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.
This patch also performs minor refactoring to align syntax parsing
context with the right scope. We start to support the generic clauses
because they are necessary pieces to construct struct or
function syntax node.
The default IndexingIterator for a custom collection is not suitable for
subclasses that specialize the element type the way libSyntax does.
Overriding it with a more specific iterator, even with something like
covariant overrides, would not work because it the iterator is generic
over its base collection, not its element type.
Provide a custom iterator parameterized by the element type instead.
* [SwiftSyntax] Fix SyntaxChildren iteration
SyntaxChildren.Iterator stops the first time it sees a nil child;
since it traverses all indexes without considering presence, this
causes it to terminate iteration early if there is a missing child
in the list.
* [SwiftSyntax] Add tests for SyntaxChildren
* Unify the capitalization across all user-visible error messages (fatal errors, assertion failures, precondition failures) produced by the runtime, standard library and the compiler.
* Update some more tests to the new expectations.
* Create Swift libSyntax API
This patch is an initial implementation of the Swift libSyntax API. It
aims to provide all features of the C++ API but exposed to Swift.
It currently resides in SwiftExperimental and will likely exist in a
molten state for a while.
* Only build SwiftSyntax on macOS
