Use build-in mechanism to get definitions

Author: liufengyun

compiler/src/dotty/tools/dotc/Compiler.scala

@@ -58,9 +58,8 @@ class Compiler {
          new CheckReentrant,         // Internal use only: Check that compiled program has no data races involving global vars
          new ElimPackagePrefixes,    // Eliminate references to package prefixes in Select nodes
          new CookComments,           // Cook the comments: expand variables, doc, etc.
-         new CheckStatic) ::         // Check restrictions that apply to @static members
-    List(new init.SetDefTree)   ::   // Attach trees to symbols
-    List(new init.Checker)      ::   // Check initialization of objects
+         new CheckStatic,            // Check restrictions that apply to @static members
+         new init.Checker) ::        // Check initialization of objects
     List(new CompleteJavaEnums,      // Fill in constructors for Java enums
          new ElimRepeated,           // Rewrite vararg parameters and arguments
          new ExpandSAMs,             // Expand single abstract method closures to anonymous classes

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

@@ -461,8 +461,9 @@ object Symbols {
      */
     def retainsDefTree(implicit ctx: Context): Boolean =
       ctx.settings.YretainTrees.value ||
-      denot.owner.isTerm ||        // no risk of leaking memory after a run for these
-      denot.isOneOf(InlineOrProxy)      // need to keep inline info
+      denot.owner.isTerm ||                // no risk of leaking memory after a run for these
+      denot.isOneOf(InlineOrProxy) ||      // need to keep inline info
+      ctx.settings.YcheckInit.value        // initialization check
 
     /** The last denotation of this symbol */
     private var lastDenot: SymDenotation = _

compiler/src/dotty/tools/dotc/transform/init/CheckingPhase.scala

@@ -25,7 +25,7 @@ class Checker extends MiniPhase {
   // cache of class summary
   private val baseEnv = Env(null, mutable.Map.empty)
 
-  override val runsAfter = Set(SetDefTree.name)
+  override val runsAfter = Set(Pickler.name)
 
   override def isEnabled(implicit ctx: Context): Boolean =
     super.isEnabled && ctx.settings.YcheckInit.value

compiler/src/dotty/tools/dotc/transform/init/Summarization.scala

@@ -198,6 +198,9 @@ object Summarization {
       case _: TypeDef =>
         Summary.empty
 
+      case _: Import =>
+        Summary.empty
+
       case _ =>
         throw new Exception("unexpected tree: " + expr.show)
     }