This finally fixes a few code completion test cases.
This also regresses the error message in one parsing testcase because
previously we would just happily skip those tokens, but now error handling path
is a little bit different and these tokens hit different error handling code.
This can be fixed by parsing a tuple for the selector argument and complaining
if the tuple had more than one element.
Swift SVN r7389
This will allow us to do code completion inside lists (e.g., tuples) *and* get
parser recovery instead of stopping at the code completion token immediately.
Swift SVN r7366
This allows the parser to recover, create an AST node, return it to the caller
*and* signal the caller that there was an error to trigger recovery in the
caller. Until now the error was signalled with a nullptr result (any non-null
result was considered a success and no recovery was done in that case).
This also allows us to signal the caller if there was a code completion token
inside the production we tried to parse to trigger delayed parsing in the
caller while doing recovery in the callee. Until now we could not do recovery
in the callee so that the caller could find the code completion token.
Right now we don't take any advantage of these features. This commit just
replaces some uses of NullablePtr with ParserResult.
Swift SVN r7332
