pantsbuild / pants / 28578038934

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Pass the same set of object files when retrying linking for cgo (#23447)

With the latest `main` branch, `pants test
src/python/pants/backend/go/util_rules/cgo_test.py:tests` fails in my
environment:

```
============================= test session starts ==============================
collecting ... collected 5 items

src/python/pants/backend/go/util_rules/cgo_test.py::test_cgo_compile PASSED [ 20%]
src/python/pants/backend/go/util_rules/cgo_test.py::test_cgo_with_cxx_source FAILED [ 40%]
src/python/pants/backend/go/util_rules/cgo_test.py::test_cgo_with_objc_source FAILED [ 60%]
src/python/pants/backend/go/util_rules/cgo_test.py::test_cgo_with_fortran_source FAILED [ 80%]
src/python/pants/backend/go/util_rules/cgo_test.py::test_cgo_with_embedded_static_library PASSED [100%]

=================================== FAILURES ===================================
```

The 3 tests fail with the same linker error:

```
ValueError: cgo binary link failed:
stdout:

stderr:
Undefined symbols for architecture arm64:
  "_main", referenced from:
      <initial-undefines>
ld: symbol(s) not found for architecture arm64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

(found this issue during playing around the tests in
https://github.com/pantsbuild/pants/pull/23439)

In `cgo.py`, linking of object files are retried with additional linker
options:

https://github.com/pantsbuild/pants/blob/main/src/python/pants/backend/go/util_rules/cgo.py#L500-L559
For relatively simple case, linking succeeds at the 1st try. In the case
of ObjC, C++ and Fortran tests, linking fails (due to lack of the
language's stdlib?) and retried. `_main` (cgo-generated dummy function)
resides in `_cgo_main.o` file and is required by the linker, but the
object file is not included in the linker flags at the 2nd try.

My environment:
- OS: macOS 15.7.7
- gcc: clang-1700.6.4.2
- python: 3.14.6
- go: 1.26.2

1 of 1 new or added line in 1 file covered. (100.0%)

93775 of 101021 relevant lines covered (92.83%)

3.7 hits per line