Support lazy val members

Author: bracevac

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

@@ -736,6 +736,14 @@ class CheckCaptures extends Recheck, SymTransformer:
         checkUpdate(qualType, tree.srcPos):
           i"Cannot call update ${tree.symbol} of ${qualType.showRef}"
 
+      // If selecting a lazy val member, charge the qualifier since accessing
+      // the lazy val can trigger initialization that uses the qualifier's capabilities
+      if tree.symbol.is(Lazy) then
+        qualType match
+          case tr: (TermRef | ThisType) =>
+            markPathFree(tr, pt, tree)
+          case _ =>
+
       val origSelType = recheckSelection(tree, qualType, name, disambiguate)
       val selType = mapResultRoots(origSelType, tree.symbol)
       val selWiden = selType.widen

tests/neg-custom-args/captures/lazyvals4.scala

@@ -0,0 +1,29 @@
+import language.experimental.captureChecking
+import caps.*
+
+class Console extends SharedCapability:
+  def println(msg: String): Unit = Predef.println("CONSOLE: " + msg)
+
+class IO extends SharedCapability:
+  def readLine(): String = scala.io.StdIn.readLine()
+
+class Clazz(val console: Console^):
+  lazy val memberLazy: () -> String = {
+    console.println("Computing memberLazy")
+    () => "Member Lazy Value"
+  }
+
+trait Trait:
+  lazy val memberLazy: () -> String
+  def memberMethod(): String
+
+def client(t: Trait^, c: Clazz^): Unit =
+  val v0:  () -> () -> String        = () => t.memberLazy     // error
+  val v0_1:  () ->{t} () -> String   = () => t.memberLazy     // ok
+  val v1:  () -> String              = () => t.memberLazy()   // error
+  val v2: (() -> String)^{t}         = () => t.memberLazy()   // ok
+  val v3: (() -> String)^{c.console} = () => c.memberLazy()   // error (but should this be allowed?)
+  val v4:  () -> String              = () => t.memberMethod() // error
+  val v5: (() -> String)^{t}         = () => t.memberMethod() // ok
+
+  ()