Instead of being a part of 'directDependencies' on a module dependency info, make them a separate array of dependency IDs for Swift Source and Textual modules.
This will allow clients to still distinguish direct module dependencies imported from a given module, versus dependencies added because direct/transitive Clang module dependencies have Swift overlays.
This change does *not* remove overlay dependencies from 'directDependencies' yet, just adds them as a separate field on the module details info. A followup change will remove overlay and bridging header dependencies from 'directDependencies' once the clients have had a chance to adopt to this change.
This matches the behavior of the current client (`swift-driver`) and reduces ambiguity in how the nodes in the graph are to be treated. Swift dependencies with a textual interface, for example, must be built into a binary module by clients. Swift dependencies without a textual interface, with only a binary module, are to be used directly, without any up-to-date checks.
Note, this is distinct from Swift dependencies that have a textual interface, for which we also detect potential pre-build binary module candidates. Those are still reported in the `details` field of textual Swift dependencies as `prebuiltModuleCandidates`.
In the fast dependency scanner, depending on whether a module intrface was found via the import search path or framework search path, encode into the dependency graph Swift module details, whether a given module is a framework.
Instead of replacing an interface file with its up-to-date compile module,
the dep-scanner should report potentially up-to-date module candidates either adjacent to
the interface file or in the prebuilt module cache. swift-driver should later pass down
these candidates to -compile-module-from-interface invocation and the front-end job
will check if one of the candidates is ready to use. The front-end job then either emits a forwarding
module to an up-to-date candidate or a binary module.
For the explicit module mode, swift-driver uses -compile-module-from-interface to
generate modules from interfaces found by the dependency scanner. However, we don't
need to build the binary module if up-to-date modules are available, either adjacent
to the interface file or in the prebuilt module cache directory. This patch teaches
dependencies scanner to report these ready-to-use binary modules.
Building each Swift module explicitly requires dependency PCMs to be built
with the exactly same deployment target version. This means we may need to
build a Clang module multiple times with different target triples.
This patch removes the -target arguments from the reported PCM build
arguments and inserts extraPcmArgs fields to each Swift module.
swift-driver can combine the generic PCM arguments with these extra arguments
to get the command suitable for building a PCM specifically for
that loading Swift module.
