No way to pass "-undefined dynamic_lookup" to Darwin linker for Zig sources?

[haberman]

To build a native Python extension on Darwin, the option -undefined dynamic_lookup must be passed to the linker to indicate that unresolved symbols will be resolved at runtime.

More info here: Please use -undefined dynamic_lookup instead of -lpython or -framework Python to build Python extension modules on OS X

Otherwise you get errors like this:

cmd zig build-lib -dynamic -DPYHEXVER=50857456 --name pdfxt.cpython-38-darwin -I /Users/haberman/opt/anaconda3/include/python3.8 -I /usr/include pdfxt.zig
warning(link): unexpected LLD stderr:
Undefined symbol: zig-cache/o/90680a79ab7f51bd67f93a83b363da55/pdfxt.cpython-38-darwin.o: __PyArg_ParseTuple_SizeT
Undefined symbol: zig-cache/o/90680a79ab7f51bd67f93a83b363da55/pdfxt.cpython-38-darwin.o: _PyLong_FromLong
Undefined symbol: zig-cache/o/90680a79ab7f51bd67f93a83b363da55/pdfxt.cpython-38-darwin.o: _PyModule_Create2
symbol(s) not found

For zig cc it appears there is an option --allow-shlib-undefined that will achieve the desired effect.

zig/src/main.zig

Lines 1260 to 1263 in 9270aae

	} else if (mem.eql(u8, arg, "--allow-shlib-undefined") or
	mem.eql(u8, arg, "-allow-shlib-undefined"))
	{
	linker_allow_shlib_undefined = true;

zig/src/link/MachO.zig

Lines 781 to 784 in 9270aae

	if (allow_shlib_undefined) {
	try argv.append("-undefined");
	try argv.append("dynamic_lookup");
	}

But I don't see any comparable option for build-lib.

I believe this is a blocker for writing native extensions on Darwin.

(Darwin also differentiates between "dynamic library" and "bundle," but the functional differences between these two have greatly lessened over time, so it's unclear if the ability to compile with -bundle is actually an important use case or not.)

[haberman]

Are you open to accepting a change that adds a link option for this?

[haberman]

As a workaround I tried using zig build-obj to turn .zig files into .o so I could link with the regular C compiler and pass -undefined dynamic_lookup that way:

$ zig build-obj -fPIC -DPYHEXVER=50857456 -I /Users/haberman/opt/anaconda3/include/python3.8 -I /usr/include pdf.zig
$ zig build-obj -fPIC -DPYHEXVER=50857456 -I /Users/haberman/opt/anaconda3/include/python3.8 -I /usr/include pdfxt.zig
$ gcc -dynamic -undefined dynamic_lookup pdfxt.o pdf.o -o pdfxt.so

I was able to build my .so this way, but it fails to load due to missing some stuff from compiler_rt:

Traceback (most recent call last):
  File "test.py", line 2, in <module>
    import pdfxt
ImportError: dlopen(/tmp/pdfxt.so, 2): Symbol not found: ___zig_probe_stack
  Referenced from: /tmp/pdfxt.so
  Expected in: flat namespace
 in /tmp/pdfxt.so

I tried passing -fcompiler-rt to zig build-obj but that doesn't appear to support Mach-O:

zig build-obj -fcompiler-rt -fPIC -DPYHEXVER=50857456 -I /Users/haberman/opt/anaconda3/include/python3.8 -I /usr/include pdfxt.zig
error: Embedding compiler-rt into macho objects is not yet implemented.

[andrewrk]

Thank you for detailing this use case. Closing in favor of #3085. I have modified the milestone of #3085 to be 0.8.0, indicating a plan to address the issue before the next release.