We have two similar objects for source location. AbsoluteLocation
calculates the offset of a syntax node on the fly. SourceLocation is
designed to serialize a Swift syntax diagnostics to the driver. The only
difference is AbsoluteLocation doesn't contain source file name however
SourceLocation does. This patch bridges them by making AbsoluteLocation
a private member of SourceLocation. We also expect Swift syntax to
be file-name agnostic. The clients should keep track of the file name
when emitting diagnostics.
This patch provides an API and Serialization for clang-style diagnostics
from within Swift. Libraries can use this API to pop their own custom
diagnostics that can be serialized to JSON.
