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

2 files changed, 21 insertions, 2 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/Definitions.scala b/compiler/src/dotty/tools/dotc/core/Definitions.scala
index 134b31519..0aeb28d36 100644
--- a/compiler/src/dotty/tools/dotc/core/Definitions.scala
+++ b/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 (myDottyPredefModuleRef == null) {
+      myDottyPredefModuleRef = ctx.requiredModuleRef("dotty.DottyPredef")
+      assert(myDottyPredefModuleRef != null)
+    }
+    myDottyPredefModuleRef
+  }
+  private[this] var myDottyPredefModuleRef: TermRef = _
+
   def DottyPredefModule(implicit ctx: Context) = DottyPredefModuleRef.symbol
 
     def Predef_eqAny(implicit ctx: Context) = DottyPredefModule.requiredMethod(nme.eqAny)
diff --git a/compiler/src/dotty/tools/dotc/typer/ImportInfo.scala b/compiler/src/dotty/tools/dotc/typer/ImportInfo.scala
index a5657890e..f7efb2ac2 100644
--- a/compiler/src/dotty/tools/dotc/typer/ImportInfo.scala
+++ b/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 (mySym == null) {
+      mySym = symf
+      assert(mySym != null)
+    }
+    mySym
+  }
+  private[this] var mySym: Symbol = _
 
   /** The (TermRef) type of the qualifier of the import clause */
   def site(implicit ctx: Context): Type = {