Split out immutable GadtConstraint

Author: dwijnand

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

@@ -71,6 +71,9 @@ abstract class Constraint extends Showable {
    */
   def nonParamBounds(param: TypeParamRef)(using Context): TypeBounds
 
+  /** The current bounds of type parameter `param` */
+  def bounds(param: TypeParamRef)(using Context): TypeBounds
+
   /** A new constraint which is derived from this constraint by adding
    *  entries for all type parameters of `poly`.
    *  @param tvars   A list of type variables associated with the params,

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

@@ -749,16 +749,7 @@ trait ConstraintHandling {
     }
 
   /** The current bounds of type parameter `param` */
-  def bounds(param: TypeParamRef)(using Context): TypeBounds = {
-    val e = constraint.entry(param)
-    if (e.exists) e.bounds
-    else {
-      // TODO: should we change the type of paramInfos to nullable?
-      val pinfos: List[param.binder.PInfo] | Null = param.binder.paramInfos
-      if (pinfos != null) pinfos(param.paramNum) // pinfos == null happens in pos/i536.scala
-      else TypeBounds.empty
-    }
-  }
+  def bounds(param: TypeParamRef)(using Context): TypeBounds = constraint.bounds(param)
 
   /** Add type lambda `tl`, possibly with type variables `tvars`, to current constraint
    *  and propagate all bounds.

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

@@ -141,7 +141,7 @@ object Contexts {
     def tree: Tree[?]
     def scope: Scope
     def typerState: TyperState
-    def gadt: GadtConstraint
+    def gadt: GadtConstraintHandling
     def searchHistory: SearchHistory
     def source: SourceFile
 
@@ -539,8 +539,8 @@ object Contexts {
     private var _typerState: TyperState = uninitialized
     final def typerState: TyperState = _typerState
 
-    private var _gadt: GadtConstraint = uninitialized
-    final def gadt: GadtConstraint = _gadt
+    private var _gadt: GadtConstraintHandling = uninitialized
+    final def gadt: GadtConstraintHandling = _gadt
 
     private var _searchHistory: SearchHistory = uninitialized
     final def searchHistory: SearchHistory = _searchHistory
@@ -622,7 +622,7 @@ object Contexts {
       this._scope = typer.scope
       setTypeAssigner(typer)
 
-    def setGadt(gadt: GadtConstraint): this.type =
+    def setGadt(gadt: GadtConstraintHandling): this.type =
       util.Stats.record("Context.setGadt")
       this._gadt = gadt
       this
@@ -719,7 +719,7 @@ object Contexts {
           .updated(notNullInfosLoc, Nil)
           .updated(compilationUnitLoc, NoCompilationUnit)
       c._searchHistory = new SearchRoot
-      c._gadt = GadtConstraint.empty
+      c._gadt = GadtConstraintHandling(GadtConstraint.empty)
       c
   end FreshContext