Handle inlining of statements in inline trait body

Statements in the body of an inline trait need to be inlined properly:
- before any statement of the implementing child
- making sure that the body is not executed twice (statements removed in Inlining)

Author: timotheeandres

compiler/src/dotty/tools/dotc/inlines/Inlines.scala

@@ -220,7 +220,7 @@ object Inlines:
             val overriddenSymbols = clsOverriddenSyms ++ defs.flatMap(_.symbol.allOverriddenSymbols)
             defs ::: InlineParentTrait(parent)(using ctx.withOwner(cls.symbol)).expandDefs(overriddenSymbols)
         )
-        val impl1 = cpy.Template(impl)(body = impl.body ::: inlineDefs)
+        val impl1 = cpy.Template(impl)(body = inlineDefs ::: impl.body)
         cpy.TypeDef(cls)(rhs = impl1)
       case _ =>
         cls
@@ -531,8 +531,13 @@ object Inlines:
     def expandDefs(overriddenDecls: Set[Symbol]): List[Tree] =
       paramAccessorsMapper.registerParamValuesOf(parent)
       val stats = Inlines.defsToInline(parentSym).filterNot(stat => overriddenDecls.contains(stat.symbol))
-      val inlinedSymbols = stats.map(stat => inlinedSym(stat.symbol))
-      stats.zip(inlinedSymbols).map(expandStat)
+      stats.map{
+        case member: MemberDef => Left((member, inlinedSym(member.symbol)))
+        case stat => Right(stat)
+      }.map{
+        case Left((tree, inlinedSym)) => expandStat(tree, inlinedSym)
+        case Right(tree) => inlinedRhs(tree)
+      }
     end expandDefs
 
     protected class InlineTraitTypeMap extends InlinerTypeMap {

compiler/src/dotty/tools/dotc/transform/Inlining.scala

@@ -68,7 +68,7 @@ class Inlining extends MacroTransform, SymTransformer {
     else
       sym
 
-  def transformInnerClasses(inlineTrait: TypeDef)(using Context): TypeDef =
+  def transformInlineTrait(inlineTrait: TypeDef)(using Context): TypeDef =
     val tpd.TypeDef(_, tmpl: Template) = inlineTrait: @unchecked
     val body1 = tmpl.body.flatMap {
       case innerClass @ tpd.TypeDef(name, tmpl1: Template) =>
@@ -89,8 +89,10 @@ class Inlining extends MacroTransform, SymTransformer {
           nestingLevel = innerClass.symbol.nestingLevel,
         ).asType
         List(newTrait, TypeDef(newTypeSym))
-      case member =>
+      case member: MemberDef =>
         List(member)
+      case _ =>
+        Nil
     }
     val tmpl1 = cpy.Template(tmpl)(body = body1)
     cpy.TypeDef(inlineTrait)(rhs = tmpl1)
@@ -105,11 +107,11 @@ class Inlining extends MacroTransform, SymTransformer {
     override def transform(tree: Tree)(using Context): Tree = {
       tree match
         case tree: TypeDef if tree.symbol.isInlineTrait =>
-          transformInnerClasses(tree)
+          transformInlineTrait(tree)
         case tree: TypeDef if Inlines.needsInlining(tree) =>
           val tree1 = super.transform(tree).asInstanceOf[TypeDef]
           if tree1.tpe.isError then tree1
-          else if tree1.symbol.isInlineTrait then transformInnerClasses(tree1)
+          else if tree1.symbol.isInlineTrait then transformInlineTrait(tree1)
           else Inlines.inlineParentInlineTraits(tree1)
         case tree: MemberDef =>
           if tree.symbol.is(Inline) then tree

tests/run/inline-trait-body-statements.check

@@ -0,0 +1,8 @@
+1
+foo
+foo
+1
+foo
+bar
+bar
+bar

tests/run/inline-trait-body-statements.scala

@@ -0,0 +1,22 @@
+inline trait A[T]:
+  var x = 1
+  def foo =
+    if x == 1 then println("1")
+    x = 1 - x
+    println("foo")
+
+  foo
+  foo
+  foo
+
+class B extends A[Int]:
+  def bar =
+    if x == 1 then println("1")
+    println("bar")
+
+  bar
+  bar
+  bar
+
+@main def Test =
+  B()