https://github.com/manifold-systems/manifold/issues/584

- changes that may help diagnose this issue

Author: rsmckinney

manifold-core-parent/manifold-rt/src/main/java/manifold/rt/api/util/TypesUtil.java

@@ -47,7 +47,7 @@ static boolean isStructuralInterface( Types types, Symbol sym )
 
     for( Attribute.Compound annotation : sym.getAnnotationMirrors() )
     {
-      if( annotation.type.toString().equals( STRUCTURAL ) )
+      if( annotation.type != null && annotation.type.toString().equals( STRUCTURAL ) )
       {
         return true;
       }

manifold-core-parent/manifold/src/main/java/manifold/internal/javac/ManTypes.java

@@ -30,6 +30,19 @@ public interface ManTypes
    * Note, this tests the _erased_ types of t and s. Handling generics here is a bridge too for, for now.
    */
   default boolean isAssignableToStructuralType( Type t, Type s )
+  {
+    try
+    {
+      return _isAssignableToStructuralType( t, s );
+    }
+    catch( Throwable e )
+    {
+      // todo: diagnose this
+      //  as a diagnostic, prevent this check from causing an exception to quietly test if it is causing compilation failure
+      return false;
+    }
+  }
+  default boolean _isAssignableToStructuralType( Type t, Type s )
   {
     t = types().erasure( t );
     s = types().erasure( s );

manifold-core-parent/manifold/src/main/java/manifold/internal/javac/ManTypes_17.java17

@@ -525,6 +525,7 @@ public class ManTypes_17 extends Types implements ManTypes
     {
       return true;
     }
+
     return super.returnTypeSubstitutable( r1, r2, r2res, warner );
   }
 
@@ -552,14 +553,10 @@ public class ManTypes_17 extends Types implements ManTypes
     return super.isConvertible( t, s, warn );
   }
 
-  public boolean isSubtype(Type t, Type s, boolean capture)
+  public boolean isSubtype( Type t, Type s, boolean capture )
   {
-    if( isAssignableToStructuralType( t, s ) )
-    {
-      return true;
-    }
-
-    return super.isSubtype(t, s, capture);
+    return super.isSubtype( t, s, capture ) ||
+      isAssignableToStructuralType( t, s );
   }
 
   @Override

manifold-core-parent/manifold/src/main/java/manifold/internal/javac/ManTypes_8.java

@@ -550,13 +550,8 @@ public boolean isConvertible( Type t, Type s, Warner warn )
 
   public boolean isSubtype( Type t, Type s, boolean capture )
   {
-    if( isAssignableToStructuralType( t, s ) )
-    {
-      // t is structurally assignable to s
-      return true;
-    }
-
-    return super.isSubtype(t, s, capture);
+    return super.isSubtype( t, s, capture ) ||
+      isAssignableToStructuralType( t, s );
   }
 
   @Override