WIP: Feature/better placeholders

resolves #12 (closed)

Currently, all nonterminal classes get accompanying placeholder classes prefixed with unresolved. There are several problems with that.

• Unresolved classes are also created for types that cannot be the endpoint of a relation.
• The existence of an unresolved class means that the class must be instantiable. Even though the class is obtained by subtyping, if the superclass is abstract, there might be unimplemented abstract methods.

Therefore, two improvements are required.

1. Determine if a type can be the end point of a relation syn boolean TypeDecl.isReferenceTarget().
2. Determine if a type is instantiable at all syn boolean TypeDecl.instantiable().

These points can be checked easily. However, there is another problem. Relation endpoints can refer to types that have subtypes. However, the placeholder must still have the type of the supertype. Currently, an arbitrary instantiable subtype is selected.

• TODO: It must be made sure, that this (and only this) subtype gets a placeholder class.

src/main/jastadd/backend/NameResolution.jadd

@@ -149,7 +149,9 @@ aspect NameResolutionHelper {
     sb.append("aspect ReferenceCreation {\n\n");
 
     for (TypeDecl decl : getTypeDeclList()) {
-      decl.createReferenceCreator(sb);
+      if (decl.isReferenceTarget()) {
+        decl.createReferenceCreator(sb);
+      }
     }
 
     sb.append("}\n\n");
@@ -172,7 +174,7 @@ aspect NameResolutionHelper {
     sb.append(ind(1) + "}\n\n");
 
     for (TypeDecl td: getTypeDecls()) {
-      if (td.needUnresolvedClass()) {
+      if (td.requiresUresolvedClass()) {
         td.generateUnresolvedClass(sb);
       }
     }
@@ -182,24 +184,24 @@ aspect NameResolutionHelper {
 
   public void TypeDecl.createReferenceCreator(StringBuilder sb) {
 
-    TypeDecl instantiableSubType = instantiableSubType();
-    if (instantiableSubType == null) {
-      throw new RuntimeException("unable to find instantiable subtype for " + getID());
-    }
-
-    sb.append(ind(1) + "public static " + getID() + " " + getID() + "." + createRefMethod + "(String ref) {\n");
-      sb.append(ind(2) + unresolvedPrefix + instantiableSubType.getID() + " unresolvedNode = new " + unresolvedPrefix + instantiableSubType.getID() + "();\n");
-      sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "Token(ref);\n");
-      sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "ResolveOpposite(true);\n");
-      sb.append(ind(2) + "return unresolvedNode;\n");
-    sb.append(ind(1) + "}\n");
+    if (!instantiable()) {
+      System.out.println("WARNING: unable to find instantiable subtype for " + getID() + "! Skipping the creation of reference creator methods.");
+    } else {
+      TypeDecl instantiableSubType = instantiableSubType();
+      sb.append(ind(1) + "public static " + getID() + " " + getID() + "." + createRefMethod + "(String ref) {\n");
+        sb.append(ind(2) + unresolvedPrefix + instantiableSubType.getID() + " unresolvedNode = new " + unresolvedPrefix + instantiableSubType.getID() + "();\n");
+        sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "Token(ref);\n");
+        sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "ResolveOpposite(true);\n");
+        sb.append(ind(2) + "return unresolvedNode;\n");
+      sb.append(ind(1) + "}\n");
 
-    sb.append(ind(1) + "public static " + getID() + " " + getID() + "." + createRefDirectionMethod + "(String ref) {\n");
-      sb.append(ind(2) + unresolvedPrefix + instantiableSubType.getID() + " unresolvedNode = new " + unresolvedPrefix + instantiableSubType.getID() + "();\n");
-      sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "Token(ref);\n");
-      sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "ResolveOpposite(false);\n");
-      sb.append(ind(2) + "return unresolvedNode;\n");
-    sb.append(ind(1) + "}\n");
+      sb.append(ind(1) + "public static " + getID() + " " + getID() + "." + createRefDirectionMethod + "(String ref) {\n");
+        sb.append(ind(2) + unresolvedPrefix + instantiableSubType.getID() + " unresolvedNode = new " + unresolvedPrefix + instantiableSubType.getID() + "();\n");
+        sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "Token(ref);\n");
+        sb.append(ind(2) + "unresolvedNode.set" + unresolvedPrefix + "ResolveOpposite(false);\n");
+        sb.append(ind(2) + "return unresolvedNode;\n");
+      sb.append(ind(1) + "}\n");
+    }
   }
 
   public void TypeDecl.generateContextIndependentNameResolution(StringBuilder sb) {