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

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

R=lrn@google.com

Committed: https://github.com/dart-lang/sdk/commit/88037f0a648e07160a078e2b9ce390c0f38c41b3

[eernst, 2016-12-16 10:06:55]

eernst@google.com changed reviewers:
+ lrn@google.com

[eernst, 2016-12-16 10:06:55]

I couldn't find these errors in the spec, aren't they missing?

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

LGTM, but should it also cover mixins ("with")?

https://codereview.chromium.org/2585723002/diff/1/docs/language/dartLangSpec.tex
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/2585723002/diff/1/docs/language/dartLangSpec....
docs/language/dartLangSpec.tex:1784: %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 $C$.
Remove the comment, and the one below.

https://codereview.chromium.org/2585723002/diff/1/docs/language/dartLangSpec....
docs/language/dartLangSpec.tex:1924: It is a compile-time error if the
superclass of a class $C$ is specified as a superinterface of $C$.
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]

Review response, PTAL.

https://codereview.chromium.org/2585723002/diff/1/docs/language/dartLangSpec.tex
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/2585723002/diff/1/docs/language/dartLangSpec....
docs/language/dartLangSpec.tex:1784: %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 $C$.
On 2016/12/16 11:14:59, Lasse Reichstein Nielsen wrote:
> Remove the comment, and the one below.

Done.

https://codereview.chromium.org/2585723002/diff/1/docs/language/dartLangSpec....
docs/language/dartLangSpec.tex:1924: It is a compile-time error if the
superclass of a class $C$ is specified as a superinterface of $C$.
On 2016/12/16 11:14:59, Lasse Reichstein Nielsen wrote:
> 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?

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.

[Lasse Reichstein Nielsen, 2016-12-16 12:12:02]

LGTM

https://codereview.chromium.org/2585723002/diff/20001/docs/language/dartLangS...
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/2585723002/diff/20001/docs/language/dartLangS...
docs/language/dartLangSpec.tex:2099: It is a compile-time error if the \WITH{}
clause of a mixin application $C$ includes a type variable (\ref{generics}), a
type alias (\ref{typedef}), an enumerated type (\ref{enums}), a malformed type,
or a deferred type (\ref{staticTypes}).
It would be much easier if we had a definition of "class type" somewhere, so we
could just say "error ... if ... not class type". :)

[eernst, 2016-12-16 13:03:29]

Description was changed from

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

to

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

R=lrn@google.com

Committed:
https://github.com/dart-lang/sdk/commit/88037f0a648e07160a078e2b9ce390c0f38c41b3
==========

[eernst, 2016-12-16 13:03:31]

Committed patchset #2 (id:20001) manually as
88037f0a648e07160a078e2b9ce390c0f38c41b3 (presubmit successful).

[eernst, 2016-12-16 13:06:05]

Review response.

https://codereview.chromium.org/2585723002/diff/20001/docs/language/dartLangS...
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/2585723002/diff/20001/docs/language/dartLangS...
docs/language/dartLangSpec.tex:2099: It is a compile-time error if the \WITH{}
clause of a mixin application $C$ includes a type variable (\ref{generics}), a
type alias (\ref{typedef}), an enumerated type (\ref{enums}), a malformed type,
or a deferred type (\ref{staticTypes}).
On 2016/12/16 12:12:02, Lasse Reichstein Nielsen wrote:
> It would be much easier if we had a definition of "class type" somewhere, so
we
> could just say "error ... if ... not class type". :)

Right, which was basically what Gilad already had in that commented-out sentence
that I just deleted. I wonder why he dropped that approach?