Adjusted grammar in spec to handle nullability token `?`.

Adjusted grammar in spec to handle nullability token `?`.

As a followup on discussions in dart-lang-evolution issue 59, here is
a proposal for grammar updates. It includes new non-terminals
`classDenotation` and `classDenotationList` (which are terms denoting
a class or a list of classes) and uses them in the locations where the
nullability token `?` is not intended to be supported. Moreover, the
non-terminal `type` is adjusted to allow a final `?`.

[eernst, 2016-09-05 15:05:12]

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

[eernst, 2016-09-05 15:05:13]

This CL adjusts the spec according to the discussions about the grammar rules
for the nullability token `?` from the discussion in
https://github.com/dart-lang/dart-lang-evolution/issues/59.

It uses `classDenotation` rather than `classLiteral` after all, because terms
like `C<int>` are essentially type-level function evaluations rather than
literals.

[Bob Nystrom, 2016-09-06 19:29:35]

rnystrom@google.com changed reviewers:
+ rnystrom@google.com

[Bob Nystrom, 2016-09-06 19:29:35]

LGTM!

Good catch on splitting up type. I didn't consider how it was used in things
like extends clauses.

[Lasse Reichstein Nielsen, 2017-05-30 10:52:30]

LGTM w/ comments (*if* we are planning to land this now!)

https://codereview.chromium.org/2316483002/diff/20001/docs/language/dartLangS...
File docs/language/dartLangSpec.tex (right):

https://codereview.chromium.org/2316483002/diff/20001/docs/language/dartLangS...
docs/language/dartLangSpec.tex:824: className typeArguments?
className is equivalent to typeName, so this could be
  typeName typeArguments?

Also, that means that type could be declared as

  type  ::= className `?'?


So, maybe rename className to typeName so:

type ::= typeName `?'?
typeName ::= type typeArguments?
type ::= qualified
typeList ::= (comma separated types)
typeNameList ::= (comma separated typeNames)

(I know that classDenotation *should* refer to a class, but that's not handled
at the syntactic level, it's just the name of a type).

https://codereview.chromium.org/2316483002/diff/20001/docs/language/dartLangS...
docs/language/dartLangSpec.tex:3420: \CONST{} classDenotation ('{\escapegrammar
.}' identifier)? arguments
' -> ` 
maybe?

https://codereview.chromium.org/2316483002/diff/20001/docs/language/dartLangS...
docs/language/dartLangSpec.tex:7054: '<' typeList '>'
The quotes here look wrong, should they be `<' and `>' ?

https://codereview.chromium.org/2316483002/diff/20001/docs/language/dartLangS...
docs/language/dartLangSpec.tex:7058: type (',' type)*
Add $\!\!$ here too?

[Bob Nystrom, 2017-06-01 23:12:25]

On 2017/05/30 10:52:30, Lasse Reichstein Nielsen wrote:
> LGTM w/ comments (*if* we are planning to land this now!)

I don't think we are, though it's nice to have it waiting in the wings.

– bob