Avoid eager forcing in enterArgBinding

Caused a cyclic reference error when compiling the three files in test "testNonCyclic".

Author: odersky

src/dotty/tools/dotc/config/Printers.scala

@@ -15,7 +15,7 @@ object Printers {
   val typr: Printer = new Printer
   val constr: Printer = noPrinter
   val overload: Printer = noPrinter
-  val implicits: Printer = new Printer
+  val implicits: Printer = noPrinter
   val unapp: Printer = noPrinter
   val completions = noPrinter
   val gadts = noPrinter

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

@@ -128,10 +128,9 @@ object SymDenotations {
       if (myFlags is Touched) throw new CyclicReference(this)
       myFlags |= Touched
 
-      Context.theBase.initialCtx.traceIndented(s"completing ${this.debugString}", completions) {
-        // println("completing " + debugString)
-        completer.complete(this)
-      }
+      completions.println(s"completing ${this.debugString}")
+      completer.complete(this)
+      completions.println(s"completed ${this.debugString}")
     }
 
     protected[dotc] final def info_=(tp: Type) = {

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

@@ -2,6 +2,7 @@ package dotty.tools.dotc
 package core
 
 import Contexts._, Types._, Symbols._, Names._, Flags._, Scopes._
+import SymDenotations._
 import util.SimpleMap
 
 trait TypeOps { this: Context =>
@@ -86,8 +87,14 @@ trait TypeOps { this: Context =>
   }
 
   private def enterArgBinding(formal: Symbol, info: Type, cls: ClassSymbol, decls: Scope) = {
+    val lazyInfo = new LazyType { // needed so we do not force `formal`.
+      def complete(denot: SymDenotation): Unit = {
+        denot setFlag formal.flags & RetainedTypeArgFlags
+        denot.info = info
+      }
+    }
     val typeArgFlag = if (formal is Local) TypeArgument else EmptyFlags
-    val sym = ctx.newSymbol(cls, formal.name, formal.flags & RetainedTypeArgFlags | typeArgFlag, info)
+    val sym = ctx.newSymbol(cls, formal.name, formal.flagsUNSAFE & RetainedTypeArgFlags | typeArgFlag, lazyInfo)
     cls.enter(sym, decls)
   }
 

test/dotc/tests.scala

@@ -57,6 +57,12 @@ class tests extends CompilerTest {
   @Test def tools_io = compileDir(dotcDir + "tools/io")
   @Test def tools = compileDir(dotcDir + "tools")
 
-  @Test def dotc_compilercommand = compileFile(dotcDir + "tools/dotc/config/", "CompilerCommand")
+  @Test def testNonCyclic = compileArgs(Array(
+      dotcDir + "tools/dotc/CompilationUnit.scala",
+      dotcDir + "tools/dotc/core/Types.scala",
+      dotcDir + "tools/dotc/ast/Trees.scala",
+      "-Ylog:frontend",
+      "-Xprompt"))
 
+  //@Test def dotc_compilercommand = compileFile(dotcDir + "tools/dotc/config/", "CompilerCommand")
 }