Fix #2924: make TreeChecker.typedBlock iterative

Author: nicolasstucki

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

@@ -149,34 +149,42 @@ class TreeChecker extends Phase with SymTransformer {
 
     def withDefinedSym[T](tree: untpd.Tree)(op: => T)(implicit ctx: Context): T = tree match {
       case tree: untpd.DefTree =>
-        val sym = tree.symbol
-        assert(isValidJVMName(sym.name.encode), s"${sym.name.debugString} name is invalid on jvm")
-        everDefinedSyms.get(sym) match {
-          case Some(t)  =>
-            if (t ne tree)
-              ctx.warning(i"symbol ${sym.fullName} is defined at least twice in different parts of AST")
-            // should become an error
-          case None =>
-            everDefinedSyms(sym) = tree
-        }
-        assert(!nowDefinedSyms.contains(sym), i"doubly defined symbol: ${sym.fullName} in $tree")
-
-        if (ctx.settings.YcheckMods.value) {
-          tree match {
-            case t: untpd.MemberDef =>
-              if (t.name ne sym.name) ctx.warning(s"symbol ${sym.fullName} name doesn't correspond to AST: ${t}")
-            // todo: compare trees inside annotations
-            case _ =>
-          }
+        preWithDefinedSym(tree)
+        postWithDefinedSym(tree)(op)
+      case _ => op
+    }
+
+    private def preWithDefinedSym[T](tree: untpd.DefTree)(implicit ctx: Context): Unit = {
+      val sym = tree.symbol
+      assert(isValidJVMName(sym.name.encode), s"${sym.name.debugString} name is invalid on jvm")
+      everDefinedSyms.get(sym) match {
+        case Some(t)  =>
+          if (t ne tree)
+            ctx.warning(i"symbol ${sym.fullName} is defined at least twice in different parts of AST")
+        // should become an error
+        case None =>
+          everDefinedSyms(sym) = tree
+      }
+      assert(!nowDefinedSyms.contains(sym), i"doubly defined symbol: ${sym.fullName} in $tree")
+
+      if (ctx.settings.YcheckMods.value) {
+        tree match {
+          case t: untpd.MemberDef =>
+            if (t.name ne sym.name) ctx.warning(s"symbol ${sym.fullName} name doesn't correspond to AST: ${t}")
+          // todo: compare trees inside annotations
+          case _ =>
         }
+      }
+    }
 
-        nowDefinedSyms += tree.symbol
-        //ctx.echo(i"defined: ${tree.symbol}")
-        val res = op
-        nowDefinedSyms -= tree.symbol
-        //ctx.echo(i"undefined: ${tree.symbol}")
-        res
-      case _ => op
+    private def postWithDefinedSym[T](tree: untpd.DefTree)(op: => T)(implicit ctx: Context): T = {
+      val sym = tree.symbol
+      nowDefinedSyms += sym
+      //ctx.echo(i"defined: ${tree.symbol}")
+      val res = op
+      nowDefinedSyms -= sym
+      //ctx.echo(i"undefined: ${tree.symbol}")
+      res
     }
 
     def withDefinedSyms[T](trees: List[untpd.Tree])(op: => T)(implicit ctx: Context) =
@@ -411,8 +419,21 @@ class TreeChecker extends Phase with SymTransformer {
       }
     }
 
-    override def typedBlock(tree: untpd.Block, pt: Type)(implicit ctx: Context) =
-      withDefinedSyms(tree.stats) { super.typedBlock(tree, pt) }
+    override def typedBlock(tree: untpd.Block, pt: Type)(implicit ctx: Context) = {
+      var locally = List.empty[Symbol]
+      for (stat <- tree.stats) {
+        stat match {
+          case stat: untpd.DefTree =>
+            preWithDefinedSym(stat)
+            locally = stat.symbol :: locally
+            nowDefinedSyms += stat.symbol
+          case _ =>
+        }
+      }
+      val res = super.typedBlock(tree, pt)
+      nowDefinedSyms --= locally
+      res
+    }
 
     override def typedInlined(tree: untpd.Inlined, pt: Type)(implicit ctx: Context) =
       withDefinedSyms(tree.bindings) { super.typedInlined(tree, pt) }