Handle byname parameters

Author: odersky

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -79,14 +79,14 @@ class Compiler {
          new RefChecks,              // Various checks mostly related to abstract members and overriding
          new TryCatchPatterns,       // Compile cases in try/catch
          new PatternMatcher) ::      // Compile pattern matches
+    List(new PreRecheck) ::          // Preparations for check captures phase, enabled under -Ycc
+    List(new CheckCaptures) ::       // Check captures, enabled under -Ycc
     List(new ElimOpaque,             // Turn opaque into normal aliases
          new sjs.ExplicitJSClasses,  // Make all JS classes explicit (Scala.js only)
          new ExplicitOuter,          // Add accessors to outer classes from nested ones.
          new ExplicitSelf,           // Make references to non-trivial self types explicit as casts
          new ElimByName,             // Expand by-name parameter references
          new StringInterpolatorOpt) :: // Optimizes raw and s string interpolators by rewriting them to string concatenations
-    List(new PreRecheck) ::          // Preparations for check captures phase, enabled under -Ycc
-    List(new CheckCaptures) ::       // Check captures, enabled under -Ycc
     List(new PruneErasedDefs,        // Drop erased definitions from scopes and simplify erased expressions
          new UninitializedDefs,      // Replaces `compiletime.uninitialized` by `_`
          new InlinePatterns,         // Remove placeholders of inlined patterns

compiler/src/dotty/tools/dotc/transform/Recheck.scala

@@ -199,7 +199,7 @@ abstract class Recheck extends Phase, IdentityDenotTransformer:
       if !tree.rhs.isEmpty then recheck(tree.rhs, sym.info)
 
     def recheckDefDef(tree: DefDef, sym: Symbol)(using Context): Unit =
-      val rhsCtx = linkConstructorParams(sym)
+      val rhsCtx = linkConstructorParams(sym).withOwner(sym)
       if !tree.rhs.isEmpty && !sym.isInlineMethod && !sym.isEffectivelyErased then
         inContext(rhsCtx) { recheck(tree.rhs, recheck(tree.tpt)) }
 
@@ -354,7 +354,7 @@ abstract class Recheck extends Phase, IdentityDenotTransformer:
      *  @param tree        the original tree
      *  @param pt          the expected result type
      */
-    def recheck(tree: Tree, pt: Type = WildcardType)(using Context): Type = trace(i"rechecking $tree with pt = $pt", recheckr, show = true) {
+    def recheckStart(tree: Tree, pt: Type = WildcardType)(using Context): Type =
 
       def recheckNamed(tree: NameTree, pt: Type)(using Context): Type =
         val sym = tree.symbol
@@ -397,18 +397,23 @@ abstract class Recheck extends Phase, IdentityDenotTransformer:
         case tree: PackageDef => recheckPackageDef(tree)
         case tree: Thicket => defn.NothingType
 
-      try
-        val result = tree match
-          case tree: NameTree => recheckNamed(tree, pt)
-          case tree => recheckUnnamed(tree, pt)
-        checkConforms(result, pt, tree)
-        if keepTypes then result.rememberFor(tree)
-        result
-      catch case ex: Exception =>
-        println(i"error while rechecking $tree")
-        throw ex
-    }
-    end recheck
+      tree match
+        case tree: NameTree => recheckNamed(tree, pt)
+        case tree => recheckUnnamed(tree, pt)
+    end recheckStart
+
+    def recheckFinish(tpe: Type, tree: Tree, pt: Type)(using Context): Type =
+      checkConforms(tpe, pt, tree)
+      if keepTypes then tpe.rememberFor(tree)
+      tpe
+
+    def recheck(tree: Tree, pt: Type = WildcardType)(using Context): Type =
+      trace(i"rechecking $tree with pt = $pt", recheckr, show = true) {
+        try recheckFinish(recheckStart(tree, pt), tree, pt)
+        catch case ex: Exception =>
+          println(i"error while rechecking $tree")
+          throw ex
+      }
 
     private val debugSuccesses = false
 

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

@@ -364,9 +364,25 @@ class CheckCaptures extends Recheck:
           .showing(i"constr type $mt with $argTypes%, % in $cls = $result", capt)
       else ownType
 
+    def recheckByNameArg(tree: Tree, pt: Type)(using Context): Type =
+      val closureDef(mdef) = tree
+      val arg = mdef.rhs
+      val localSet = CaptureSet.Var()
+      curEnv = Env(mdef.symbol, localSet, isBoxed = false, curEnv)
+      val result =
+        try
+          inContext(ctx.withOwner(mdef.symbol)) {
+            recheckStart(arg, pt).capturing(localSet)
+          }
+        finally curEnv = curEnv.outer
+      recheckFinish(result, arg, pt)
+
     override def recheckApply(tree: Apply, pt: Type)(using Context): Type =
-      includeCallCaptures(tree.symbol, tree.srcPos)
-      super.recheckApply(tree, pt)
+      if tree.symbol == defn.cbnArg then
+        recheckByNameArg(tree.args(0), pt)
+      else
+        includeCallCaptures(tree.symbol, tree.srcPos)
+        super.recheckApply(tree, pt)
 
     override def recheck(tree: Tree, pt: Type = WildcardType)(using Context): Type =
       val res = super.recheck(tree, pt)

tests/neg-custom-args/captures/byname.scala

@@ -0,0 +1,10 @@
+class CC
+type Cap = {*} CC
+
+def test(cap1: Cap, cap2: Cap) =
+  def f() = if cap1 == cap1 then g else g
+  def g(x: Int) = if cap2 == cap2 then 1 else x
+  def h(ff: => {cap2} Int => Int) = ff
+  h(f())  // error
+
+

tests/pos-custom-args/captures/byname.scala

@@ -0,0 +1,10 @@
+class CC
+type Cap = {*} CC
+
+class I
+
+def test(cap1: Cap, cap2: Cap): {cap1} I =
+  def f() = if cap1 == cap1 then I() else I()
+  def h(x: => {cap1} I) = x
+  h(f())
+