Make magic imply capyure checking

Comes with two bug fixes:

 (1) Maybe arguments should not be boxed.
 (2) Capture sets of module vals need to be interpolated

Author: odersky

compiler/src/dotty/tools/dotc/cc/CheckCaptures.scala

@@ -408,7 +408,7 @@ class CheckCaptures extends Recheck, SymTransformer:
      *  has been rechecked.
      */
     private def interpolateIfInferred(tpt: Tree, sym: Symbol)(using Context): Unit =
-      if tpt.isInstanceOf[InferredTypeTree] then
+      if tpt.isInstanceOf[InferredTypeTree] || sym.is(ModuleVal) then
         interpolate(tpt.nuType, sym)
           .showing(i"solved vars for $sym in ${tpt.nuType}", capt)
         anchorCaps(sym).traverse(tpt.nuType)

compiler/src/dotty/tools/dotc/cc/Setup.scala

@@ -311,9 +311,11 @@ class Setup extends PreRecheck, SymTransformer, SetupAPI:
         CapturingType(OrType(parent1, tp2, tp.isSoft), refs1, tp1.isBoxed)
       case tp @ OrType(tp1, tp2 @ CapturingType(parent2, refs2)) =>
         CapturingType(OrType(tp1, parent2, tp.isSoft), refs2, tp2.isBoxed)
-      case tp @ AppliedType(tycon, args)
-      if !defn.isFunctionClass(tp.dealias.typeSymbol) && (tp.dealias eq tp) =>
-        tp.derivedAppliedType(tycon, args.mapConserve(_.boxDeeply))
+      case tp @ AppliedType(tycon, args) if tp.dealias eq tp =>
+        val sym = tycon.typeSymbol
+        if !defn.isFunctionClass(sym) && sym != defn.MagicMaybeClass
+        then tp.derivedAppliedType(tycon, args.mapConserve(_.boxDeeply))
+        else tp
       case tp: RealTypeBounds =>
         tp.derivedTypeBounds(tp.lo, tp.hi.boxDeeply)
       case tp: LazyRef =>

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

@@ -327,26 +327,27 @@ object Feature:
    *  @return true iff the import was handled
    */
   def handleGlobalLanguageImport(prefix: TermName, imported: Name)(using Context): Boolean =
+    def enableCC() =
+      ctx.compilationUnit.needsCaptureChecking = true
+      if ctx.run != null then ctx.run.nn.ccEnabledSomewhere = true
     QualifiedName(prefix, imported.asTermName) match
       case `pureFunctions` =>
         ctx.compilationUnit.knowsPureFuns = true
         if ctx.run != null then ctx.run.nn.pureFunsImportEncountered = true
         true
       case `captureChecking` =>
-        ctx.compilationUnit.needsCaptureChecking = true
-        if ctx.run != null then ctx.run.nn.ccEnabledSomewhere = true
+        enableCC()
         true
       case `separationChecking` =>
-        ctx.compilationUnit.needsCaptureChecking = true
+        enableCC()
         ctx.compilationUnit.needsSeparationChecking = true
-        if ctx.run != null then ctx.run.nn.ccEnabledSomewhere = true
         true
       case `safe` =>
-        ctx.compilationUnit.needsCaptureChecking = true
+        enableCC()
         ctx.compilationUnit.safeMode = true
-        if ctx.run != null then ctx.run.nn.ccEnabledSomewhere = true
         true
       case `magic` =>
+        enableCC()
         ctx.compilationUnit.magic = true
         ctx.compilationUnit.sourceVersion = Some(SourceVersion.future)
         true

library/src/scala/Tuple.scala

@@ -6,7 +6,7 @@ import compiletime.*
 import compiletime.ops.int.*
 
 /** Tuple of arbitrary arity. */
-sealed trait Tuple extends Product {
+sealed trait Tuple extends Product, caps.Pure {
   import Tuple.*
 
   /** Creates a copy of this tuple as an Array. */

tests/neg-custom-args/captures/local-mutables-2.check

@@ -1,7 +1,7 @@
 -- Error: tests/neg-custom-args/captures/local-mutables-2.scala:7:9 ----------------------------------------------------
 7 |def foo() = // error: separation failure
   |         ^
-  |Separation failure in method foo's inferred result type (() ->{any.rd} Int, (x: Int) => Unit)^{}.
+  |Separation failure in method foo's inferred result type (() ->{any.rd} Int, (x: Int) => Unit).
   |One part,  () ->{any.rd} Int, hides capabilities  {any².rd}.
   |Another part,  (x: Int) => Unit,  captures capabilities  {any³, any, any²}.
   |The two sets overlap at  {`any` of value r}.
@@ -12,7 +12,7 @@
 -- Error: tests/neg-custom-args/captures/local-mutables-2.scala:11:10 --------------------------------------------------
 11 |def foo2() = // error: separation failure
    |          ^
-   |          Separation failure in method foo2's inferred result type (() ->{any.rd} Int, (x: Int) => Unit)^{}.
+   |          Separation failure in method foo2's inferred result type (() ->{any.rd} Int, (x: Int) => Unit).
    |          One part,  (x: Int) => Unit, hides capabilities  {any}.
    |          Another part,  () ->{any.rd} Int,  captures capabilities  {any.rd}.
    |          The two sets overlap at  {`any` of variable r}.

tests/run/fully-abstract-nat-maybe.scala

@@ -1,4 +1,5 @@
 //> using options -Yexplicit-nulls
+package test
 import language.experimental.magic
 import scala.magic.*
 import scala.reflect.ClassTag
@@ -74,7 +75,7 @@ object Test {
 
 }
 
-abstract class Numbers {
+abstract class Numbers extends caps.Pure {
 
   // === Nat ==========================================
   // Represents:
@@ -212,7 +213,7 @@ object IntImplementation extends Numbers {
     def pred: Nat = succ - 1
   }
 
-  private def intClassTag(cond: Int => Boolean): ClassTag[Int] = new ClassTag[Int] {
+  private def intClassTag(cond: Int -> Boolean): ClassTag[Int] = new ClassTag[Int] {
     def runtimeClass: Class[?] = classOf[Int]
     override def unapply(x: Any): Option[Int] = x match {
       case i: Int if cond(i) => Some(i)

tests/run/i13968-maybe.scala

@@ -5,15 +5,14 @@ object Bar {
 }
 
 object Bar23 {
-  def unapply(x: Any): Option[
+  def unapply(x: Any): (
       Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *:
       Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *: Int *:
       Int *: Int *: Int *: EmptyTuple
-  ] = Some(
+  )? = (
      1 *:  2 *:  3 *:  4 *:  5 *:  6 *:  7 *:  8 *:  9 *: 10 *:
     11 *: 12 *: 13 *: 14 *: 15 *: 16 *: 17 *: 18 *: 19 *: 20 *:
-    21 *: 22 *: 23 *: Tuple()
-  )
+    21 *: 22 *: 23 *: Tuple())
 }
 
 @main def Test() =