chore: add scala.language.experimental.unqualifiedSelectors

Author: hamzaremmal

compiler/src/dotty/tools/dotc/config/Feature.scala

@@ -38,6 +38,7 @@ object Feature:
   val quotedPatternsWithPolymorphicFunctions = experimental("quotedPatternsWithPolymorphicFunctions")
   val packageObjectValues = experimental("packageObjectValues")
   val subCases = experimental("subCases")
+  val unqualifiedSelectors = experimental("unqualifiedSelectors")
 
   def experimentalAutoEnableFeatures(using Context): List[TermName] =
     defn.languageExperimentalFeatures
@@ -66,6 +67,7 @@ object Feature:
     (into, "Allow into modifier on parameter types"),
     (modularity, "Enable experimental modularity features"),
     (packageObjectValues, "Enable experimental package objects as values"),
+    (unqualifiedSelectors, "Enable unqualified selectors for expressions and patterns")
   )
 
   // legacy language features from Scala 2 that are no longer supported.

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2802,7 +2802,7 @@ object Parsers {
         case MACRO =>
           val start = in.skipToken()
           MacroTree(simpleExpr(Location.ElseWhere))
-        case DOT =>
+        case DOT if in.featureEnabled(Feature.unqualifiedSelectors)  =>
           accept(DOT)
           selector(EmptyTree)
         case _ =>
@@ -3308,7 +3308,7 @@ object Parsers {
         simpleExpr(Location.InPattern)
       case XMLSTART =>
         xmlLiteralPattern()
-      case DOT =>
+      case DOT if in.featureEnabled(Feature.unqualifiedSelectors) =>
         accept(DOT)
         simplePatternRest(selector(EmptyTree))
       case GIVEN =>

compiler/src/dotty/tools/dotc/parsing/Scanners.scala

@@ -15,6 +15,7 @@ import Tokens.*
 import scala.annotation.{switch, tailrec}
 import scala.collection.mutable
 import scala.collection.immutable.SortedMap
+import scala.collection.immutable.BitSet
 import rewrites.Rewrites.patch
 import config.Feature
 import config.Feature.{migrateTo3, sourceVersion}
@@ -1241,7 +1242,10 @@ object Scanners {
       if migrateTo3 then canStartStatTokens2 else canStartStatTokens3
 
     def canStartExprTokens =
-      if migrateTo3 then canStartExprTokens2 else canStartExprTokens3
+      if migrateTo3 then 
+        canStartExprTokens2 
+      else 
+        canStartExprTokens3 | (if featureEnabled(Feature.unqualifiedSelectors) then BitSet(DOT) else BitSet.empty)
 
 // Literals -----------------------------------------------------------------
 

compiler/src/dotty/tools/dotc/parsing/Tokens.scala

@@ -227,7 +227,7 @@ object Tokens extends TokensCommon {
     | BitSet(QUOTE, NEW)
 
   final val canStartExprTokens3: TokenSet =
-    canStartInfixExprTokens | BitSet(INDENT, IF, WHILE, FOR, TRY, THROW, DOT)
+    canStartInfixExprTokens | BitSet(INDENT, IF, WHILE, FOR, TRY, THROW)
 
   final val canStartExprTokens2: TokenSet = canStartExprTokens3 | BitSet(DO)
 

library/src/scala/language.scala

@@ -355,6 +355,11 @@ object language {
     @compileTimeOnly("`subCases` can only be used at compile time in import statements")
     object subCases
 
+    /** Experimental support for unqualified selectors
+     */
+    @compileTimeOnly("`unqualifiedSelectors` can only be used at compile time in import statements")
+    object unqualifiedSelectors
+
   }
 
     /** The deprecated object contains features that are no longer officially suypported in Scala.

library/src/scala/runtime/stdLibPatches/language.scala

@@ -161,6 +161,11 @@ object language:
      */
     @compileTimeOnly("`subCases` can only be used at compile time in import statements")
     object subCases
+
+    /** Experimental support for unqualified selectors
+     */
+    @compileTimeOnly("`unqualifiedSelectors` can only be used at compile time in import statements")
+    object unqualifiedSelectors
   end experimental
 
   /** The deprecated object contains features that are no longer officially suypported in Scala.

tests/pos/unqualified-selector-enum.scala

@@ -1,3 +1,5 @@
+import scala.language.experimental.unqualifiedSelectors
+
 enum Opt[+T]:
   case none extends Opt[Nothing]
   case some[T](value: T) extends Opt[T]

tests/pos/unqualified-selector-object.scala

@@ -1,3 +1,5 @@
+import scala.language.experimental.unqualifiedSelectors
+
 class Opt[+T](v: T)
 
 object Opt: