Add defTree field to trees

Author: odersky

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

@@ -431,6 +431,25 @@ object Symbols {
       myCoord = c
     }
 
+    private[this] var myDefTree: Tree = null
+
+    /** The tree defining the symbol at pickler time, EmptyTree if none was retained */
+    def defTree: Tree =
+      if (myDefTree == null) tpd.EmptyTree else myDefTree
+
+    /** Set defining tree if this symbol retains its definition tree */
+    def defTree_=(tree: Tree)(implicit ctx: Context) =
+      if (retainsDefTree) myDefTree = tree
+
+    /** Does this symbol retain its definition tree?
+     *  A good policy for this needs to balance costs and benefits, where
+     *  costs are mainly memoty leaks, in particular across runs.
+     */
+    def retainsDefTree(implicit ctx: Context): Boolean =
+      ctx.settings.YretainTrees.value ||
+      denot.owner.isTerm || // no risk of leaking memory after a run for these
+      denot.is(Inline)      // need to keep inline info
+
     /** The last denotation of this symbol */
     private[this] var lastDenot: SymDenotation = _
     private[this] var checkedPeriod: Period = Nowhere

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -832,6 +832,7 @@ class TreeUnpickler(reader: TastyReader,
         // Child annotations for local classes and enum values are not pickled, so
         // need to be re-established here.
         sym.registerIfChild(late = true)
+      sym.defTree = tree
 
       if (ctx.mode.is(Mode.ReadComments)) {
         assert(ctx.docCtx.isDefined, "Mode is `ReadComments`, but no `docCtx` is set.")

compiler/src/dotty/tools/dotc/transform/PostTyper.scala

@@ -105,6 +105,7 @@ class PostTyper extends MacroTransform with IdentityDenotTransformer { thisPhase
       val sym = tree.symbol
       sym.registerIfChild()
       sym.transformAnnotations(transformAnnot)
+      sym.defTree = tree
     }
 
     private def transformSelect(tree: Select, targs: List[Tree])(implicit ctx: Context): Tree = {