More fine-grained distinctions when flags are defined.

Flags like Trait are in fact not always defined when a symbol
is created. For symbols loaded from class files, this flag, and
some other is defined only once the classfile has been loaded.
But this happens in general before the symbol is completed.

We model this distinction by separating from the `FromStartFlags` set
a new set `AfterLoadFlags` and distinguishing between the two sets
in `SymDenotations#is`.

Test case is enum-Option.scala. This erroneously complained before
that `Enum` was not a trait.

1 files changed, 9 insertions, 4 deletions

diff --git a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
index db96463e0..27782698d 100644
--- a/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/compiler/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -163,26 +163,31 @@ object SymDenotations {
       setFlag(flags & mask)
     }
 
+    private def isCurrent(fs: FlagSet) =
+      fs <= (
+        if (myInfo.isInstanceOf[SymbolLoader]) FromStartFlags
+        else AfterLoadFlags)
+
     /** Has this denotation one of the flags in `fs` set? */
     final def is(fs: FlagSet)(implicit ctx: Context) = {
-      (if (fs <= FromStartFlags) myFlags else flags) is fs
+      (if (isCurrent(fs)) myFlags else flags) is fs
     }
 
     /** Has this denotation one of the flags in `fs` set, whereas none of the flags
      *  in `butNot` are set?
      */
     final def is(fs: FlagSet, butNot: FlagSet)(implicit ctx: Context) =
-      (if (fs <= FromStartFlags && butNot <= FromStartFlags) myFlags else flags) is (fs, butNot)
+      (if (isCurrent(fs) && isCurrent(butNot)) myFlags else flags) is (fs, butNot)
 
     /** Has this denotation all of the flags in `fs` set? */
     final def is(fs: FlagConjunction)(implicit ctx: Context) =
-      (if (fs <= FromStartFlags) myFlags else flags) is fs
+      (if (isCurrent(fs)) myFlags else flags) is fs
 
     /** Has this denotation all of the flags in `fs` set, whereas none of the flags
      *  in `butNot` are set?
      */
     final def is(fs: FlagConjunction, butNot: FlagSet)(implicit ctx: Context) =
-      (if (fs <= FromStartFlags && butNot <= FromStartFlags) myFlags else flags) is (fs, butNot)
+      (if (isCurrent(fs) && isCurrent(butNot)) myFlags else flags) is (fs, butNot)
 
     /** The type info.
      *  The info is an instance of TypeType iff this is a type denotation