Backport "Disallow context function types as value-class parameters" to 3.3 LTS

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

@@ -192,9 +192,10 @@ private sealed trait WarningSettings:
       ChoiceWithHelp("linted", "Enable -Wunused:imports,privates,locals,implicits"),
       ChoiceWithHelp(
         name = "strict-no-implicit-warn",
-        description = "Same as -Wunused:import, only for imports of explicit named members.\n" +
-        "NOTE : This overrides -Wunused:imports and NOT set by -Wunused:all"
+        description = """Same as -Wunused:imports, only for imports of explicit named members.
+                        |NOTE : This overrides -Wunused:imports and NOT set by -Wunused:all""".stripMargin
       ),
+      ChoiceWithHelp("unsafe-warn-patvars", "Deprecated alias for `patvars`"),
     ),
     default = Nil
   )
@@ -219,7 +220,7 @@ private sealed trait WarningSettings:
     def params(using Context) = allOr("params")
     def privates(using Context) =
       allOr("privates") || allOr("linted")
-    def patvars(using Context) = allOr("patvars")
+    def patvars(using Context) = allOr("patvars") || isChoiceSet("unsafe-warn-patvars")
     def inlined(using Context) = isChoiceSet("inlined")
     def linted(using Context) =
       allOr("linted")

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

@@ -1677,9 +1677,8 @@ object Parsers {
         val start = in.offset
         val tparams = typeParamClause(ParamOwner.TypeParam)
         if in.token == TLARROW then
-          // Filter illegal context bounds and report syntax error
           atSpan(start, in.skipToken()):
-            LambdaTypeTree(tparams.mapConserve(stripContextBounds("type lambdas")), toplevelTyp())
+            LambdaTypeTree(tparams, toplevelTyp())
         else if in.token == ARROW || isPureArrow(nme.PUREARROW) then
           val arrowOffset = in.skipToken()
           val body = toplevelTyp()
@@ -1700,13 +1699,6 @@ object Parsers {
         typeRest(infixType())
     end typ
 
-    /** Removes context bounds from TypeDefs and returns a syntax error. */
-    private def stripContextBounds(in: String)(tparam: TypeDef) = tparam match
-      case TypeDef(name, rhs: ContextBounds) =>
-        syntaxError(em"context bounds are not allowed in $in", rhs.span)
-        TypeDef(name, rhs.bounds)
-      case other => other
-
     private def makeKindProjectorTypeDef(name: TypeName): TypeDef = {
       val isVarianceAnnotated = name.startsWith("+") || name.startsWith("-")
       // We remove the variance marker from the name without passing along the specified variance at all
@@ -3275,8 +3267,7 @@ object Parsers {
      *  TypTypeParam      ::=  {Annotation} id [HkTypePamClause] TypeBounds
      *
      *  HkTypeParamClause ::=  ‘[’ HkTypeParam {‘,’ HkTypeParam} ‘]’
-     *  HkTypeParam       ::=  {Annotation} [‘+’ | ‘-’]
-     *                         (id | ‘_’) [HkTypeParamClause] TypeBounds
+     *  HkTypeParam       ::=  {Annotation} [‘+’ | ‘-’] (id [HkTypePamClause] | ‘_’) TypeBounds
      */
     def typeParamClause(paramOwner: ParamOwner): List[TypeDef] = inBracketsWithCommas {
 

compiler/src/dotty/tools/dotc/typer/Checking.scala

@@ -755,6 +755,8 @@ object Checking {
         }
         clParamAccessors match {
           case param :: params =>
+            if (defn.isContextFunctionType(param.info))
+              report.error("value classes are not allowed for context function types", param.srcPos)
             if (param.is(Mutable))
               report.error(ValueClassParameterMayNotBeAVar(clazz, param), param.srcPos)
             if (param.info.isInstanceOf[ExprType])

tests/neg/i22552.check

@@ -2,7 +2,11 @@
 3 |  type A[X: TC]                     // error
   |          ^
   |          ']' expected, but ':' found
--- Error: tests/neg/i22552.scala:4:15 ----------------------------------------------------------------------------------
+-- [E040] Syntax Error: tests/neg/i22552.scala:4:13 --------------------------------------------------------------------
 4 |  type C = [X: TC] =>> List[X]      // error
-  |               ^^
-  |               context bounds are not allowed in type lambdas
+  |             ^
+  |             ']' expected, but ':' found
+-- [E040] Syntax Error: tests/neg/i22552.scala:5:13 --------------------------------------------------------------------
+5 |  type D = [X: TC] => () => List[X] // error
+  |             ^
+  |             ']' expected, but ':' found

tests/neg/i22552.scala

@@ -2,4 +2,4 @@ trait Foo:
   type TC[T]
   type A[X: TC]                     // error
   type C = [X: TC] =>> List[X]      // error
-  type D = [X: TC] => () => List[X] // allowed context bound
+  type D = [X: TC] => () => List[X] // error

tests/neg/i22752.scala

@@ -0,0 +1,4 @@
+class Inner(body: Int ?=> Int) extends AnyVal: // error
+  def rescue: Int ?=> Int = ???
+
+class Inner2(body: Int => Int) extends AnyVal // ok