Merge pull request #5703 from dotty-staging/fix-#5350

 Fix #5350: Fix purity of local lazy vals

Author: Blaisorblade

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

@@ -400,10 +400,12 @@ trait TypedTreeInfo extends TreeInfo[Type] { self: Trees.Instance[Type] =>
       def isKnownPureOp(sym: Symbol) =
         sym.owner.isPrimitiveValueClass || sym.owner == defn.StringClass
       if (tree.tpe.isInstanceOf[ConstantType] && isKnownPureOp(tree.symbol) // A constant expression with pure arguments is pure.
-          || fn.symbol.isStable
+          || (fn.symbol.isStable && !fn.symbol.is(Lazy))
           || fn.symbol.isPrimaryConstructor && fn.symbol.owner.isNoInitsClass) // TODO: include in isStable?
         minOf(exprPurity(fn), args.map(exprPurity)) `min` Pure
       else if (fn.symbol.is(Erased)) Pure
+      else if (fn.symbol.isStable /* && fn.symbol.is(Lazy) */)
+        minOf(exprPurity(fn), args.map(exprPurity)) `min` Idempotent
       else Impure
     case Typed(expr, _) =>
       exprPurity(expr)

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

@@ -29,6 +29,7 @@ class ReplPrinter(_ctx: Context) extends DecompilerPrinter(_ctx) {
     else Str(const.value.toString)
 
   override def dclText(sym: Symbol): Text = {
+    ("lazy": Text).provided(sym.is(Lazy)) ~~
     toText(sym) ~ {
       if (sym.is(Method)) toText(sym.info)
       else if (sym.isType && sym.info.isTypeAlias) toText(sym.info)

compiler/src/dotty/tools/repl/Rendering.scala

@@ -76,11 +76,8 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None) {
     val dcl = d.symbol.showUser
 
     try {
-      val resultValue =
-        if (d.symbol.is(Flags.Lazy)) Some("<lazy>")
-        else valueOf(d.symbol)
-
-      resultValue.map(value => s"$dcl = $value")
+      if (d.symbol.is(Flags.Lazy)) Some(dcl)
+      else valueOf(d.symbol).map(value => s"$dcl = $value")
     }
     catch { case ex: InvocationTargetException => Some(renderError(ex)) }
   }

compiler/test-resources/repl/i5350

@@ -0,0 +1,7 @@
+scala> def foo = { lazy val bar: Unit = { println("Hello") }; bar }
+def foo: Unit
+scala> foo
+Hello
+scala> { lazy val bar: Unit = { println("Hello") }; bar }
+Hello
+lazy val bar: Unit

tests/run/i5350.check

@@ -0,0 +1 @@
+Hello

tests/run/i5350.scala

@@ -0,0 +1,10 @@
+object Test {
+  def foo = {
+    lazy val bar: Unit = println("Hello")
+    bar
+  }
+
+  def main(args: Array[String]): Unit = {
+    foo
+  }
+}

tests/run/i5350b.check

@@ -0,0 +1 @@
+Hello

tests/run/i5350b.scala

@@ -0,0 +1,10 @@
+object Test {
+  def foo: Unit = {
+    object bar { println("Hello") }
+    bar
+  }
+
+  def main(args: Array[String]): Unit = {
+    foo
+  }
+}

tests/run/i5350c.check

@@ -0,0 +1 @@
+Hello

tests/run/i5350c.scala

@@ -0,0 +1,10 @@
+object Test {
+  def foo: Unit = {
+    bar
+  }
+
+  def main(args: Array[String]): Unit = {
+    foo
+  }
+}
+object bar { println("Hello") }