Keep track of method parameter symbols

Store the parameter symbols of a method in a `paramss`
field of the method symbol.

Parameter symbols are kept up-to-date until erasure.

Author: odersky

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

@@ -94,6 +94,7 @@ class TreeTypeMap(
           val (tmap1, tparams1) = transformDefs(ddef.tparams)
           val (tmap2, vparamss1) = tmap1.transformVParamss(vparamss)
           val res = cpy.DefDef(ddef)(name, tparams1, vparamss1, tmap2.transform(tpt), tmap2.transform(ddef.rhs))
+          res.symbol.setParamssFromDefs(tparams1, vparamss1)
           res.symbol.transformAnnotations {
             case ann: BodyAnnotation => ann.derivedAnnotation(transform(ann.tree))
             case ann => ann

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

@@ -208,6 +208,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
   def DefDef(sym: TermSymbol, tparams: List[TypeSymbol], vparamss: List[List[TermSymbol]],
              resultType: Type, rhs: Tree)(implicit ctx: Context): DefDef =
+    sym.setParamss(tparams, vparamss)
     ta.assignType(
       untpd.DefDef(
         sym.name,
@@ -223,15 +224,27 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def DefDef(sym: TermSymbol, rhsFn: List[List[Tree]] => Tree)(implicit ctx: Context): DefDef =
     polyDefDef(sym, Function.const(rhsFn))
 
+  /** A DefDef with given method symbol `sym`.
+   *  @rhsFn  A function from type parameter types and term parameter references
+   *          to the method's right-hand side.
+   *  Parameter symbols are taken from the `paramss` field of `sym`, or
+   *  are freshly generated if `paramss` is empty.
+   */
   def polyDefDef(sym: TermSymbol, rhsFn: List[Type] => List[List[Tree]] => Tree)(implicit ctx: Context): DefDef = {
-    val (tparams, mtp) = sym.info match {
+
+    val (tparams, existingParamss, mtp) = sym.info match {
       case tp: PolyType =>
-        val tparams = ctx.newTypeParams(sym, tp.paramNames, EmptyFlags, tp.instantiateParamInfos(_))
-        (tparams, tp.instantiate(tparams map (_.typeRef)))
-      case tp => (Nil, tp)
+        val (tparams, existingParamss) = sym.paramss match
+          case tparams :: vparamss =>
+            assert(tparams.hasSameLengthAs(tp.paramNames) && tparams.head.isType)
+            (tparams.asInstanceOf[List[TypeSymbol]], vparamss)
+          case _ =>
+            (ctx.newTypeParams(sym, tp.paramNames, EmptyFlags, tp.instantiateParamInfos(_)), Nil)
+        (tparams, existingParamss, tp.instantiate(tparams map (_.typeRef)))
+      case tp => (Nil, sym.paramss, tp)
     }
 
-    def valueParamss(tp: Type): (List[List[TermSymbol]], Type) = tp match {
+    def valueParamss(tp: Type, existingParamss: List[List[Symbol]]): (List[List[TermSymbol]], Type) = tp match {
       case tp: MethodType =>
         val isParamDependent = tp.isParamDependent
         val previousParamRefs = if (isParamDependent) mutable.ListBuffer[TermRef]() else null
@@ -254,14 +267,23 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
             makeSym(origInfo)
         }
 
-        val params = tp.paramNames.lazyZip(tp.paramInfos).map(valueParam)
-        val (paramss, rtp) = valueParamss(tp.instantiate(params map (_.termRef)))
+        val (params, existingParamss1) =
+          if tp.paramInfos.isEmpty then (Nil, existingParamss)
+          else existingParamss match
+            case vparams :: existingParamss1 =>
+              assert(vparams.hasSameLengthAs(tp.paramNames) && vparams.head.isTerm)
+              (vparams.asInstanceOf[List[TermSymbol]], existingParamss1)
+            case _ =>
+              (tp.paramNames.lazyZip(tp.paramInfos).map(valueParam), Nil)
+        val (paramss, rtp) =
+          valueParamss(tp.instantiate(params map (_.termRef)), existingParamss1)
         (params :: paramss, rtp)
       case tp => (Nil, tp.widenExpr)
     }
-    val (vparamss, rtp) = valueParamss(mtp)
+    val (vparamss, rtp) = valueParamss(mtp, existingParamss)
     val targs = tparams map (_.typeRef)
     val argss = vparamss.nestedMap(vparam => Ident(vparam.termRef))
+    sym.setParamss(tparams, vparamss)
     DefDef(sym, tparams, vparamss, rtp, rhsFn(targs)(argss))
   }
 

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

@@ -11,7 +11,7 @@ import Scopes.Scope
 import dotty.tools.io.AbstractFile
 import Decorators.SymbolIteratorDecorator
 import ast._
-import ast.Trees.{LambdaTypeTree, TypeBoundsTree}
+import ast.Trees.{LambdaTypeTree, TypeBoundsTree, ValDef, TypeDef}
 import Trees.Literal
 import Variances.Variance
 import annotation.tailrec
@@ -150,6 +150,7 @@ object SymDenotations {
     private var myFlags: FlagSet = adaptFlags(initFlags)
     private var myPrivateWithin: Symbol = initPrivateWithin
     private var myAnnotations: List[Annotation] = Nil
+    private var myParamss: List[List[Symbol]] = Nil
 
     /** The owner of the symbol; overridden in NoDenotation */
     def owner: Symbol = maybeOwner
@@ -372,6 +373,20 @@ object SymDenotations {
       case Nil => Nil
     }
 
+    /** If this is a method, the parameter symbols, by section.
+     *  Both type and value parameters are included. Empty sections are skipped.
+     */
+    final def paramss: List[List[Symbol]] = myParamss
+    final def paramss_=(pss: List[List[Symbol]]): Unit =
+      myParamss = pss
+
+    final def setParamss(tparams: List[Symbol], vparamss: List[List[Symbol]])(using Context): Unit =
+      paramss = (if tparams.isEmpty then vparamss else tparams :: vparamss)
+        .filterConserve(!_.isEmpty)
+
+    final def setParamssFromDefs(tparams: List[TypeDef[?]], vparamss: List[List[ValDef[?]]])(using Context): Unit =
+      setParamss(tparams.map(_.symbol), vparamss.map(_.map(_.symbol)))
+
     /** The denotation is completed: info is not a lazy type and attributes have defined values */
     final def isCompleted: Boolean = !myInfo.isInstanceOf[LazyType]
 
@@ -1450,16 +1465,20 @@ object SymDenotations {
       initFlags: FlagSet = UndefinedFlags,
       info: Type = null,
       privateWithin: Symbol = null,
-      annotations: List[Annotation] = null)(implicit ctx: Context): SymDenotation = {
+      annotations: List[Annotation] = null,
+      paramss: List[List[Symbol]] = null)(
+        using ctx: Context): SymDenotation = {
       // simulate default parameters, while also passing implicit context ctx to the default values
       val initFlags1 = (if (initFlags != UndefinedFlags) initFlags else this.flags)
       val info1 = if (info != null) info else this.info
       if (ctx.isAfterTyper && changedClassParents(info, info1, completersMatter = false))
         assert(ctx.phase.changesParents, i"undeclared parent change at ${ctx.phase} for $this, was: $info, now: $info1")
       val privateWithin1 = if (privateWithin != null) privateWithin else this.privateWithin
       val annotations1 = if (annotations != null) annotations else this.annotations
+      val paramss1 = if paramss != null then paramss else this.paramss
       val d = ctx.SymDenotation(symbol, owner, name, initFlags1, info1, privateWithin1)
       d.annotations = annotations1
+      d.paramss = paramss1
       d.registeredCompanion = registeredCompanion
       d
     }

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

@@ -97,8 +97,10 @@ class CompleteJavaEnums extends MiniPhase with InfoTransformer { thisPhase =>
   override def transformDefDef(tree: DefDef)(implicit ctx: Context): DefDef = {
     val sym = tree.symbol
     if (sym.isConstructor && sym.owner.derivesFromJavaEnum)
-      cpy.DefDef(tree)(
+      val tree1 = cpy.DefDef(tree)(
         vparamss = tree.vparamss.init :+ (tree.vparamss.last ++ addedParams(sym, Param)))
+      sym.setParamssFromDefs(tree1.tparams, tree1.vparamss)
+      tree1
     else if (sym.name == nme.DOLLAR_NEW && sym.owner.linkedClass.derivesFromJavaEnum) {
       val Block((tdef @ TypeDef(tpnme.ANON_CLASS, templ: Template)) :: Nil, call) = tree.rhs
       val args = tree.vparamss.last.takeRight(2).map(param => ref(param.symbol)).reverse

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

@@ -422,6 +422,14 @@ class TreeChecker extends Phase with SymTransformer {
     }
 
     override def typedDefDef(ddef: untpd.DefDef, sym: Symbol)(implicit ctx: Context): Tree =
+      def defParamss =
+        (ddef.tparams :: ddef.vparamss).filter(!_.isEmpty).map(_.map(_.symbol))
+      def layout(symss: List[List[Symbol]]): String =
+        symss.map(syms => i"($syms%, %)").mkString
+      assert(ctx.erasedTypes || sym.paramss == defParamss,
+        i"""param mismatch for ${sym.showLocated}:
+           |defined in tree  = ${layout(defParamss)}
+           |stored in symbol = ${layout(sym.paramss)}""")
       withDefinedSyms(ddef.tparams) {
         withDefinedSyms(ddef.vparamss.flatten) {
           if (!sym.isClassConstructor && !(sym.name eq nme.STATIC_CONSTRUCTOR))

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

@@ -1553,6 +1553,7 @@ class Namer { typer: Typer =>
     vparamss foreach completeParams
     def typeParams = tparams map symbolOfTree
     val termParamss = ctx.normalizeIfConstructor(vparamss.nestedMap(symbolOfTree), isConstructor)
+    sym.setParamss(typeParams, termParamss)
     def wrapMethType(restpe: Type): Type = {
       instantiateDependent(restpe, typeParams, termParamss)
       ctx.methodType(tparams map symbolOfTree, termParamss, restpe, isJava = ddef.mods.is(JavaDefined))