Suppress warnings in comprehensions with 22+ binds #23590
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Fixes scala#23164 At that point, we emit a TupleXXL pattern case bundling all the variable bindings so far. The type tests in these patterns cannot be checked at runtime due to erasure. But we know these are safe, so we mark them as `@unchecked`.
| makeCaseLambda(CaseDef(gen.pat, EmptyTree, body) :: Nil, matchCheckMode) | ||
| val pat = gen.pat.match | ||
| case Tuple(pats) if pats.length > Definitions.MaxImplementedFunctionArity => | ||
| /* The pattern case is a tupleXXL, because we have bound > 21 variables in the comprehension. |
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| /* The pattern case is a tupleXXL, because we have bound > 21 variables in the comprehension. | |
| /* The pattern case is a tupleXXL, because we have bound > 22 variables in the comprehension. |
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Depends on how you look at it. If the source program has > 21 binds, then we'll get the TupleXXL. For <= 21 we won't. The tuple in the pattern case being generated here will always carry one variable more.
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There exists a Tuple22 class: https://dotty.epfl.ch/api/scala/Tuple22.html#
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The rule is if we have n binds, then the generated case will destructure a tuple of length n + 1. The example in the issue has 22, which is > 21, ergo we will match on a 23 tuple and get a TupleXXL.
| /* The pattern case is a tupleXXL, because we have bound > 21 variables in the comprehension. | ||
| * In this case, we need to mark all the typed patterns as @unchecked, or get loads of warnings. | ||
| * Cf. warn test i23164.scala */ | ||
| Tuple: |
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Would just annotating the whole pattern work?
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I'm not sure. Before this PR, the generated case would look like
val xxl = scala.runtime.TupleXXL(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23)
(xxl: @unchecked).match // <- @unchecked inserted here
case scala.runtime.TupleXXL(a1,a2,a3,a4,a5,a6:List[Int],a7,a8,a9,a10,a11,a12,a13,a14,a15,a16,a17,a18,a19,a20,a21,a22,a23) => true
// ^ gives a warning
case _ => falseI'm unable to surround the whole scala.runtime.TupleXXL(a1,a2,...) with @unchecked and get it to compile.
Edit: Also, surrounding the entire match with @unchecked does not suppress the warning for the :List[Int] type test.
Fixes #23164
At that point, we emit a TupleXXL pattern case bundling all the variable bindings so far. The type tests in these patterns cannot be checked at runtime due to erasure. But we know these are safe, so we mark them as
@unchecked.