Don't force info to get signature in TreeChecker

When we are reading a new definition from tasty and setting `info` of
a symbol in `readNewDef`:

          sym.info = methodType(paramss, resType)

The line above will reach `TreeChecker.transformSym`:

          assert(symd.signature == initial.signature

At the time, the `symd` is not yet completed. Getting signature of the
denotation will force the symbol and trigger completion of the info,
which reaches the `PositionTree` in `readIndexedDef.

compiler/src/dotty/tools/dotc/core/NamerOps.scala

@@ -11,15 +11,14 @@ import ast.untpd
 /** Operations that are shared between Namer and TreeUnpickler */
 object NamerOps:
 
-  /** The given type, unless `sym` is a constructor, in which case the
-   *  type of the constructed instance is returned
+  /** The type of the constructed instance is returned
+   *
+   *  @param ctor the constructor
    */
-  def effectiveResultType(sym: Symbol, paramss: List[List[Symbol]], givenTp: Type)(using Context): Type =
-    if sym.name == nme.CONSTRUCTOR then
-      paramss match
-        case TypeSymbols(tparams) :: _ => sym.owner.typeRef.appliedTo(tparams.map(_.typeRef))
-        case _ => sym.owner.typeRef
-    else givenTp
+  def effectiveResultType(ctor: Symbol, paramss: List[List[Symbol]])(using Context): Type =
+    paramss match
+      case TypeSymbols(tparams) :: _ => ctor.owner.typeRef.appliedTo(tparams.map(_.typeRef))
+      case _ => ctor.owner.typeRef
 
   /** if isConstructor, make sure it has one leading non-implicit parameter list */
   def normalizeIfConstructor(paramss: List[List[Symbol]], isConstructor: Boolean)(using Context): List[List[Symbol]] =

compiler/src/dotty/tools/dotc/core/tasty/TreePickler.scala

@@ -332,6 +332,7 @@ class TreePickler(pickler: TastyPickler) {
 
   def pickleDef(tag: Int, mdef: MemberDef, tpt: Tree, rhs: Tree = EmptyTree, pickleParams: => Unit = ())(using Context): Unit = {
     val sym = mdef.symbol
+
     assert(symRefs(sym) == NoAddr, sym)
     registerDef(sym)
     writeByte(tag)

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -831,7 +831,11 @@ class TreeUnpickler(reader: TastyReader,
           val tpt = readTpt()(using localCtx)
           val paramss = normalizeIfConstructor(
               paramDefss.nestedMap(_.symbol), name == nme.CONSTRUCTOR)
-          val resType = effectiveResultType(sym, paramss, tpt.tpe)
+          val resType =
+            if name == nme.CONSTRUCTOR then
+              effectiveResultType(sym, paramss)
+            else
+              tpt.tpe
           sym.info = methodType(paramss, resType)
           DefDef(paramDefss, tpt)
         case VALDEF =>

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

@@ -91,7 +91,7 @@ class TreeChecker extends Phase with SymTransformer {
     // until erasure, see the comment above `Compiler#phases`.
     if (ctx.phaseId <= erasurePhase.id) {
       val initial = symd.initial
-      assert(symd.signature == initial.signature,
+      assert(symd == initial || symd.signature == initial.signature,
         i"""Signature of ${sym.showLocated} changed at phase ${ctx.base.fusedContaining(ctx.phase.prev)}
            |Initial info: ${initial.info}
            |Initial sig : ${initial.signature}

compiler/src/dotty/tools/dotc/transform/init/Semantic.scala

@@ -795,6 +795,7 @@ class Semantic {
 
       // follow constructor
       if cls.hasSource then
+        printer.println("init super class " + cls.show)
         val res2 = thisV.call(ctor, superType = NoType, source)(using heap, ctx, trace.add(source))
         errorBuffer ++= res2.errors
 

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

@@ -1680,7 +1680,7 @@ class Namer { typer: Typer =>
     if (isConstructor) {
       // set result type tree to unit, but take the current class as result type of the symbol
       typedAheadType(ddef.tpt, defn.UnitType)
-      wrapMethType(effectiveResultType(sym, paramSymss, NoType))
+      wrapMethType(effectiveResultType(sym, paramSymss))
     }
     else valOrDefDefSig(ddef, sym, paramSymss, wrapMethType)
   }