expected? (but maybe that's handled by the special value `-1` which is carefully set after the new logic runs)
>
> A possible suggestion might be to add this check inside `doExpandMissingPatternDescriptions` -- after the `if (toExpand instanceof BindingPattern bp) {` ?

I've renamed the method. I also tried to put the check it on some other places; but unfortunately I couldn't find a better place where setting a sensible value (i.e. such that would not cancel tests in `ExhaustivenessConvenientErrors.java`, but would cancel `Exhaustiveness.testDeeplyNestedNotExhaustive`). 

Yes, during the "real" run, `baseChecks` should be `-`, and that should prevent the cancelation from happening.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27256#discussion_r2732893680