fix: disallow unknown type assignments and reads

src/main/wacc/typeChecker.scala

@@ -99,12 +99,30 @@ object typeChecker {
       )
     case Assign(lhs, rhs) =>
       val lhsTy = checkValue(lhs, Constraint.Unconstrained)
-      checkValue(rhs, Constraint.Is(lhsTy, s"assignment must have type $lhsTy"))
-    case Read(lhs) =>
-      checkValue(
-        lhs,
-        Constraint.IsEither(KnownType.Int, KnownType.Char, "read must be int or char")
+      checkValue(rhs, Constraint.Is(lhsTy, s"assignment must have type $lhsTy")) match {
+        case ? =>
+          ctx.error(
+            Error.SemanticError(lhs.pos, "assignment with both sides of unknown type is illegal")
           )
+        case _ => ()
+      }
+    case Read(lhs) =>
+      val lhsTy = checkValue(lhs, Constraint.Unconstrained)
+      lhsTy match {
+        case ? =>
+          ctx.error(
+            Error.SemanticError(lhs.pos, "cannot read into a destination with an unknown type")
+          )
+        case _ =>
+          lhsTy.satisfies(
+            Constraint.IsEither(
+              KnownType.Int,
+              KnownType.Char,
+              "read must be applied to an int or char"
+            ),
+            lhs.pos
+          )
+      }
     case Free(lhs) =>
       checkValue(
         lhs,
@@ -193,7 +211,8 @@ object typeChecker {
         elem,
         Constraint.Is(KnownType.Pair(?, ?), "fst must be applied to a pair")
       ) match {
-        case KnownType.Pair(left, _) => left.satisfies(constraint, elem.pos)
+        case what @ KnownType.Pair(left, _) =>
+          left.satisfies(constraint, elem.pos)
         case ? => ?.satisfies(constraint, elem.pos)
         case _ => ctx.error(Error.InternalError(elem.pos, "fst must be applied to a pair"))
       } // satisfies constraint

src/test/wacc/examples.scala

@@ -16,7 +16,7 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
         (p.toString, List(200))
       } ++
       allWaccFiles("wacc-examples/invalid/whack").map { p =>
-        (p.toString, List(0, 100, 200))
+        (p.toString, List(100, 200))
       }
 
   // tests go here
@@ -82,7 +82,7 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
       // "wacc-examples/invalid/semanticErr/variables",
       // "wacc-examples/invalid/semanticErr/while",
       // invalid (whack)
-      "wacc-examples/invalid/whack"
+      // "wacc-examples/invalid/whack"
       // format: on
       // format: on
     ).find(filename.contains).isDefined