Fix GraalPy compatibility

[steve-s]

Fixes debugpy compatibility with GraalPy, an alternative Python implementation.

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[rchiodo]

GitHub cannot anchor PR review comments to unchanged lines in the diff. Falling back to a general PR comment for src/debugpy/server/api.py:L233.

📍 src/debugpy/server/api.py:222
GraalPy falls through both branches here: _CAN_DAEMONIZE is False yet os.name == "posix" is True, so neither if nor elif os.name != "posix" executes. Because the __main__.py change means the GraalPy adapter no longer double-forks, it is a long-lived direct child just like the Windows case and needs the same treatment. As written, GraalPy will miss returncode = 0 and re-emit the bpo-38890 "child still alive" warning. Fix: key the second branch on child lifetime, not OS name — use a plain else: (i.e. not _CAN_DAEMONIZE, covering Windows AND GraalPy) that sets returncode = 0.

[rchiodo]

📍 src/debugpy/launcher/debuggee.py:62
The process_group keyword for subprocess.Popen was only added in Python 3.11. A GraalPy build targeting a pre-3.11 stdlib (e.g. GraalPy 23.x → 3.10) will raise TypeError: got an unexpected keyword argument 'process_group', which is caught and surfaced as "Couldn't spawn debuggee" — making launch fail entirely rather than degrading. Guard it, e.g. if ... graalpy and sys.version_info >= (3, 11): kwargs.update(process_group=0), or wrap in try/except TypeError.

[steve-s]

This would also require adding another branch to kill so that we use os.kill and not os.killpg for older GraalPy versions. Moreover, support for current and older GraalPy releases depends on fabioz/PyDev.Debugger#325, and unless that's merged and propagated to debugpy I think it's better to keep the changes in this file simple - it will work on GraalPy master (and some future release) for which fixes in fabioz/PyDev.Debugger#325 aren't necessary.

[rchiodo]

Solid GraalPy compatibility work overall. The main blocker is the if _CAN_DAEMONIZE / elif os.name != "posix" structure in api.py, which silently drops GraalPy through both branches. Keying the second branch on child lifetime (else:) rather than OS name fixes it.

[steve-s]

Thank you for the review! I addressed the blocker in the last commit. I will have to figure out CLA with my company.

[rchiodo]

Small, well-scoped GraalPy compatibility fix. Note: the api.py daemonize change correctly routes GraalPy into the plain else branch (same path as Windows), so it still receives returncode = 0 and the don't-terminate registration — no missed-warning regression. Looks good to merge.

[rchiodo]

Approved via Review Center.

[rchiodo]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[rchiodo]

The extra variable outside of the if statement seems like overkill. Why not just have this:

if hasattr(os, "fork") and os.fork() != 0:

[rchiodo]

Same thing here. It would be

if os.name == "posix" and hasattr(os, "fork")

Makes for fewer code changes.

[rchiodo]

📍 src/debugpy/adapter/main.py:38
This PR adds a hasattr(os, "fork") probe but leaves the sibling syscalls os.getsid/os.setsid (a few lines up in the same if os.name == "posix": block) gated only on os.name == "posix". A forkless-POSIX runtime that also lacks setsid would raise AttributeError/OSError here and crash before reaching the new fork guard — defeating the PR's goal. Please confirm GraalPy exposes setsid/getsid, or guard with hasattr(os, "setsid") / wrap in try/except (AttributeError, OSError).

[steve-s]

yes, GraalPy exposes those functions

[rchiodo]

Approved via Review Center.

[rchiodo]

Approved via Review Center.

[rchiodo]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[heejaechang]

GitHub cannot anchor PR review comments to unchanged lines in the diff. Falling back to a general PR comment for src/debugpy/launcher/debuggee.py:L36.

📍 src/debugpy/launcher/debuggee.py:33

This file detects the fork-less runtime by identity (sys.implementation.name == "graalpy"), while adapter/__main__.py and server/api.py detect it by capability (hasattr(os, "fork")). They encode the same concept two ways, so a future fork-less POSIX runtime would be routed correctly by the other two files but fall into the != 'graalpy' branch here and attempt os.setpgrp() between fork and exec — exactly what the comment says is impossible. Consider unifying all three sites behind one shared predicate (e.g. a supports_fork() helper).

[heejaechang]

GitHub cannot anchor PR review comments to unchanged lines in the diff. Falling back to a general PR comment for src/debugpy/launcher/debuggee.py:L36.

📍 src/debugpy/launcher/debuggee.py:31

The original preexec_fn does two things: os.setpgrp() (own process group, required so the launcher's os.killpg(process.pid, ...) targets the whole tree) and tcsetpgrp(...) (make that group the terminal foreground). process_group=0 faithfully replaces only the first — the kill-tree invariant is preserved, but the foreground-terminal handling is silently dropped for GraalPy. Interactive terminal I/O on a real TTY may differ. At minimum, expand the comment to state the foreground-group behavior is intentionally not replicated and why.

[heejaechang]

GitHub cannot anchor PR review comments to unchanged lines in the diff. Falling back to a general PR comment for src/debugpy/launcher/debuggee.py:L36.

📍 src/debugpy/launcher/debuggee.py:33

process_group=0 is a Popen keyword added in CPython 3.11. On a GraalPy release whose stdlib tracks 3.8/3.10, Popen(..., process_group=0) raises TypeError: unexpected keyword argument, which would make launching any debuggee impossible — the opposite of this PR's goal. Consider feature-detecting ("process_group" in inspect.signature(subprocess.Popen).parameters) with a fallback, or documenting the minimum supported GraalPy version.

[heejaechang]

GitHub cannot anchor PR review comments to unchanged lines in the diff. Falling back to a general PR comment for src/debugpy/server/api.py:L55.

📍 src/debugpy/server/api.py:49

This hasattr(os, "fork") is evaluated in the server interpreter, but the process that actually decides to fork/daemonize is the adapter (spawned separately, with a potentially user-configured python). In a CPython-server + GraalPy-adapter combination the server sees fork, calls _adapter_process.wait(), but the adapter never forks/exits, so listen() can hang. Consider basing this decision on whether the adapter will daemonize rather than on the server's own os.fork.

[heejaechang]

Looks good overall and the approach is reasonable. The main theme of the feedback: the fork-less runtime is detected two different ways (sys.implementation.name == 'graalpy' vs hasattr(os, 'fork')) — worth unifying behind one predicate — and please confirm process_group=0 is available on your minimum supported GraalPy (it's a CPython 3.11+ Popen kwarg) and that dropping the tcsetpgrp foreground handling is acceptable.

[heejaechang]

Approved via Review Center.