Separate module methods from regular methods

Module definitions were implemented by a `ClassDef` with the `kind` being set to `Mod`, despite the existence of `ModuleDef`. Therefore, a module definition would even have a `ClassSymbol` rather than a `ModuleSymbol`!

This commit separates `ModuleDef` from `ClassDef`: modules will be elaborated into `ModuleDef` instead of `ClassDef`, with the `kind` of `Mod` and `ModuleSymbol`. This may break the code generator.

Author: FlandiaYingman

hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala

@@ -471,6 +471,7 @@ extends Importer:
           case R(id) =>
             val sym = members.getOrElse(id.name, die)
             val owner = ctx.outer
+            val mod = owner.fold(false)(_.isInstanceOf[ModuleSymbol])
             val tdf = ctx.nest(N).givenIn:
               // * Add type parameters to context
               val (tps, newCtx1) = td.typeParams match
@@ -486,7 +487,7 @@ extends Importer:
               val r = FlowSymbol(s"‹result of ${sym}›", nextUid)
               val tdf = TermDefinition(owner, k, sym, pss,
                 td.signature.orElse(newSignatureTrees.get(id.name)).map(term), b, r,
-                TermDefFlags.empty)
+                TermDefFlags(mod))
               sym.defn = S(tdf)
               tdf
             go(sts, tdf :: acc)

hkmc2/shared/src/test/mlscript/basics/ModuleMethods.mls

@@ -63,7 +63,7 @@ module M with {
 //│             sign = N
 //│             body = S of Ref of x@31
 //│             resSym = ‹result of member:foo›@32
-//│             flags = ()
+//│             flags = (module)
 //│         res = Lit of UnitLit of true
 //│   res = Lit of UnitLit of true
 
@@ -299,13 +299,13 @@ fun idMod[T](t: MT[T]): MT[T] = t
 //│ FAILURE: Unexpected exception
 //│ /!!!\ Uncaught error: scala.NotImplementedError: an implementation is missing
 //│ 	at: scala.Predef$.$qmark$qmark$qmark(Predef.scala:344)
-//│ 	at: hkmc2.semantics.Elaborator$VarianceTraverser.traverseType(Elaborator.scala:707)
-//│ 	at: hkmc2.semantics.Elaborator$Traverser.traverseType$$anonfun$10(Elaborator.scala:749)
+//│ 	at: hkmc2.semantics.Elaborator$VarianceTraverser.traverseType(Elaborator.scala:708)
+//│ 	at: hkmc2.semantics.Elaborator$Traverser.traverseType$$anonfun$10(Elaborator.scala:750)
 //│ 	at: scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
 //│ 	at: scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
 //│ 	at: scala.Option.foreach(Option.scala:437)
-//│ 	at: hkmc2.semantics.Elaborator$Traverser.traverseType(Elaborator.scala:749)
-//│ 	at: hkmc2.semantics.Elaborator.go$4$$anonfun$1$$anonfun$1(Elaborator.scala:659)
+//│ 	at: hkmc2.semantics.Elaborator$Traverser.traverseType(Elaborator.scala:750)
+//│ 	at: hkmc2.semantics.Elaborator.go$4$$anonfun$1$$anonfun$1(Elaborator.scala:660)
 //│ 	at: scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
 //│ 	at: scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)