Fix Ycheck: allow assigning fields in static constructors.

Author: DarkDimius

src/dotty/tools/dotc/core/NameOps.scala

@@ -63,6 +63,7 @@ object NameOps {
       (if (name.isTermName) n.toTermName else n.toTypeName).asInstanceOf[N]
 
     def isConstructorName = name == CONSTRUCTOR || name == TRAIT_CONSTRUCTOR
+    def isStaticConstructorName = name == STATIC_CONSTRUCTOR
     def isExceptionResultName = name startsWith EXCEPTION_RESULT_PREFIX
     def isImplClassName = name endsWith IMPL_CLASS_SUFFIX
     def isLocalDummyName = name startsWith LOCALDUMMY_PREFIX

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

@@ -594,6 +594,10 @@ object SymDenotations {
     final def isPrimaryConstructor(implicit ctx: Context) =
       isConstructor && owner.primaryConstructor == symbol
 
+    /** Does this symbol denote the primary constructor of its enclosing class? */
+    final def isStaticConstructor(implicit ctx: Context) =
+      name.isStaticConstructorName
+
     /** Is this a subclass of the given class `base`? */
     def isSubClass(base: Symbol)(implicit ctx: Context) = false
 

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

@@ -476,7 +476,7 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
         def canAssign(sym: Symbol) = // allow assignments from the primary constructor to class fields
           sym.is(Mutable, butNot = Accessor) ||
           ctx.owner.isPrimaryConstructor && !sym.is(Method) && sym.owner == ctx.owner.owner ||
-          ctx.owner.name.isTraitSetterName
+          ctx.owner.name.isTraitSetterName || ctx.owner.isStaticConstructor
         lhsCore.tpe match {
           case ref: TermRef if canAssign(ref.symbol) =>
             assignType(cpy.Assign(tree)(lhs1, typed(tree.rhs, ref.info)))