Implement 'rethrows' checking in Sema.

Now with amazing new fixes and tests for methods and generics!

Swift SVN r28499

Author: rjmccall

include/swift/AST/DiagnosticsSema.def

@@ -1798,13 +1798,30 @@ ERROR(isa_pattern_value,sema_tcp,none,
 
 ERROR(try_unhandled,sema,none,
       "errors thrown from here are not handled", ())
+ERROR(throwing_call_unhandled,sema,none,
+      "call can throw, but the error is not handled", ())
 ERROR(tryless_throwing_call_unhandled,sema,none,
       "call can throw, but it is not marked with 'try' and "
       "the error is not handled", ())
 ERROR(throw_in_nonthrowing_function,sema,none,
       "error is not handled because the enclosing function "
       "is not declared 'throws'", ())
 
+ERROR(throwing_call_in_rethrows_function,sema,none,
+      "throwing call in 'rethrows' function is not to a parameter "
+      "function", ())
+ERROR(tryless_throwing_call_in_rethrows_function,sema,none,
+      "throwing call in 'rethrows' function is not to a parameter "
+      "function and is not marked with 'try'", ())
+ERROR(throw_in_rethrows_function,sema,none,
+      "'rethrows' function may only throw by calling a parameter "
+      "function", ())
+NOTE(because_rethrows_argument_throws,sema,none,
+     "call is to 'rethrows' function, but argument function can throw", ())
+NOTE(because_rethrows_default_argument_throws,sema,none,
+     "call is to 'rethrows' function, but a defaulted argument function"
+     " can throw", ())
+
 ERROR(throwing_call_in_nonthrowing_autoclosure,sema,none,
       "call can throw, but it is executed in a non-throwing "
       "autoclosure",())
@@ -1818,11 +1835,11 @@ ERROR(throw_in_nonthrowing_autoclosure,sema,none,
 ERROR(try_unhandled_in_nonexhaustive_catch,sema,none,
       "errors thrown from here are not handled because the "
       "enclosing catch is not exhaustive", ())
+ERROR(throwing_call_in_nonexhaustive_catch,sema,none,
+      "call can throw, but the enclosing catch is not exhaustive", ())
 ERROR(tryless_throwing_call_in_nonexhaustive_catch,sema,none,
       "call can throw, but it is not marked with 'try' and "
       "the enclosing catch is not exhaustive", ())
-ERROR(throwing_call_in_nonexhaustive_catch,sema,none,
-      "call can throw, but the enclosing catch is not exhaustive", ())
 ERROR(throw_in_nonexhaustive_catch,sema,none,
       "error is not handled because the enclosing catch is not exhaustive", ())