Allow inline metadata instantiation sans parens

[DartBot]

This issue was originally filed by @seaneagan

---

Dart supports inline instantiation of annotations, but parens are required even when there are no arguments:

@foo()
int x;

which is ugly to someone coming from Java where parens are not required, so annotation designers often create top-level constants instead. Examples:

@deprecated
@OverRide
@Proxy

This is something that would probably need to be added to the style guide to keep annotations consistent. Also, since metadata is const, the style guide currently requires these to be:

@deprecated
@OverRide
@Proxy

so they would either need to be renamed, or an exception for metadata would need to be added to the style guide. And should the constants still be created if the annotation class has optional arguments, in which case the user needs to decide which to use:

@foo
@foo()

which can't be avoided if the annotation designer wants to add optional arguments after the fact. And refactoring between the 2 forms is more difficult, since the casing of the first letter needs to change ( e.g. @­foo -> @­Foo(bar) ).

Solution:

Allow @­Foo as shorthand for @­Foo()

Then for example we could do:

@deprecated
class Foo {}

and if we wanted to use a hypothetical optional argument, we just add parens:

@deprecated(use: Bar);
class Foo {}

This would mean that if you want to use a Type literal as an annotation, you would need to first assign it to a top-level constant, but that seems like an edge case.

[sethladd]

Removed Type-Defect label.
Added Type-Enhancement, Area-Language, Triaged labels.

[DartBot]

This comment was originally written by @seaneagan

---

Mailing list discussion:

https://groups.google.com/a/dartlang.org/d/msg/misc/bZ5kVTOnUN8/y9julc1anzEJ

I filed issue #14149 for the annotation name issue raised above.

Also please see issue #13862 which is a clear consequence of this bug.

[jmesserly]

Marked this as blocking #15159.

[gbracha]

Keeping the rules uniform is always preferable in my mind. At this point the change introduces incompatibilities or more special cases: if K in metadata dart means K() in real dart, what does K() in metadata dart mean in real dart? K() or K()().

I'll leave it open in case we decide to muck with this in 2.0

---

Set owner to @gbracha.
Added Accepted label.