Workaroud #1856: recursively calling a lazy val works differently in Dotty

Author: smarter

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

@@ -319,7 +319,17 @@ class Definitions {
     def staticsMethodRef(name: PreName) = ScalaStaticsModule.requiredMethodRef(name)
     def staticsMethod(name: PreName) = ScalaStaticsModule.requiredMethod(name)
 
-  lazy val DottyPredefModuleRef = ctx.requiredModuleRef("dotty.DottyPredef")
+  // Dotty deviation: we cannot use a lazy val here because lazy vals in dotty
+  // will return "null" when called recursively, see #1856.
+  def DottyPredefModuleRef = {
+    if (_DottyPredefModuleRef == null) {
+      _DottyPredefModuleRef = ctx.requiredModuleRef("dotty.DottyPredef")
+      assert(_DottyPredefModuleRef != null)
+    }
+    _DottyPredefModuleRef
+  }
+  private[this] var _DottyPredefModuleRef: TermRef = _
+
   def DottyPredefModule(implicit ctx: Context) = DottyPredefModuleRef.symbol
 
     def Predef_eqAny(implicit ctx: Context) = DottyPredefModule.requiredMethod(nme.eqAny)

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

@@ -30,7 +30,16 @@ object ImportInfo {
 class ImportInfo(symf: => Symbol, val selectors: List[untpd.Tree],
                  symNameOpt: Option[TermName], val isRootImport: Boolean = false)(implicit ctx: Context) {
 
-  lazy val sym = symf
+  // Dotty deviation: we cannot use a lazy val here for the same reason
+  // that we cannot use one for `DottyPredefModuleRef`.
+  def sym = {
+    if (_sym == null) {
+      _sym = symf
+      assert(_sym != null)
+    }
+    _sym
+  }
+  private[this] var _sym: Symbol = _
 
   /** The (TermRef) type of the qualifier of the import clause */
   def site(implicit ctx: Context): Type = {