Raw identifiers are backtick-delimited identifiers that can contain any
non-identifier character other than the backtick itself, CR, LF, or other
non-printable ASCII code units, and which are also not composed entirely
of operator characters.
Always parse macro expansions, regardless of language mode, and
eliminate the fallback path for very, very, very old object literals
like `#Color`. Instead, check for the feature flag for macro
declaration and at macro expansion time, since this is a semantic
restriction.
While here, refactor things so the vast majority of the macro-handling
logic still applies even if the Swift Swift parser is disabled. Only
attempts to expand the macro will fail. This allows us to enable the
macro-diagnostics test everywhere.
Instead, check them and their error handling right away.
In addition to fixing the crash in the radar, this also causes
us to emit unused variable warnings in functions containing
local functions.
Eventually, TC.definedFunctions should go away altogether.
Fixes <rdar://problem/53956342>.
Allow the use of declarations whose names start with $ in all
modes. However, normal code cannot define new entities with names that
start with $: only the implementation can do that, e.g., for property
delegates.
When in Swift 3 Compatibility Mode we now acceptable a standalone
'$' as an identifier. In all other cases this is now disallowed
and must be surrounded by backticks.
