Merge pull request #9605 from 7mind/parse-variant-underscore-placehol…

…ders

Parse `+_` and `-_` in types as identifiers to support Scala 3.2 placeholder syntax

src/compiler/scala/tools/nsc/ast/parser/Parsers.scala

@@ -1139,11 +1139,16 @@ self =>
               else
                 atPos(start)(makeSafeTupleType(inParens(types())))
             case _      =>
-              if (isWildcardType) {
+              if (settings.isScala3 && (in.name == raw.PLUS || in.name == raw.MINUS) && lookingAhead(in.token == USCORE)) {
+                val start = in.offset
+                val identName = in.name.encode.append("_").toTypeName
+                in.nextToken()
+                in.nextToken()
+                atPos(start)(Ident(identName))
+              } else if (isWildcardType) {
                 val scala3Wildcard = isScala3WildcardType
                 wildcardType(in.skipToken(), scala3Wildcard)
-              }
-              else
+              } else
                 path(thisOK = false, typeOK = true) match {
                   case r @ SingletonTypeTree(_) => r
                   case r => convertToTypeId(r)

test/files/neg/variant-placeholders-future.check

@@ -0,0 +1,7 @@
+variant-placeholders-future.scala:4: error: `=`, `>:`, or `<:` expected
+  type -_ = Int // error -_ not allowed as a type def name without backticks
+        ^
+variant-placeholders-future.scala:5: error: `=`, `>:`, or `<:` expected
+  type +_ = Int // error +_ not allowed as a type def name without backticks
+        ^
+2 errors

test/files/neg/variant-placeholders-future.scala

@@ -0,0 +1,6 @@
+// scalac: -Xsource:3
+//
+object Test {
+  type -_ = Int // error -_ not allowed as a type def name without backticks
+  type +_ = Int // error +_ not allowed as a type def name without backticks
+}

test/files/neg/variant-placeholders-nofuture.check

@@ -0,0 +1,7 @@
+variant-placeholders-nofuture.scala:5: error: ';' expected but '_' found.
+  val fnMinusPlus1: -_ => +_ = (_: Int).toLong // error -_/+_ won't parse without -Xsource:3
+                     ^
+variant-placeholders-nofuture.scala:6: error: ')' expected but '_' found.
+  val fnMinusPlus2: (-_) => +_ = fnMinusPlus1  // error -_/+_ won't parse without -Xsource:3
+                      ^
+2 errors

test/files/neg/variant-placeholders-nofuture.scala

@@ -0,0 +1,8 @@
+object Test {
+  type `-_` = Int
+  type `+_` = Long
+
+  val fnMinusPlus1: -_ => +_ = (_: Int).toLong // error -_/+_ won't parse without -Xsource:3
+  val fnMinusPlus2: (-_) => +_ = fnMinusPlus1  // error -_/+_ won't parse without -Xsource:3
+  val fnMinusPlus3: -_ => (+_) = fnMinusPlus2  // error -_/+_ won't parse without -Xsource:3
+}

test/files/pos/variant-placeholders-future.scala

@@ -0,0 +1,35 @@
+// scalac: -Xsource:3
+//
+object Test {
+  type `-_` = Int
+  type `+_` = Long
+
+  val fnMinusPlus1: -_ => +_ = (_: Int).toLong
+  val fnMinusPlus2: (-_) => +_ = fnMinusPlus1
+  val fnMinusPlus3: -_ => (+_) = fnMinusPlus2
+
+  val fnTupMinusPlus2: (=> -_, -_) => +_ = (a, b) => ((a: Int) + (b: Int)).toLong
+  def defMinusPlus2(byname: => -_, vararg: -_*): +_ = ((vararg.sum: Int) + (byname: -_)).toLong
+  val infixMinusPlus2: -_ Either +_ = Right[-_, +_](1L)
+
+  val optPlus: Option[+_] = Some[ + _ ](1L)  // spaces allowed
+  optPlus match {
+    case opt: Option[ + _ ] =>
+      val opt1: + _ = opt.get
+      val opt2: Long = opt1
+  }
+
+  val optMinus: Option[-_] = Some[ - _ ](1)  // spaces allowed
+  optMinus match {
+    case opt: Option[ - _ ] =>
+      val opt1: `-_` = opt.get
+      val optErr: - _ = opt.get
+      val opt2: Int = opt1
+  }
+
+  locally {
+    type `-_`[A] = A
+    type `+_`[A] = Option[A]
+    val optOpt: Option[ + _ [+_[-_[Int]]]] = Some(Some(Some(1)))
+  }
+}