Enforce rules on module arguments

Author: FlandiaYingman

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

@@ -232,7 +232,32 @@ extends Importer:
       term(rhs)
     case tree @ App(lhs, rhs) =>
       val sym = FlowSymbol("‹app-res›", nextUid)
-      Term.App(term(lhs), term(rhs))(tree, sym)
+      val lt = term(lhs)
+      val rt = term(rhs)
+
+      // Check if module arguments match module parameters
+      val args = rt match
+        case Term.Tup(fields) => S(fields)
+        case _ => N
+      val params = lt.symbol
+        .filter(_.isInstanceOf[BlockMemberSymbol])
+        .flatMap(_.asInstanceOf[BlockMemberSymbol].trmTree)
+        .filter(_.isInstanceOf[TermDef])
+        .flatMap(_.asInstanceOf[TermDef].paramLists.headOption)
+      for
+        (args, params) <- (args zip params)
+        (arg, param) <- (args zip params.fields)
+      do 
+        val argMod = arg.flags.mod
+        val paramMod = param match
+          case Tree.TypeDef(Mod, _, _, _) => true
+          case _ => false
+        if !argMod && paramMod then raise:
+          ErrorReport:
+            msg"Only module arguments (values) may be passed to module parameters." -> 
+            arg.toLoc :: Nil
+      
+      Term.App(lt, rt)(tree, sym)
     case Sel(pre, nme) =>
       val preTrm = term(pre)
       val sym = resolveField(nme, preTrm.symbol, nme)

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

@@ -47,12 +47,14 @@ module N with {
 :e
 fun f6(module m: M)
 f6(new C)
-//│ FAILURE: Unexpected lack of type error
+//│ ╔══[ERROR] Only module arguments (values) may be passed to module parameters.
+//│ ║  l.49: 	f6(new C)
+//│ ╙──      	       ^
 
 :e
 fun f7(): module M
 //│ ╔══[ERROR] Only module methods may return module values.
-//│ ║  l.53: 	fun f7(): module M
+//│ ║  l.55: 	fun f7(): module M
 //│ ╙──      	    ^^^^^^^^^^^^^^