A class/interface cannot implement/extend a type parameter (issues 886 and 887).

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 3103)
+++ runtime/vm/parser.cc	(working copy)
@@ -2512,7 +2512,13 @@
   Type& super_type = Type::Handle();
   if (CurrentToken() == Token::kEXTENDS) {
     ConsumeToken();
-    super_type ^= ParseType(kCanResolve);
+    const AbstractType& type = AbstractType::Handle(ParseType(kCanResolve));
+    if (type.IsTypeParameter()) {
+      ErrorMsg("class '%s' may not extend type parameter '%s'",

[hausner, 2012/01/09 18:54:49]

I would print the error at the actual text position of the type. You can
remember the token position after consuming the 'extends' token.

[regis, 2012/01/09 19:19:30]

Done here and on line 2523 below.

+               class_name.ToCString(),
+               String::Handle(type.Name()).ToCString());
+    }
+    super_type ^= type.raw();
     if (super_type.IsInterfaceType()) {
       ErrorMsg("class '%s' may implement, but cannot extend interface '%s'",
                class_name.ToCString(),
@@ -3004,6 +3010,17 @@
   for (intptr_t i = 0; i < interfaces.Length(); i++) {
     AbstractType& interface = AbstractType::ZoneHandle();
     interface ^= interfaces.At(i);
+    if (interface.IsTypeParameter()) {
+      if (cls.is_interface()) {
+        ErrorMsg("interface '%s' may not extend type parameter '%s'",

[hausner, 2012/01/09 18:54:49]

Would be nice if these error messages were pointing to the actual interface name
that causes the error. At least though I would print the error at interface_pos,
like in the error message at line 3028.

[regis, 2012/01/09 19:19:30]

We should definitely store the position in each type. For now, I use
interface_pos, as you suggested.

+                 String::Handle(cls.Name()).ToCString(),
+                 String::Handle(interface.Name()).ToCString());
+      } else {
+        ErrorMsg("class '%s' may not implement type parameter '%s'",
+                 String::Handle(cls.Name()).ToCString(),
+                 String::Handle(interface.Name()).ToCString());
+      }
+    }
     if (!ClassFinalizer::AddInterfaceIfUnique(&all_interfaces,
                                               &interface,
                                               &conflicting)) {