gh-158540: Add the profiled script's directory to sys.path

[hetaozdh]

Fixes gh-158540.

When a script is executed with python -m profiling.sampling run script.py
from another directory, the script cannot import modules placed next to it:
_sync_coordinator._execute_script() runs it with the working directory
(added by _setup_environment() for the -m case) as sys.path[0]
instead of the script's own directory.

This change adds the script's directory to sys.path in _execute_script(),
matching the behavior of python script.py.

Added a regression test in
Lib/test/test_profiling/test_sampling_profiler/test_sync_coordinator.py
that runs the coordinator on a script importing a sibling module, plus a
Misc/NEWS.d entry.

Tests:

• ./python -m test test_profiling
• ./python Tools/patchcheck/patchcheck.py

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[maurycy]

What do you think about this edge case?

2026-10-01T12:57:30.615506000+0200 maurycy@gimel /Users/maurycy/work/cpython-pr158548 (pr158548 91c5ab3?) % tree w
w
├── link.py -> sub/where.py
└── sub
    ├── helper.py
    └── where.py

2 directories, 3 files
2026-10-01T12:57:32.453682000+0200 maurycy@gimel /Users/maurycy/work/cpython-pr158548 (pr158548 91c5ab3?) % sudo ./python.exe -m profiling.sampling run w/link.py
Traceback (most recent call last):
  File "<frozen runpy>", line 201, in _run_module_as_main
  File "<frozen runpy>", line 87, in _run_code
  File "/Users/maurycy/work/cpython-pr158548/Lib/profiling/sampling/_sync_coordinator.py", line 261, in <module>
    main()
    ~~~~^^
  File "/Users/maurycy/work/cpython-pr158548/Lib/profiling/sampling/_sync_coordinator.py", line 254, in main
    _execute_script(script_path, script_args, cwd)
    ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/maurycy/work/cpython-pr158548/Lib/profiling/sampling/_sync_coordinator.py", line 201, in _execute_script
    exec(code, main_module.__dict__)
    ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/maurycy/work/cpython-pr158548/w/link.py", line 1, in <module>
    import helper
ModuleNotFoundError: No module named 'helper'
2026-10-01T12:57:43.707720000+0200 maurycy@gimel /Users/maurycy/work/cpython-pr158548 (pr158548 91c5ab3?) % ./python.exe -VV
Python 3.16.0a0 (heads/pr158548:91c5ab3e096, Oct  1 2026, 10:22:50) [Clang 21.0.0 (clang-2100.3.34.2)]

I'm wondering if this might be an approach to mimic:

cpython/Lib/pdb.py

Lines 192 to 197 in 763b6ed

	self._target = self._safe_realpath(target)
	# If PYTHONSAFEPATH (-P) is not set, sys.path[0] is the directory
	# of pdb, and we should replace it with the directory of the script
	if not sys.flags.safe_path:
	sys.path[0] = os.path.dirname(self._target)

[hetaozdh]

Thanks for the comment. Fixed in 264a36c

[maurycy]

A note for the reviewer is that there are two approaches in the stdlib.

pdb does not insert but replace:

cpython/Lib/pdb.py

Line 197 in 763b6ed

sys.path[0] = os.path.dirname(self._target)

Same as trace:

cpython/Lib/trace.py

Line 730 in ab01d18

sys.path[0] = os.path.dirname(opts.progname)

While profile does insert:

cpython/Lib/profile.py

Line 600 in ab01d18

sys.path.insert(0, os.path.dirname(progname))