Standardize how previously experimental features are handled (#21686)

If a feature was previously experimental and is now standard, we change
any tests for that feature to be only dependent on the source version
where the feature was standardized. Language imports in old source
versions will no longer enable the feature. (And these language imports
also come with a deprecation message).

If a feature was previously experimental and is now dropped, the feature
becomes unavailable also in old versions.

The motivation to do it this way is to insist that experimental features
are ephemeral. We should not be able to rely on an experimental feature
forever in an old version.

This commit implements this policy for fewerBraces and
clauseInterleaving. Two implemented extensions (relaxedExtensionImports,
betterMatchTypeExtractors) already implemented it before.

Author: hamzaremmal

community-build/community-projects/intent

@@ -28,9 +28,7 @@ object Feature:
   val dependent = experimental("dependent")
   val erasedDefinitions = experimental("erasedDefinitions")
   val symbolLiterals = deprecated("symbolLiterals")
-  val fewerBraces = experimental("fewerBraces")
   val saferExceptions = experimental("saferExceptions")
-  val clauseInterleaving = experimental("clauseInterleaving")
   val pureFunctions = experimental("pureFunctions")
   val captureChecking = experimental("captureChecking")
   val into = experimental("into")
@@ -60,9 +58,7 @@ object Feature:
     (dependent, "Allow dependent method types"),
     (erasedDefinitions, "Allow erased definitions"),
     (symbolLiterals, "Allow symbol literals"),
-    (fewerBraces, "Enable support for using indentation for arguments"),
     (saferExceptions, "Enable safer exceptions"),
-    (clauseInterleaving, "Enable clause interleaving"),
     (pureFunctions, "Enable pure functions for capture checking"),
     (captureChecking, "Enable experimental capture checking"),
     (into, "Allow into modifier on parameter types"),
@@ -124,9 +120,6 @@ object Feature:
 
   def namedTypeArgsEnabled(using Context) = enabled(namedTypeArguments)
 
-  def clauseInterleavingEnabled(using Context) =
-    sourceVersion.isAtLeast(`3.6`) || enabled(clauseInterleaving)
-
   def betterForsEnabled(using Context) = enabled(betterFors)
 
   def genericNumberLiteralsEnabled(using Context) = enabled(genericNumberLiterals)
@@ -169,9 +162,6 @@ object Feature:
   def migrateTo3(using Context): Boolean =
     sourceVersion == `3.0-migration`
 
-  def fewerBracesEnabled(using Context) =
-    sourceVersion.isAtLeast(`3.3`) || enabled(fewerBraces)
-
   /** If current source migrates to `version`, issue given warning message
    *  and return `true`, otherwise return `false`.
    */

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

@@ -31,6 +31,11 @@ enum SourceVersion:
 
   def isAtMost(v: SourceVersion) = stable.ordinal <= v.ordinal
 
+  def enablesFewerBraces = isAtLeast(`3.3`)
+  def enablesClauseInterleaving = isAtLeast(`3.6`)
+  def enablesNewGivens = isAtLeast(`3.6`)
+  def enablesNamedTuples = isAtLeast(`3.7`)
+
 object SourceVersion extends Property.Key[SourceVersion]:
   def defaultSourceVersion = `3.7`
 

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

@@ -885,7 +885,7 @@ object Parsers {
         }
       })
       canRewrite &= (in.isAfterLineEnd || statCtdTokens.contains(in.token)) // test (5)
-      if canRewrite && (!underColonSyntax || Feature.fewerBracesEnabled) then
+      if canRewrite && (!underColonSyntax || sourceVersion.enablesFewerBraces) then
         val openingPatchStr =
           if !colonRequired then ""
           else if testChar(startOpening - 1, Chars.isOperatorPart(_)) then " :"
@@ -1011,7 +1011,7 @@ object Parsers {
       skipParams()
       lookahead.isColon
       && {
-        !sourceVersion.isAtLeast(`3.6`)
+        !sourceVersion.enablesNewGivens
         || { // in the new given syntax, a `:` at EOL after an identifier represents a single identifier given
              // Example:
              //    given C:
@@ -1165,7 +1165,7 @@ object Parsers {
      *      body
      */
     def isColonLambda =
-      Feature.fewerBracesEnabled && in.token == COLONfollow && followingIsLambdaAfterColon()
+      sourceVersion.enablesFewerBraces && in.token == COLONfollow && followingIsLambdaAfterColon()
 
     /**   operand { infixop operand | MatchClause } [postfixop],
      *
@@ -1870,7 +1870,7 @@ object Parsers {
       infixOps(t, canStartInfixTypeTokens, operand, Location.ElseWhere, ParseKind.Type,
         isOperator = !followingIsVararg()
                      && !isPureArrow
-                     && !(isIdent(nme.as) && sourceVersion.isAtLeast(`3.6`) && inContextBound)
+                     && !(isIdent(nme.as) && sourceVersion.enablesNewGivens && inContextBound)
                      && nextCanFollowOperator(canStartInfixTypeTokens))
 
     /** RefinedType   ::=  WithType {[nl] Refinement} [`^` CaptureSet]
@@ -2263,7 +2263,7 @@ object Parsers {
     def contextBound(pname: TypeName): Tree =
       val t = toplevelTyp(inContextBound = true)
       val ownName =
-        if isIdent(nme.as) && sourceVersion.isAtLeast(`3.6`) then
+        if isIdent(nme.as) && sourceVersion.enablesNewGivens then
           in.nextToken()
           ident()
         else EmptyTermName
@@ -2276,7 +2276,7 @@ object Parsers {
     def contextBounds(pname: TypeName): List[Tree] =
       if in.isColon then
         in.nextToken()
-        if in.token == LBRACE && sourceVersion.isAtLeast(`3.6`)
+        if in.token == LBRACE && sourceVersion.enablesNewGivens
         then inBraces(commaSeparated(() => contextBound(pname)))
         else
           val bound = contextBound(pname)
@@ -3500,7 +3500,7 @@ object Parsers {
           val hkparams = typeParamClauseOpt(ParamOwner.Hk)
           val bounds =
             if paramOwner.acceptsCtxBounds then typeAndCtxBounds(name)
-            else if sourceVersion.isAtLeast(`3.6`) && paramOwner == ParamOwner.Type then typeAndCtxBounds(name)
+            else if sourceVersion.enablesNewGivens && paramOwner == ParamOwner.Type then typeAndCtxBounds(name)
             else typeBounds()
           TypeDef(name, lambdaAbstract(hkparams, bounds)).withMods(mods)
         }
@@ -3969,7 +3969,7 @@ object Parsers {
         val ident = termIdent()
         var name = ident.name.asTermName
         val paramss =
-          if Feature.clauseInterleavingEnabled(using in.languageImportContext) then
+          if sourceVersion.enablesClauseInterleaving then
             typeOrTermParamClauses(ParamOwner.Def, numLeadParams)
           else
             val tparams = typeParamClauseOpt(ParamOwner.Def)
@@ -4069,7 +4069,7 @@ object Parsers {
           case SEMI | NEWLINE | NEWLINES | COMMA | RBRACE | OUTDENT | EOF =>
             makeTypeDef(typeAndCtxBounds(tname))
           case _ if (staged & StageKind.QuotedPattern) != 0
-              || sourceVersion.isAtLeast(`3.6`) && in.isColon =>
+              || sourceVersion.enablesNewGivens && in.isColon =>
             makeTypeDef(typeAndCtxBounds(tname))
           case _ =>
             syntaxErrorOrIncomplete(ExpectedTypeBoundOrEquals(in.token))
@@ -4244,7 +4244,7 @@ object Parsers {
     def givenDef(start: Offset, mods: Modifiers, givenMod: Mod) = atSpan(start, nameStart) {
       var mods1 = addMod(mods, givenMod)
       val nameStart = in.offset
-      var newSyntaxAllowed = sourceVersion.isAtLeast(`3.6`)
+      var newSyntaxAllowed = sourceVersion.enablesNewGivens
       val hasEmbeddedColon = !in.isColon && followingIsGivenDefWithColon()
       val name = if isIdent && hasEmbeddedColon then ident() else EmptyTermName
 

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

@@ -17,7 +17,7 @@ import scala.collection.mutable
 import scala.collection.immutable.SortedMap
 import rewrites.Rewrites.patch
 import config.Feature
-import config.Feature.{migrateTo3, fewerBracesEnabled}
+import config.Feature.migrateTo3
 import config.SourceVersion.{`3.0`, `3.0-migration`}
 import config.MigrationVersion
 import reporting.{NoProfile, Profile, Message}
@@ -664,7 +664,7 @@ object Scanners {
         if token == COLONop && inTemplate then
           report.deprecationWarning(em"`:` after symbolic operator is deprecated; use backticks around operator instead", sourcePos(offset))
           true
-        else token == COLONfollow && (inTemplate || fewerBracesEnabled)
+        else token == COLONfollow && (inTemplate || sourceVersion.enablesFewerBraces)
       if enabled then
         peekAhead()
         val atEOL = isAfterLineEnd || token == EOF