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Prevent deprecation of _ in type patterns #18847

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Prevent deprecation of _ in type patterns #18847

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5a47c53
Prevent deprecation of `_` in type patterns
ausmarton Nov 4, 2023
ec18b3b
Remove deprecation warnings from existing tests.
ausmarton Nov 5, 2023
daf661a
Revert test case for deprecation of _ in wildcard arguments
ausmarton Nov 5, 2023
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3 changes: 0 additions & 3 deletions compiler/src/dotty/tools/dotc/parsing/Parsers.scala
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Expand Up @@ -1860,9 +1860,6 @@ object Parsers {
val start = in.skipToken()
Ident(tpnme.USCOREkw).withSpan(Span(start, in.lastOffset, start))
else
if sourceVersion.isAtLeast(future) then
deprecationWarning(em"`_` is deprecated for wildcard arguments of types: use `?` instead")
patch(source, Span(in.offset, in.offset + 1), "?")
val start = in.skipToken()
typeBounds().withSpan(Span(start, in.lastOffset, start))
// Allow symbols -_ and +_ through for compatibility with code written using kind-projector in Scala 3 underscore mode.
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7 changes: 1 addition & 6 deletions compiler/test-resources/repl/i13208.scala
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@@ -1,8 +1,3 @@
//> using options -source:future -deprecation
scala> type M[X] = X match { case Int => String case _ => Int }
scala> type N[X] = X match { case List[_] => Int }
1 warning found
-- Deprecation Warning: --------------------------------------------------------
1 | type N[X] = X match { case List[_] => Int }
| ^
| `_` is deprecated for wildcard arguments of types: use `?` instead
scala> type N[X] = X match { case List[_] => Int }
1 change: 0 additions & 1 deletion sbt-test/compilerReporter/i14576/Test.scala
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Expand Up @@ -13,5 +13,4 @@ object Test:
// private[this] and = _ are deprecated under -source:future
private[this] var x: AnyRef = _

// under -source:future, `_` is deprecated for wildcard arguments of types: use `?` instead
val xs: List[_] = Nil
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This change does not seem right. In that position, List[_] is not a pattern type, so _ should stay deprecated.

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Thanks very much, I've removed the change to the test now. The fix isn't as trivial as I thought it was.

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Currently this warining is not properly tested for cases that are not in patterns. I am adding tests in #18813.

2 changes: 1 addition & 1 deletion sbt-test/compilerReporter/i14576/build.sbt
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Expand Up @@ -24,7 +24,7 @@ lazy val root = (project in file("."))
},
assertDeprecationSummary := {
assert {
FakePrintWriter.messages.exists(_.contains("there were 3 deprecation warnings; re-run with -deprecation for details"))
FakePrintWriter.messages.exists(_.contains("there were 2 deprecation warnings; re-run with -deprecation for details"))
}
},
assertNoDeprecationSummary := {
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3 changes: 0 additions & 3 deletions tests/pos-with-compiler-cc/dotc/parsing/Parsers.scala
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Expand Up @@ -1730,9 +1730,6 @@ object Parsers {
val start = in.skipToken()
Ident(tpnme.USCOREkw).withSpan(Span(start, in.lastOffset, start))
else
if sourceVersion.isAtLeast(future) then
deprecationWarning(em"`_` is deprecated for wildcard arguments of types: use `?` instead")
patch(source, Span(in.offset, in.offset + 1), "?")
val start = in.skipToken()
typeBounds().withSpan(Span(start, in.lastOffset, start))
// Allow symbols -_ and +_ through for compatibility with code written using kind-projector in Scala 3 underscore mode.
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8 changes: 8 additions & 0 deletions tests/pos/i18808.scala
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@@ -0,0 +1,8 @@
//> using options -Werror
import language.future

type F[X] = X match
case List[_] => Int

type G[X] = X match
case List[?] => Int
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