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Exhaustivity warnings on nested case classes #13030

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Jul 12, 2021
Merged

Exhaustivity warnings on nested case classes #13030

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13 changes: 7 additions & 6 deletions compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -804,6 +804,8 @@ class SpaceEngine(using Context) extends SpaceLogic {
}

private def exhaustivityCheckable(sel: Tree): Boolean = {
val seen = collection.mutable.Set.empty[Type]

// Possible to check everything, but be compatible with scalac by default
def isCheckable(tp: Type): Boolean =
val tpw = tp.widen.dealias
Expand All @@ -815,16 +817,15 @@ class SpaceEngine(using Context) extends SpaceLogic {
isCheckable(and.tp1) || isCheckable(and.tp2)
}) ||
tpw.isRef(defn.BooleanClass) ||
classSym.isAllOf(JavaEnumTrait)
classSym.isAllOf(JavaEnumTrait) ||
classSym.is(Case) && {
if seen.add(tpw) then productSelectorTypes(tpw, sel.srcPos).exists(isCheckable(_))
else true // recursive case class: return true and other members can still fail the check
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It seems false aligns better with the protocol that if a component is sealed, then perform the check.

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Given something like case class Foo(parent: Option[Foo], other: Bar) this else branch is hit when we've running isCheckable(Foo) on the Foo in the Option. My thinking is we can optimistically return true here, and then whether or not Bar is checkable will determine if the top Foo is checkable. So I think true is right here, no?

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Given the following type:

case class A(a: A)

IIRC, the implementation above will have isCheckable(A) == true. If that's as expected, then true is fine. Otherwise, it seems false should be used here.

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Yeah, I'm happy with that result.

}

val res = !sel.tpe.hasAnnotation(defn.UncheckedAnnot) && {
ctx.settings.YcheckAllPatmat.value
|| isCheckable(sel.tpe)
|| {
val tpw = sel.tpe.widen.dealias
val classSym = tpw.classSymbol
classSym.is(Case) && productSelectorTypes(tpw, sel.srcPos).exists(isCheckable(_))
}
}

debug.println(s"exhaustivity checkable: ${sel.show} = $res")
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13 changes: 9 additions & 4 deletions compiler/test/dotty/tools/dotc/transform/PatmatExhaustivityTest.scala
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Expand Up @@ -15,21 +15,26 @@ import java.nio.file.{Path => JPath}
import scala.io.Source._
import org.junit.Test

class PatmatDefaultExhaustivityTest extends PatmatExhaustivityTest {
override val testsDir = "tests/patmat-default"
override val options = super.options.filter(_ != "-Ycheck-all-patmat")
}

class PatmatExhaustivityTest {
val testsDir = "tests/patmat"
// stop-after: patmatexhaust-huge.scala crash compiler
val options = List("-pagewidth", "80", "-color:never", "-Ystop-after:explicitSelf", "-Ycheck-all-patmat", "-classpath", TestConfiguration.basicClasspath)
def options = List("-pagewidth", "80", "-color:never", "-Ystop-after:explicitSelf", "-Ycheck-all-patmat", "-classpath", TestConfiguration.basicClasspath)

private def compile(files: Seq[String]): Seq[String] = {
val stringBuffer = new StringWriter()
val reporter = TestReporter.simplifiedReporter(new PrintWriter(stringBuffer))
val printWriter = new PrintWriter(stringBuffer)
val reporter = TestReporter.simplifiedReporter(printWriter)

try {
Main.process((options ++ files).toArray, reporter, null)
} catch {
case e: Throwable =>
println(s"Compile $files exception:")
e.printStackTrace()
e.printStackTrace(printWriter)
}

stringBuffer.toString.trim.replaceAll("\\s+\n", "\n") match {
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0 tests/patmat/i12485.scala → tests/patmat-default/i12485.scala
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4 changes: 4 additions & 0 deletions tests/patmat-default/i13003.check
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@@ -0,0 +1,4 @@
4: Pattern Match Exhaustivity: One(Two(None))
7: Pattern Match Exhaustivity: Two(None)
10: Pattern Match Exhaustivity: None, Some(None)
13: Pattern Match Exhaustivity: None, Some(None), Some(Some(None))
14 changes: 14 additions & 0 deletions tests/patmat-default/i13003.scala
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@@ -0,0 +1,14 @@
case class One(two: Two)
case class Two(o: Option[Int])

def matchOneTwo(one: One) = one match
case One(Two(Some(i))) => "match!"

def matchTwo(two: Two) = two match
case Two(Some(i)) => "match!"

def matchOO(oo: Option[Option[Int]]) = oo match
case Some(Some(i)) => "match!"

def matchOOO(ooo: Option[Option[Option[Int]]]) = ooo match
case Some(Some(Some(i))) => "match!"