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Fix #4999: allow pattern matching against by-name arguments #5012

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Merged
merged 2 commits into from
Sep 5, 2018
Merged

Fix #4999: allow pattern matching against by-name arguments #5012

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3cc4837
Fix #4999: allow pattern matching against by-name arguments
Blaisorblade Aug 24, 2018
bfb716f
Don't widen stable scrutinee types
Blaisorblade Aug 24, 2018
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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/transform/PatternMatcher.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -116,7 +116,7 @@ object PatternMatcher {
/** Widen type as far as necessary so that it does not refer to a pattern-
* generated variable.
*/
private def sanitize(tp: Type): Type = tp.widenExpr match {
private def sanitize(tp: Type): Type = tp.widenIfUnstable match {
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There is also widenTermRefExpr that seems to work here. Not sure which one is the most appropriate one. I defer to @odersky or @smarter

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Yeah the first commit uses widenTermRefExpr. Maybe @liufengyun can think of examples where widening singletons would make a difference?

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What about x match { case _: x.type => ... } ?

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We concluded with @smarter that there is no need to widen singleton types

case tp: TermRef if refersToInternal(false, tp) => sanitize(tp.underlying)
case tp => tp
}
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9 changes: 9 additions & 0 deletions tests/pos/i4999.scala
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@@ -0,0 +1,9 @@
trait Foo
final class Bar extends Foo

class Test {
def test(xs: => Foo) = xs match {
case xs: Bar => 1
case _ => 2
}
}