*Their* dependencies are already being serialized out, so this shouldn't affect
up-to-date-checking except by alowing the regular and prebuilt module caches to
be relocated without invalidating their contents. In the case of the prebuilt
module cache, this gets us closer to supporting relocation across machines.
Updates the subinvocation that builds the parseable interface to respect the
-track-system-dependencies flag of the top-level invocation if present, by
including system dependencies in the produced .swiftmodule.
In addition to being wasteful, this is a correctness issue -- the
compiler should only ever have one view of this file, and it should not
read a potentially different file after validating dependencies.
rdar://48654608
...and remove the option. This is ~technically~ CLI-breaking because
Swift 5 shipped this as a hidden driver option, but it wouldn't have
/done/ anything in Swift 5, so I think it's okay to remove.
Note that if a parseable interface (.swiftinterface) and a binary
interface (.swiftmodule) are both present, the binary one will still
be preferred. This just /allows/ parseable interfaces to be used.
rdar://problem/36885834
A ‘forwarding module’ is a YAML file that’s meant to stand in for a .swiftmodule file and provide an up-to-date description of its dependencies, always using modification times.
When a ‘prebuilt module’ is first loaded, we verify that it’s up-to-date by hashing all of its dependencies. Since this is orders of magnitude slower than reading mtimes, we’ll install a `forwarding module` containing the mtimes of the now-validated dependencies.
