allow nullability flow typing even in presence of pattern match #18206
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olhotak force-pushed the fix-match-flow-typing branch from bae1d8f to f0b9af5 Compare 
| I'd like test this PR after #18212 is merged. var s: String | Null = ??? s match case null => s = "" case _ => val ss: String = sWill this work? |
Nullability flow typing is conservatively disabled for mutable variables to which a write occurs nested inside a Tree other than some known ones, such as If and WhileDo. This is to prevent flow-sensitive reasoning for variables that are captured and written to in a closure. Pattern matches do not create a closure. This change enables nullability flow typing even for mutable variables that are written to inside a pattern match.
olhotak force-pushed the fix-match-flow-typing branch from f0b9af5 to f351ec4 Compare 
| It should be possible to also do this for |
odersky approved these changes Oct 1, 2023
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Nullability flow typing is conservatively disabled for mutable variables to which a write occurs nested inside a Tree other than some known ones, such as If and WhileDo. This is to prevent flow-sensitive reasoning for variables that are captured and written to in a closure. Pattern matches do not create a closure. This change enables nullability flow typing even for mutable variables that are written to inside a pattern match.