This is an experiment to create language bindings to macOS Objective-C APIs by parsing the output of 'clang -ast-dump=json'.
To dampen the expectations a bit: it's useful for replacing specific snippets of Objective-C code, but it's probably too brittle as a general solution for writing large macOS applications in 'random' programming languages. Reason being that the output of 'clang -ast-dump' exposes tons of small type definition details which need to be handled specifically by the output parser. Supporting new system header declarations is mostly a trial-and-error process where the parser balks at some of the more complex type definitions in the macOS system headers, so adding new declarations to be 'exported' is a trial-and-error process.
Conversion happens in two steps: first a simplified 'intermediate representation'
of the detailed AST output is generated with the script gen_ir.py.
gen_ir.py takes a JSON file as input which describes the declarations that
should be extracted from the system headers (C structs, enums and functions,
ObjC interfaces, protocols and categories and their methods).
The output of gen_ir.py is another JSON file with a simplified descriptions
of the extracted declarations:
> python3 gen_ir.py hello.json hello_ir.json
Running gen_ir.py takes a little while (10..20 seconds) because it
needs to chew through a several hundred megabytes big JSON file (the output
of clang -ast-dump), and there's also a couple of quadratic loops which
should be optimized.
The generated IR JSON file is then fed to a language-specific code-generation script. For instance to generate a C header:
> python gen_c.py hello_ir.json test/hello.h
The test subdirectory contains example programs which implement a
Cocoa+Metal Hello Triangle. hello.m is the 'reference' ObjC
implementation, hello.c is the C version which uses the generated
header hello.h.
To build the tests, run:
# build the ObjC reference:
> ./build_objc.sh
# build the C test:
> ./build_c.sh
This results in the executables hello_objc and hello_c.