Remove Inlined trees before erasure

In this first step we remove the Inlined trees in FirstTransform just after unpickling.
We also remove the YCheckPositions wich checked that all changes in sources where wrapped in Inline nodes.
This invariant does not hold after FirstTransform anymore.
YCheckPositions was added to make sure that the transformation fases kept the Inlined nodes until erasure which is not needed anymore.

Author: nicolasstucki

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -37,7 +37,6 @@ class Compiler {
   /** Phases dealing with the frontend up to trees ready for TASTY pickling */
   protected def frontendPhases: List[List[Phase]] =
     List(new FrontEnd) ::           // Compiler frontend: scanner, parser, namer, typer
-    List(new YCheckPositions) ::    // YCheck positions
     List(new sbt.ExtractDependencies) :: // Sends information on classes' dependencies to sbt via callbacks
     List(new semanticdb.ExtractSemanticDB) :: // Extract info into .semanticdb files
     List(new PostTyper) ::          // Additional checks and cleanups after type checking

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

@@ -847,17 +847,18 @@ object Erasure {
     override def typedTry(tree: untpd.Try, pt: Type)(using Context): Try =
       super.typedTry(tree, adaptProto(tree, pt))
 
+    override def typedBlock(tree: untpd.Block, pt: Type)(using Context): Tree =
+      super.typedBlock(tree, pt) match
+        // Drop empty block after it has been repositioned (see Inliner.reposition)
+        case Block(Nil, expr) => expr
+        case block => block
+
     private def adaptProto(tree: untpd.Tree, pt: Type)(using Context) =
       if (pt.isValueType) pt else
         if (tree.typeOpt.derivesFrom(ctx.definitions.UnitClass))
           tree.typeOpt
         else valueErasure(tree.typeOpt)
 
-    override def typedInlined(tree: untpd.Inlined, pt: Type)(using Context): Tree =
-      super.typedInlined(tree, pt) match {
-        case tree: Inlined => Inliner.dropInlined(tree)
-      }
-
     override def typedValDef(vdef: untpd.ValDef, sym: Symbol)(using Context): Tree =
       if (sym.isEffectivelyErased) erasedDef(sym)
       else

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

@@ -214,6 +214,9 @@ class FirstTransform extends MiniPhase with InfoTransformer { thisPhase =>
     case _ => tree
   }
 
+  override def transformInlined(tree: Inlined)(using Context): Tree =
+    cpy.Block(tree)(tree.bindings, tree.expansion)
+
   // invariants: all modules have companion objects
   // all types are TypeTrees
   // all this types are explicit

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

@@ -205,11 +205,6 @@ object Inliner {
         using ctx.withOwner(retainer)))
     .reporting(i"retainer for $meth: $result", inlining)
 
-  /** Replace `Inlined` node by a block that contains its bindings and expansion */
-  def dropInlined(inlined: Inlined)(using Context): Tree =
-    if inlined.bindings.isEmpty then inlined.expansion
-    else cpy.Block(inlined)(inlined.bindings, inlined.expansion)
-
   def reposition(tree: Tree, callSpan: Span)(using Context): Tree = {
     // Reference test tests/run/i4947b
 

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

@@ -134,7 +134,7 @@ class InlineBytecodeTests extends DottyBytecodeTest {
       val expected =
         List(
           Label(0),
-          LineNumber(6, Label(0)),
+          LineNumber(2, Label(0)), // TODO this lable seems to not be used
           LineNumber(3, Label(0)),
           VarOp(ALOAD, 0),
           Ldc(LDC, "tracking"),
@@ -199,7 +199,7 @@ class InlineBytecodeTests extends DottyBytecodeTest {
       val expected =
         List(
           Label(0),
-          LineNumber(12, Label(0)),
+          LineNumber(6, Label(0)), // TODO this lable seems to not be used
           LineNumber(7, Label(0)),
           VarOp(ALOAD, 0),
           Ldc(LDC, "tracking"),
@@ -259,7 +259,7 @@ class InlineBytecodeTests extends DottyBytecodeTest {
       val expected =
         List(
           Label(0),
-          LineNumber(12, Label(0)),
+          LineNumber(2, Label(0)), // TODO this lable seems to not be used
           LineNumber(3, Label(0)),
           VarOp(ALOAD, 0),
           Ldc(LDC, "tracking2"),
@@ -320,7 +320,7 @@ class InlineBytecodeTests extends DottyBytecodeTest {
       val expected =
         List(
           Label(0),
-          LineNumber(13, Label(0)),
+          LineNumber(2, Label(0)), // TODO this lable seems to not be used
           LineNumber(3, Label(0)),
           VarOp(ALOAD, 0),
           Ldc(LDC, "tracking2"),