[thuanquang]

What

import_audit and stubgen error on Python 3.9 before reaching their assertions:

AttributeError: 'PosixPath' object has no attribute 'hardlink_to'

Path.hardlink_to was added in Python 3.10. Python 3.9.6 is the python3 that the Xcode command-line tools install on macOS, which is the toolchain BUILD.md names for the relinker-only build there, and tools/progress.py targets Python 3.9+ (#11). The two tests now create the hard link with os.link(target, link), which does the same on every Python 3 version and on Windows. Only the two test files change.

pr_overlap_encoding also fails on Python 3.9 (subprocess._text_encoding). That is a different cause, and #4361 changes that file, so it is left out here.

Overlap: #4425 also adds import os at the same place in tools/tests/test_import_audit.py. As agreed on #4425, it goes first; I will then rebase this one, keeping a single import os.

Tested

macOS 27 (Apple Silicon), AppleClang 21, relinker-only build of main (d592d54) with -DBUILD_TESTING=ON:

• Python 3.9.6 (Xcode command-line tools), before: import_audit and stubgen fail with the error above; 121/124 pass.
• Python 3.9.6, after: import_audit and stubgen pass; 123/124 pass, with pr_overlap_encoding the only failure.
• Python 3.11.4: test_import_audit.py (37 tests) and test_stubgen.py (11 tests) pass.
• python3 tools/check_conventions.py --base origin/main passes.

Not tested on Linux or Windows.

Checklist

• Based on current main; no other open PR implements the same functions
• One topic per PR; follow-ups go in a new PR
• No comments in code except technical debt
• Unimplemented paths throw (NotImplemented_nid_no_patch); silent stubs are listed in TechnicalDebt
• No notes, investigation .md files or images added to the repository (attach them to this PR)
• New third-party code is a submodule built from source
• Generic behaviour, not specific to one title
• Depends on: fix(import-audit): preserve JSON reports when writing fails #4425
• Unblocks: none
• AI-assisted: yes (Claude Code)

🤖 Generated with Claude Code

[coltken95]

Tested with Python 3.9.25, with 4feeef6 applied onto main 5d50886:

• On main: test_import_audit and test_stubgen error with
  AttributeError: 'PosixPath' object has no attribute 'hardlink_to'
• With the PR: all 48 tests in those two files pass.

For reference, tools/tests as a whole (252 tests) still has one failure on 3.9 that this PR doesn't touch:
test_pr_overlap_encoding.EncodingTests.test_default_encoding_uses_simulated_cp1252.
It passes on 3.11 and 3.13.

[xXPBSXx]

Windows test: head 4feeef698 merged onto current main 0f2683cb7, together with 5 other open pull requests in one build (the merges were conflict-free); a failure would have been bisected per PR. Windows 10, MinGW GCC (WinLibs), Ninja Release, -j2: full build 0 errors; ctest for the tests this change adds or touches: import_audit passed, stubgen passed; python tools/check_conventions.py --base upstream/main passed for the combined tree. I did not run the new tests against main without the change.

AI-assisted (Claude Code).

[adriadam10]

Checked: os.link(target, link) is equivalent to hardlink_to on every Python 3 version; test_stubgen.py already imports os. Merged on current main, scoped build and ctest pass (29/29). Python 3.9 results confirmed by @coltken95 (Linux 3.9.25) and Windows by @xXPBSXx; merging.