Improve missing pattern suggestions for empty case expressions with multiple subjects
#3.569 geöffnet am 27. Aug. 2024
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Beschreibung
When there is a case expression with no matched patterns, we attempt to improve the error by running the first column through exhaustiveness checking (See #3561, here).
This works fine, for example, matching on values of type Bool, Result(_, _) suggest True, _ and False, _.
This could be improved to suggest all four possible patterns, although as discussed in the above PR, this grows exponentially, so maybe requires more discussion.
But one way it could definitely be improved is the following:
When matching on values of type, for example, Int, Bool, where the first type has infinite patterns, it only suggests _, _, since only the first subject is checked.
My suggestion for this is to do checking for all subjects, but cap the maximum number of paths, at say 64, so we don't end up emitting thousands of missing patterns. (Rust Analyzer does this, though I don't remember what the number is). That way we get good suggestions without overrunning the user with too many patterns.