Allow checking that trees and their defined symbols have modifiers in sync.

2 files changed, 14 insertions, 2 deletions

diff --git a/src/dotty/tools/dotc/config/ScalaSettings.scala b/src/dotty/tools/dotc/config/ScalaSettings.scala
index abde6cb53..05b936136 100644
--- a/src/dotty/tools/dotc/config/ScalaSettings.scala
+++ b/src/dotty/tools/dotc/config/ScalaSettings.scala
@@ -99,6 +99,7 @@ class ScalaSettings extends Settings.SettingGroup {
   val Yhelp = BooleanSetting("-Y", "Print a synopsis of private options.")
   val browse = PhasesSetting("-Ybrowse", "Browse the abstract syntax tree after")
   val Ycheck = PhasesSetting("-Ycheck", "Check the tree at the end of")
+  val YcheckMods = BooleanSetting("-Ycheck-mods", "Check that symbols and their defining trees have modifiers in sync")
   val YcheckTypedTrees = BooleanSetting("-YcheckTypedTrees", "Check all constructured typed trees for type correctness")
   val Yshow = PhasesSetting("-Yshow", "(Requires -Xshow-class or -Xshow-object) Show after")
   val Xcloselim = BooleanSetting("-Yclosure-elim", "Perform closure elimination.")
diff --git a/src/dotty/tools/dotc/transform/TreeChecker.scala b/src/dotty/tools/dotc/transform/TreeChecker.scala
index baaadb53f..39f4bb067 100644
--- a/src/dotty/tools/dotc/transform/TreeChecker.scala
+++ b/src/dotty/tools/dotc/transform/TreeChecker.scala
@@ -76,12 +76,23 @@ class TreeChecker {
         everDefinedSyms.get(sym) match {
           case Some(t)  =>
             if(t ne tree)
-              ctx.warning(i"symbol ${tree.symbol} is defined at least twice in different parts of AST")
+              ctx.warning(i"symbol ${sym} is defined at least twice in different parts of AST")
             // should become an error
           case None =>
             everDefinedSyms(sym) = tree
         }
-        assert(!nowDefinedSyms.contains(tree.symbol), i"doubly defined symbol: ${tree.symbol}in $tree")
+        assert(!nowDefinedSyms.contains(sym), i"doubly defined symbol: ${sym} in $tree")
+
+        if(ctx.settings.YcheckMods.value) {
+          tree match {
+            case t: MemberDef =>
+              if (t.name ne sym.name) ctx.warning(s"symbol ${sym.fullName} name doesn't correspond to AST: ${t}")
+              if (sym.flags != t.mods.flags) ctx.warning(s"symbol ${sym.fullName} flags ${sym.flags} doesn't match AST definition flags ${t.mods.flags}")
+            // todo: compare trees inside annotations
+            case _ =>
+          }
+        }
+
         nowDefinedSyms += tree.symbol
         //println(i"defined: ${tree.symbol}")
         val res = op