Added compile-time errors for supertypes: Type alias missing, and more.

docs/language/dartLangSpec.tex

Index: docs/language/dartLangSpec.tex
diff --git a/docs/language/dartLangSpec.tex b/docs/language/dartLangSpec.tex
index 44e846cf68a64ec44684977b2179c3719e95b50b..94510502bac9143a810538c7a132adef14cd62f7 100644
--- a/docs/language/dartLangSpec.tex
+++ b/docs/language/dartLangSpec.tex
@@ -1782,7 +1782,8 @@ The scope of the \EXTENDS{} and \WITH{} clauses of a class $C$ is the type-param
 
 \LMHash{}
 %It is a compile-time error if  the \EXTENDS{} clause of a class $C$ includes a type expression that does not denote a class available in the lexical scope of $C$.

[Lasse Reichstein Nielsen, 2016/12/16 11:14:59]

Remove the comment, and the one below.

[eernst, 2016/12/16 11:33:47]

Done.

-It is a compile-time error if  the \EXTENDS{} clause of a class $C$ specifies an enumerated type (\ref{enums}), a malformed  type or a deferred type (\ref{staticTypes}) as a superclass.
+It is a compile-time error if the \EXTENDS{} clause of a class $C$ specifies a type variable (\ref{generics}), a type alias (\ref{typedef}), an enumerated type (\ref{enums}), a malformed type, or a deferred type (\ref{staticTypes}) as a superclass.
+It is a compile-time error if the \EXTENDS{} clause of a class $C$ specifies type \DYNAMIC{} as a superinterface.
 % too strict? Do we e want extends List<Undeclared> to work as List<dynamic>?
 
 \commentary{ The type parameters of a generic class are available in the lexical scope of the superclass clause, potentially shadowing classes in the surrounding scope. The following code is therefore illegal and should cause a compile-time error:
@@ -1917,7 +1918,9 @@ A class has a set of direct superinterfaces. This set includes the interface of
 The scope of the \IMPLEMENTS{} clause of a class $C$ is the type-parameter scope of $C$.
 
 \LMHash{}
-It is a compile-time error if  the \IMPLEMENTS{}  clause of a class $C$ specifies a type variable as a superinterface. It is a compile-time error if  the  \IMPLEMENTS{} clause of a class $C$ specifies an enumerated type (\ref{enums}),  a malformed type or deferred type (\ref{staticTypes}) as a superinterface.  It is a compile-time error if the \IMPLEMENTS{} clause of a class $C$ specifies type \DYNAMIC{} as a superinterface. It is a compile-time error if  the  \IMPLEMENTS{} clause of a class $C$ specifies  a type $T$ as a superinterface more than once.
+It is a compile-time error if the \IMPLEMENTS{} clause of a class $C$ specifies a type variable (\ref{generics}), a type alias (\ref{typedef}), an enumerated type (\ref{enums}), a malformed type, or a deferred type (\ref{staticTypes}) as a superinterface.
+It is a compile-time error if the \IMPLEMENTS{} clause of a class $C$ specifies type \DYNAMIC{} as a superinterface.
+It is a compile-time error if the \IMPLEMENTS{} clause of a class $C$ specifies a type $T$ as a superinterface more than once.
 It is a compile-time error if the superclass of a class $C$ is specified as a superinterface of $C$.

[Lasse Reichstein Nielsen, 2016/12/16 11:14:59]

How does this sentence interact with mixins?
That is: class X extends C with M implements C {}
Here, C is an interface but the superclass isn't C, it's C-with-M. Is that
intended to not give an error, while `class Y extends C implements C` errs?

[eernst, 2016/12/16 11:33:47]

Good question!

As stated below, we could really just let it pass (in all cases, or some,
whatever we want), and it won't matter much whether we insist on more errors in
this area: Should we prevent `implements` on something which is already
implemented indirectly? or on something which is implemented indirectly, because
it is already implemented indirectly via some other supertype? I think the
answer must clearly be no in the latter case ("overlapping supertypes among
direct supertypes") so I'm in favor of letting this be a rather stupid rule, and
say "`class X extends C with M implements C {}` is OK", simply because we don't
want to go all the way anyway.

 
 \rationale{