[swift-users] Annotating C APIs without changing the original header files

[Douglas Gregor]

> On May 3, 2017, at 4:10 PM, Geordie J via swift-users <swift-users at swift.org> wrote:
> 
> Hi everyone,
> 
> I’m about to start on another big project with Swift on Android and would like to annotate that JNI headers as much as possible before I do: specifically I’d like to make _Nonnull and CF_SWIFT_NAME annotations to the headers found in a user's jni.h.
> 
> The question is: is it possible to annotate headers this without changing the original header files? Specifically I’m looking for an options that allows annotations in a separate file, probably one that is read when loading the package’s module.modulemap.
> 
> I’d like to distribute the annotations in a SwiftPM package that also exposes the original (hopefully annotated) headers. Up until now I’ve been using Swift to override methods in code, but this isn’t as clean or extensible and I fear it may have other (particularly performance) implications.
> 
> I guess the alternative would be to just maintain and distribute a modified version of jni.h with the annotations, but that would be a "last resort” option.


This is the role of API notes, which you can see here:

	https://github.com/apple/swift/tree/master/apinotes <https://github.com/apple/swift/tree/master/apinotes>

with some rough documentation-in-source here:

	https://github.com/apple/swift-clang/blob/stable/lib/APINotes/APINotesYAMLCompiler.cpp

	- Doug

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