Disallow opaque type aliases of context functions #16041
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We could allow them but they would not do what one probably expects (i.e. create context closures). This is because abstract types upper-bounded by context functions don't do that either (see neg/i16035a.scala), and we have to keep semantic equivalence between the two. Therefore, it's better to disallow them. Fixes scala#16035
som-snytt
reviewed
Sep 14, 2022
| def recur(tp: Type): Unit = tp.dealias match | ||
| case tp: HKTypeLambda => recur(tp.resType) | ||
| case tp if defn.isContextFunctionType(tp) => | ||
| report.error(em"context functon type cannot have opaque aliases", tree.srcPos) |
som-snytt
reviewed
Sep 14, 2022
| @@ -1460,6 +1460,15 @@ trait Checking { | |||
| |CanThrow capabilities can only be generated $req.""", | |||
| pat.srcPos) | |||
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| /** Check that tree does not define a context fucntion type */ | |||
Kordyjan
approved these changes
Sep 15, 2022
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We could allow them but they would not do what one probably expects (i.e. create context closures). This is because abstract types upper-bounded by context functions don't do that either (see neg/i16035a.scala), and we have to keep semantic equivalence between the two.
Therefore, it's better to disallow them.
Fixes #16035