Fix GADT-related memory leak

There was a confusion which led to the wrong gadt map being used
for pattern-bound variables if there was no other GADT variable
in the enclosing method.

This led to the outermost gadt map in the initial context being
populated with type bounds which never went away.

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

@@ -476,6 +476,7 @@ object Contexts {
     def setRunInfo(runInfo: RunInfo): this.type = { this.runInfo = runInfo; this }
     def setDiagnostics(diagnostics: Option[StringBuilder]): this.type = { this.diagnostics = diagnostics; this }
     def setGadt(gadt: GADTMap): this.type = { this.gadt = gadt; this }
+    def setFreshGADTBounds: this.type = setGadt(new GADTMap(gadt.bounds))
     def setTypeComparerFn(tcfn: Context => TypeComparer): this.type = { this.typeComparer = tcfn(this); this }
     def setSearchHistory(searchHistory: SearchHistory): this.type = { this.searchHistory = searchHistory; this }
     def setFreshNames(freshNames: FreshNameCreator): this.type = { this.freshNames = freshNames; this }
@@ -493,7 +494,6 @@ object Contexts {
     def setSetting[T](setting: Setting[T], value: T): this.type =
       setSettings(setting.updateIn(sstate, value))
 
-    def setFreshGADTBounds: this.type = { this.gadt = new GADTMap(gadt.bounds); this }
 
     def setDebug = setSetting(base.settings.debug, true)
   }
@@ -532,7 +532,7 @@ object Contexts {
     moreProperties = Map.empty
     typeComparer = new TypeComparer(this)
     searchHistory = new SearchHistory(0, Map())
-    gadt = new GADTMap(SimpleMap.Empty)
+    gadt = new GADTMap(SimpleMap.Empty) // EmptyGADTMap
   }
 
   @sharable object NoContext extends Context {
@@ -694,10 +694,13 @@ object Contexts {
     implicit val ctx: Context = initctx
   }
 
-  class GADTMap(initBounds: SimpleMap[Symbol, TypeBounds]) {
+  class GADTMap(initBounds: SimpleMap[Symbol, TypeBounds]) extends util.DotClass {
     private var myBounds = initBounds
     def setBounds(sym: Symbol, b: TypeBounds): Unit =
       myBounds = myBounds.updated(sym, b)
     def bounds = myBounds
   }
+  object EmptyGADTMap extends GADTMap(SimpleMap.Empty) {
+    override def setBounds(sym: Symbol, b: TypeBounds) = unsupported("EmptyGADTMap.setBound")
+  }
 }

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

@@ -54,17 +54,9 @@ import reporting.diagnostic.messages.SuperCallsNotAllowedInline
  *  mini-phase or subfunction of a macro phase equally well. But taken by themselves
  *  they do not warrant their own group of miniphases before pickling.
  */
-class PostTyper extends MacroTransform with SymTransformer  { thisTransformer =>
-
-
+class PostTyper extends MacroTransform with IdentityDenotTransformer { thisTransformer =>
   import tpd._
 
-  def transformSym(ref: SymDenotation)(implicit ctx: Context): SymDenotation = {
-    if (ref.is(BindDefinedType) && ctx.gadt.bounds.contains(ref.symbol)) {
-      ref.copySymDenotation(info = ctx.gadt.bounds.apply(ref.symbol) & ref.info)
-    } else ref
-  }
-
   /** the following two members override abstract members in Transform */
   override def phaseName: String = "posttyper"
 
@@ -289,6 +281,8 @@ class PostTyper extends MacroTransform with SymTransformer  { thisTransformer =>
             case _                                  =>
           }
           super.transform(tree)
+        case Typed(Ident(nme.WILDCARD), _) =>
+          tree // skip checking pattern type
         case tree =>
           super.transform(tree)
       }

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

@@ -921,16 +921,21 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
   def typedCase(tree: untpd.CaseDef, pt: Type, selType: Type, gadtSyms: Set[Symbol])(implicit ctx: Context): CaseDef = track("typedCase") {
     val originalCtx = ctx
 
+    val gadtCtx = ctx.fresh.setFreshGADTBounds
+    for (sym <- gadtSyms)
+      if (!gadtCtx.gadt.bounds.contains(sym))
+        gadtCtx.gadt.setBounds(sym, TypeBounds.empty)
+
     /** - replace all references to symbols associated with wildcards by their GADT bounds
      *  - enter all symbols introduced by a Bind in current scope
      */
     val indexPattern = new TreeMap {
       val elimWildcardSym = new TypeMap {
         def apply(t: Type) = t match {
-          case ref: TypeRef if ref.name == tpnme.WILDCARD && ctx.gadt.bounds.contains(ref.symbol) =>
-            ctx.gadt.bounds(ref.symbol)
-          case TypeAlias(ref: TypeRef) if ref.name == tpnme.WILDCARD && ctx.gadt.bounds.contains(ref.symbol) =>
-            ctx.gadt.bounds(ref.symbol)
+          case ref: TypeRef if ref.name == tpnme.WILDCARD && gadtCtx.gadt.bounds.contains(ref.symbol) =>
+            gadtCtx.gadt.bounds(ref.symbol)
+          case TypeAlias(ref: TypeRef) if ref.name == tpnme.WILDCARD && gadtCtx.gadt.bounds.contains(ref.symbol) =>
+            gadtCtx.gadt.bounds(ref.symbol)
           case _ =>
             mapOver(t)
         }
@@ -955,15 +960,6 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
       assignType(cpy.CaseDef(tree)(pat1, guard1, body1), body1)
     }
 
-    val gadtCtx =
-      if (gadtSyms.isEmpty) ctx
-      else {
-        val c = ctx.fresh.setFreshGADTBounds
-        for (sym <- gadtSyms)
-          if (!c.gadt.bounds.contains(sym))
-            c.gadt.setBounds(sym, TypeBounds.empty)
-        c
-      }
     val pat1 = typedPattern(tree.pat, selType)(gadtCtx)
     caseRest(pat1)(gadtCtx.fresh.setNewScope)
   }