[Parse] Skip attributes in isStartOfDecl().

[rintaro]

Previously, @ token was unconditionally considered as isStartOfDecl()

Since canParseTypeTupleBody() fails at isStartOfDecl(),
generic argument containing type attributes, e.g.
Array<(@convention(block) () -> Int) -> Void>
failed to be parsed.

[rintaro]

Alternatively, can we simply drop isStartOfDecl() check in canParseTypeTupleBody()?
That passes all test cases we currently have.

[DougGregor]

This change looks great.

I think the Parser::canParseTypeTupleBody code you referenced is trying to prevent tentative parsing from going off the rails in ill-formed code. It's probably better to leave it.

[rintaro]

@swift-ci Please smoke test and merge

[rintaro]

Sorry, I should have throughly tested locally 😓
The failures are because this change can't handle these cases.

@ [code_complete]
func foo() {}

  @something(incomplete
  func foo() { }
}

[rintaro]

@swift-ci Please smoke test

[rintaro]

@DougGregor Sorry to bother you. Could you take a look again?
Updated the skipping logic.

[DougGregor]

This revision LGTM, thanks!

[rintaro]

@swift-ci Please smoke test and merge