Fix purity check for val inside of object (#19598)

Fixes #17317

Author: sjrd

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -578,8 +578,9 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
       sym.owner.isPrimitiveValueClass
       || sym.owner == defn.StringClass
       || defn.pureMethods.contains(sym)
+
     tree.tpe.isInstanceOf[ConstantType] && tree.symbol != NoSymbol && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
-    || fn.symbol.isStableMember && !fn.symbol.is(Lazy)  // constructors of no-inits classes are stable
+    || fn.symbol.isStableMember && fn.symbol.isConstructor // constructors of no-inits classes are stable
 
   /** The purity level of this reference.
    *  @return

tests/run/i17317-b.check

@@ -0,0 +1 @@
+hello world

tests/run/i17317-b.scala

@@ -0,0 +1,12 @@
+object foo {
+  object HelloGen {
+    println("hello world")
+  }
+  val Hello = HelloGen
+}
+
+import foo.Hello
+
+object Test {
+  def main(args: Array[String]): Unit = Hello: Unit
+}

tests/run/i17317.check

@@ -0,0 +1 @@
+hello world

tests/run/i17317.scala

@@ -0,0 +1,12 @@
+package object foo {
+  object HelloGen {
+    println("hello world")
+  }
+  val Hello = HelloGen
+}
+
+import foo.Hello
+
+object Test {
+  def main(args: Array[String]): Unit = Hello: Unit
+}