Copy @use and @consume annotations to parameter types

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

@@ -395,6 +395,9 @@ extension (tp: Type)
     RefinedType(tp, name,
       AnnotatedType(rinfo, Annotation(defn.RefineOverrideAnnot, util.Spans.NoSpan)))
 
+  def dropUseAndConsumeAnnots(using Context): Type =
+    tp.dropAnnot(defn.UseAnnot).dropAnnot(defn.ConsumeAnnot)
+
 extension (tp: MethodType)
   /** A method marks an existential scope unless it is the prefix of a curried method */
   def marksExistentialScope(using Context): Boolean =
@@ -490,18 +493,24 @@ extension (sym: Symbol)
   def hasTrackedParts(using Context): Boolean =
     !CaptureSet.ofTypeDeeply(sym.info).isAlwaysEmpty
 
-  /** `sym` is annotated @use or it is a type parameter with a matching
+  /** `sym` itself or its info is annotated @use or it is a type parameter with a matching
    *  @use-annotated term parameter that contains `sym` in its deep capture set.
    */
   def isUseParam(using Context): Boolean =
     sym.hasAnnotation(defn.UseAnnot)
+    || sym.info.hasAnnotation(defn.UseAnnot)
     || sym.is(TypeParam)
         && sym.owner.rawParamss.nestedExists: param =>
             param.is(TermParam) && param.hasAnnotation(defn.UseAnnot)
             && param.info.deepCaptureSet.elems.exists:
                 case c: TypeRef => c.symbol == sym
                 case _ => false
 
+  /** `sym` or its info is annotated with `@consume`. */
+  def isConsumeParam(using Context): Boolean =
+    sym.hasAnnotation(defn.ConsumeAnnot)
+    || sym.info.hasAnnotation(defn.ConsumeAnnot)
+
   def isUpdateMethod(using Context): Boolean =
     sym.isAllOf(Mutable | Method, butNot = Accessor)
 

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

@@ -716,7 +716,7 @@ class CheckCaptures extends Recheck, SymTransformer:
         funtpe.paramInfos.zipWithConserve(funtpe.paramNames): (formal, pname) =>
           val param = meth.paramNamed(pname)
           def copyAnnot(tp: Type, cls: ClassSymbol) = param.getAnnotation(cls) match
-            case Some(ann) => AnnotatedType(tp, ann)
+            case Some(ann) if !tp.hasAnnotation(cls) => AnnotatedType(tp, ann)
             case _ => tp
           copyAnnot(copyAnnot(formal, defn.UseAnnot), defn.ConsumeAnnot)
       funtpe.derivedLambdaType(paramInfos = paramInfosWithUses)
@@ -1616,7 +1616,10 @@ class CheckCaptures extends Recheck, SymTransformer:
       if noWiden(actual, expected) then
         actual
       else
-        val improvedVAR = improveCaptures(actual.widen.dealiasKeepAnnots, actual)
+        // Compute the widened type. Drop `@use` and `@consume` annotations from the type,
+        // since they obscures the capturing type.
+        val widened = actual.widen.dealiasKeepAnnots.dropUseAndConsumeAnnots
+        val improvedVAR = improveCaptures(widened, actual)
         val improved = improveReadOnly(improvedVAR, expected)
         val adapted = adaptBoxed(
             improved.withReachCaptures(actual), expected, tree,

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

@@ -620,7 +620,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
             if currentOwner.enclosingMethodOrClass.isProperlyContainedIn(refSym.maybeOwner.enclosingMethodOrClass) then
               report.error(em"""Separation failure: $descr non-local $refSym""", pos)
             else if refSym.is(TermParam)
-              && !refSym.hasAnnotation(defn.ConsumeAnnot)
+              && !refSym.isConsumeParam
               && currentOwner.isContainedIn(refSym.owner)
             then
               badParams += refSym
@@ -899,7 +899,7 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
     if !isUnsafeAssumeSeparate(tree) then trace(i"checking separate $tree"):
       checkUse(tree)
       tree match
-        case tree @ Select(qual, _) if tree.symbol.is(Method) && tree.symbol.hasAnnotation(defn.ConsumeAnnot) =>
+        case tree @ Select(qual, _) if tree.symbol.is(Method) && tree.symbol.isConsumeParam =>
           traverseChildren(tree)
           checkConsumedRefs(
               captures(qual).footprint(), qual.nuType,
@@ -962,4 +962,4 @@ class SepCheck(checker: CheckCaptures.CheckerAPI) extends tpd.TreeTraverser:
             consumeInLoopError(ref, pos)
         case _ =>
           traverseChildren(tree)
-end SepCheck
+end SepCheck

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -1117,7 +1117,7 @@ class Definitions {
 
   // Set of annotations that are not printed in types except under -Yprint-debug
   @tu lazy val SilentAnnots: Set[Symbol] =
-    Set(InlineParamAnnot, ErasedParamAnnot, RefineOverrideAnnot, SilentIntoAnnot)
+    Set(InlineParamAnnot, ErasedParamAnnot, RefineOverrideAnnot, SilentIntoAnnot, UseAnnot, ConsumeAnnot)
 
   // A list of annotations that are commonly used to indicate that a field/method argument or return
   // type is not null. These annotations are used by the nullification logic in JavaNullInterop to

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -4234,6 +4234,11 @@ object Types extends TypeUtils {
         paramType = addAnnotation(paramType, defn.InlineParamAnnot, param)
       if param.is(Erased) then
         paramType = addAnnotation(paramType, defn.ErasedParamAnnot, param)
+      // Copy `@use` and `@consume` annotations from parameter symbols to the type.
+      if param.hasAnnotation(defn.UseAnnot) then
+        paramType = addAnnotation(paramType, defn.UseAnnot, param)
+      if param.hasAnnotation(defn.ConsumeAnnot) then
+        paramType = addAnnotation(paramType, defn.ConsumeAnnot, param)
       paramType
 
     def adaptParamInfo(param: Symbol)(using Context): Type =

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -134,6 +134,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
 
   protected def argText(arg: Type, isErased: Boolean = false): Text =
     keywordText("erased ").provided(isErased)
+    ~ specialAnnotText(defn.UseAnnot, arg)
+    ~ specialAnnotText(defn.ConsumeAnnot, arg)
     ~ homogenizeArg(arg).match
         case arg: TypeBounds => "?" ~ toText(arg)
         case arg => toText(arg)
@@ -376,10 +378,18 @@ class PlainPrinter(_ctx: Context) extends Printer {
     try "(" ~ toTextRef(tp) ~ " : " ~ toTextGlobal(tp.underlying) ~ ")"
     finally elideCapabilityCaps = saved
 
+  /** Print the annotation that are meant to be on the parameter symbol but was moved
+   * to parameter types. Examples are `@use` and `@consume`. */
+  protected def specialAnnotText(sym: ClassSymbol, tp: Type): Text =
+    Str(s"@${sym.name} ").provided(tp.hasAnnotation(sym))
+
   protected def paramsText(lam: LambdaType): Text = {
     def paramText(ref: ParamRef) =
       val erased = ref.underlying.hasAnnotation(defn.ErasedParamAnnot)
-      keywordText("erased ").provided(erased) ~ ParamRefNameString(ref) ~ hashStr(lam) ~ toTextRHS(ref.underlying, isParameter = true)
+      keywordText("erased ").provided(erased)
+        ~ specialAnnotText(defn.UseAnnot, ref.underlying)
+        ~ specialAnnotText(defn.ConsumeAnnot, ref.underlying)
+        ~ ParamRefNameString(ref) ~ hashStr(lam) ~ toTextRHS(ref.underlying, isParameter = true)
     Text(lam.paramRefs.map(paramText), ", ")
   }
 

tests/neg-custom-args/captures/cc-annot-value-classes.scala

@@ -0,0 +1,18 @@
+import language.experimental.captureChecking
+import caps.*
+
+class Runner(val x: Int) extends AnyVal:
+  def runOps(@use ops: List[() => Unit]): Unit =
+    ops.foreach(_())  // ok
+
+class RunnerAlt(val x: Int):
+  def runOps(@use ops: List[() => Unit]): Unit =
+    ops.foreach(_())  // ok, of course
+
+class RunnerAltAlt(val x: Int) extends AnyVal:
+  def runOps(ops: List[() => Unit]): Unit =
+    ops.foreach(_())  // error, as expected
+
+class RunnerAltAltAlt(val x: Int):
+  def runOps(ops: List[() => Unit]): Unit =
+    ops.foreach(_())  // error, as expected

tests/neg-custom-args/captures/cc-annot-value-classes2.scala

@@ -0,0 +1,16 @@
+import language.experimental.captureChecking
+import caps.*
+trait Ref extends Mutable
+def kill(@consume x: Ref^): Unit = ()
+
+class C1:
+  def myKill(@consume x: Ref^): Unit = kill(x)  // ok
+
+class C2(val dummy: Int) extends AnyVal:
+  def myKill(@consume x: Ref^): Unit = kill(x)  // ok, too
+
+class C3:
+  def myKill(x: Ref^): Unit = kill(x)  // error
+
+class C4(val dummy: Int) extends AnyVal:
+  def myKill(x: Ref^): Unit = kill(x)  // error, too

tests/neg-custom-args/captures/leak-problem-unboxed.scala

@@ -19,14 +19,14 @@ def useBoxedAsync1(@use x: Box[Async^]): Unit = x.get.read() // ok
 def test(): Unit =
 
   val f: Box[Async^] => Unit = (x:  Box[Async^]) => useBoxedAsync(x) // error
-  val _: Box[Async^] => Unit = useBoxedAsync(_) // error
-  val _: Box[Async^] => Unit = useBoxedAsync // error
-  val _ = useBoxedAsync(_) // error
-  val _ = useBoxedAsync // error
+  val t1: Box[Async^] => Unit = useBoxedAsync(_) // error
+  val t2: Box[Async^] => Unit = useBoxedAsync // error
+  val t3 = useBoxedAsync(_) // was error, now ok
+  val t4 = useBoxedAsync // was error, now ok
 
   def boom(x: Async^): () ->{f} Unit =
     () => f(Box(x))
 
   val leaked = usingAsync[() ->{f} Unit](boom)
 
-  leaked()  // scope violation
+  leaked()  // scope violation

tests/neg-custom-args/captures/unbox-overrides.check

@@ -1,21 +1,21 @@
 -- [E164] Declaration Error: tests/neg-custom-args/captures/unbox-overrides.scala:8:6 ----------------------------------
 8 |  def foo(x: C): C        // error
   |      ^
-  |error overriding method foo in trait A of type (x: C): C;
+  |error overriding method foo in trait A of type (@use x: C): C;
   |  method foo of type (x: C): C has a parameter x with different @use status than the corresponding parameter in the overridden definition
   |
   | longer explanation available when compiling with `-explain`
 -- [E164] Declaration Error: tests/neg-custom-args/captures/unbox-overrides.scala:9:6 ----------------------------------
 9 |  def bar(@use x: C): C // error
   |      ^
   |error overriding method bar in trait A of type (x: C): C;
-  |  method bar of type (x: C): C has a parameter x with different @use status than the corresponding parameter in the overridden definition
+  |  method bar of type (@use x: C): C has a parameter x with different @use status than the corresponding parameter in the overridden definition
   |
   | longer explanation available when compiling with `-explain`
 -- [E164] Declaration Error: tests/neg-custom-args/captures/unbox-overrides.scala:15:15 --------------------------------
 15 |abstract class C extends A[C], B2 // error
    |               ^
-   |error overriding method foo in trait A of type (x: C): C;
+   |error overriding method foo in trait A of type (@use x: C): C;
    |  method foo in trait B2 of type (x: C): C has a parameter x with different @use status than the corresponding parameter in the overridden definition
    |
    | longer explanation available when compiling with `-explain`

tests/neg-custom-args/captures/unsound-reach-4.check

@@ -18,9 +18,9 @@
 17 |  def use(@consume x: F): File^ = x // error @consume override
    |      ^
    |      error overriding method use in trait Foo of type (x: File^): box File^;
-   |        method use of type (x: File^): File^² has incompatible type
+   |        method use of type (@consume x: File^): File^² has incompatible type
    |
    |      where:    ^  refers to the universal root capability
-   |                ^² refers to a root capability associated with the result type of (x: File^): File^²
+   |                ^² refers to a root capability associated with the result type of (@consume x: File^): File^²
    |
    | longer explanation available when compiling with `-explain`

tests/pos-custom-args/captures/cc-use-iterable.scala

@@ -0,0 +1,10 @@
+import language.experimental.captureChecking
+trait IterableOnce[+T]
+trait Iterable[+T] extends IterableOnce[T]:
+  def flatMap[U](@caps.use f: T => IterableOnce[U]^): Iterable[U]^{this, f*}
+
+
+class IterableOnceExtensionMethods[T](val it: IterableOnce[T]) extends AnyVal:
+  def flatMap[U](@caps.use f: T => IterableOnce[U]^): IterableOnce[U]^{f*} = it match
+    case it: Iterable[T] => it.flatMap(f)
+