Print implementation-only imports in the private textual interface
only if also importing SPI. This allows to export types from
implementation-only imports in SPI and brings the private textual
interfaces in line with the binary interfaces.
This is a temporary solution as we need to better design the language
feature around this.
This feature requires passing -experimental-spi-imports to the frontend
that generates the private swiftinterface file.
We have landed support for serialization Clang function types, but there is
still work to be done here.
Moreover, we should use a consistent style with `[(FIXME|TODO|NOTE): label]`,
instead of using different styles throughout the code.
Currently, when a swiftinterface file fails to load, we emit the specific diagnostics for the failures, followed by a generic “failed to load module ‘Foo’” message. This PR improves that final diagnostic, particularly when the cause may be that the interface was emitted by a newer compiler using backwards-incompatible syntax.
This reverts commit e805fe486e, which reverted
the change earlier. The problem was caused due to a simultaneous change to some
code by the PR with parsing and printing for Clang function types (#28737)
and the PR which introduced Located<T> (#28643).
This commit also includes a small change to make sure the intersecting region
is fixed: the change is limited to using the fields of Located<T> in the
`tryParseClangType` lambda.
