Introduce untpd.syntheticUnitLiteral to allow detection of explicit unit provided by user from synthetic unit introduced by compiler

[Cherry-picked 8c52866][modified]

Author: WojciechMazur

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

@@ -190,7 +190,7 @@ object desugar {
     if isSetterNeeded(vdef) then
       val setterParam = makeSyntheticParameter(tpt = SetterParamTree().watching(vdef))
       // The rhs gets filled in later, when field is generated and getter has parameters (see Memoize miniphase)
-      val setterRhs = if (vdef.rhs.isEmpty) EmptyTree else unitLiteral
+      val setterRhs = if (vdef.rhs.isEmpty) EmptyTree else syntheticUnitLiteral
       val setter = cpy.DefDef(vdef)(
           name    = valName.setterName,
           paramss = (setterParam :: Nil) :: Nil,
@@ -1311,7 +1311,7 @@ object desugar {
   def block(tree: Block)(using Context): Block = tree.expr match {
     case EmptyTree =>
       cpy.Block(tree)(tree.stats,
-        unitLiteral.withSpan(if (tree.stats.isEmpty) tree.span else tree.span.endPos))
+        syntheticUnitLiteral.withSpan(if (tree.stats.isEmpty) tree.span else tree.span.endPos))
     case _ =>
       tree
   }
@@ -1811,7 +1811,7 @@ object desugar {
           case ts: Thicket => ts.trees.tail
           case t => Nil
         } map {
-          case Block(Nil, EmptyTree) => unitLiteral // for s"... ${} ..."
+          case Block(Nil, EmptyTree) => syntheticUnitLiteral // for s"... ${} ..."
           case Block(Nil, expr) => expr // important for interpolated string as patterns, see i1773.scala
           case t => t
         }
@@ -1839,7 +1839,7 @@ object desugar {
         val pats1 = if (tpt.isEmpty) pats else pats map (Typed(_, tpt))
         flatTree(pats1 map (makePatDef(tree, mods, _, rhs)))
       case ext: ExtMethods =>
-        Block(List(ext), unitLiteral.withSpan(ext.span))
+        Block(List(ext), syntheticUnitLiteral.withSpan(ext.span))
       case f: FunctionWithMods if f.hasErasedParams => makeFunctionWithValDefs(f, pt)
     }
     desugared.withSpan(tree.span)

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

@@ -481,7 +481,11 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   def InferredTypeTree(tpe: Type)(using Context): TypedSplice =
     TypedSplice(new InferredTypeTree().withTypeUnchecked(tpe))
 
-  def unitLiteral(implicit src: SourceFile): Literal = Literal(Constant(())).withAttachment(SyntheticUnit, ())
+  def unitLiteral(implicit src: SourceFile): Literal =
+    Literal(Constant(()))
+
+  def syntheticUnitLiteral(implicit src: SourceFile): Literal =
+    unitLiteral.withAttachment(SyntheticUnit, ())
 
   def ref(tp: NamedType)(using Context): Tree =
     TypedSplice(tpd.ref(tp))

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2284,7 +2284,7 @@ object Parsers {
               in.nextToken();
               val expr = subExpr()
               if expr.span.exists then expr
-              else unitLiteral // finally without an expression
+              else syntheticUnitLiteral // finally without an expression
             }
             else {
               if handler.isEmpty then
@@ -3768,10 +3768,10 @@ object Parsers {
             val stats = selfInvocation() :: (
               if (isStatSep) { in.nextToken(); blockStatSeq() }
               else Nil)
-            Block(stats, unitLiteral)
+            Block(stats, syntheticUnitLiteral)
           }
         }
-      else Block(selfInvocation() :: Nil, unitLiteral)
+      else Block(selfInvocation() :: Nil, syntheticUnitLiteral)
 
     /** SelfInvocation  ::= this ArgumentExprs {ArgumentExprs}
      */

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

@@ -2009,7 +2009,7 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
                             // because we do not know the internal type params and method params.
                             // Hence no adaptation is possible, and we assume WildcardType as prototype.
         (from, proto)
-    val expr1 = typedExpr(tree.expr orElse untpd.unitLiteral.withSpan(tree.span), proto)
+    val expr1 = typedExpr(tree.expr orElse untpd.syntheticUnitLiteral.withSpan(tree.span), proto)
     assignType(cpy.Return(tree)(expr1, from))
   end typedReturn
 

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

@@ -158,7 +158,7 @@ class ReplCompiler extends Compiler:
       def wrap(trees: List[untpd.Tree]): untpd.PackageDef = {
         import untpd.*
 
-        val valdef = ValDef("expr".toTermName, TypeTree(), Block(trees, unitLiteral).withSpan(Span(0, expr.length)))
+        val valdef = ValDef("expr".toTermName, TypeTree(), Block(trees, syntheticUnitLiteral).withSpan(Span(0, expr.length)))
         val tmpl = Template(emptyConstructor, Nil, Nil, EmptyValDef, List(valdef))
         val wrapper = TypeDef("$wrapper".toTypeName, tmpl)
           .withMods(Modifiers(Final))