[cards] debugging statements.

[valayDave]

PR Type

• Debugging
• Bug fix
• New feature
• Core Runtime change (higher bar -- see CONTRIBUTING.md)
• Docs / tooling
• Refactoring

Summary

Have a env var that allow debugging cards through metaflow's debug module.

[greptile-apps]

Greptile Summary

This PR adds a "card" debug option to Metaflow's debug module, enabling card-subsystem tracing via METAFLOW_DEBUG_CARD=1. Debug log calls are added at key lifecycle points in card creation and decoration.

• metaflow_config.py: registers \"card\" in DEBUG_OPTIONS, auto-generating debug.card_exec and the debug.card boolean flag.
• card_creator.py: adds logging around card creation, async process management, and subprocess error output; two minor issues in the exception handlers (dead-code conditional and unguarded UTF-8 decode).
• card_decorator.py: adds logging in task_pre_step and task_finished; changes are clean and well-placed.

Confidence Score: 4/5

Safe to merge; changes are limited to debug logging paths that only activate when METAFLOW_DEBUG_CARD is set.

All changes are confined to debug logging paths that only activate when METAFLOW_DEBUG_CARD is set, so normal card execution is unaffected. The dead-code ternary and unguarded UTF-8 decode in the exception handlers are worth cleaning up but cannot impact production runs.

metaflow/plugins/cards/card_creator.py — the exception handler debug blocks have a dead-code conditional and an unguarded UTF-8 decode worth cleaning up.

Important Files Changed

Filename	Overview
metaflow/metaflow_config.py	Adds "card" to DEBUG_OPTIONS, which causes the debug module to auto-generate debug.card_exec and debug.card attributes; straightforward and consistent with existing entries.
metaflow/plugins/cards/card_creator.py	Adds card-debug logging at key points in card creation; the exception handlers contain a dead-code ternary and a potential UnicodeDecodeError from bare rep.decode("utf-8"); the first debug statement also misses the early-return silent-ignore path.
metaflow/plugins/cards/card_decorator.py	Adds two debug log calls in task_pre_step and task_finished; clean and correctly placed after the relevant state is set.

_{Reviews (1): Last reviewed commit: "[cards] debugging statements." | Re-trigger Greptile}

[greptile-apps]

The "FAILED" if fail else "succeeded" conditional is dead code in both exception handlers — fail is set to True on the line immediately above, so the else branch can never execute. The suggestion also adds errors="replace" to rep.decode("utf-8") to avoid a UnicodeDecodeError if subprocess output contains non-UTF-8 bytes.

Suggested change

	except subprocess.CalledProcessError as e:
	rep = e.output
	fail = True
	if debug.card and rep is not None:
	debug.card_exec(
	"render subprocess for %s %s output:\n%s"
	% (
	card_uuid,
	"FAILED" if fail else "succeeded",
	rep.decode("utf-8"),
	)
	)
	except subprocess.TimeoutExpired as e:
	rep = e.output
	fail = True
	if debug.card and rep is not None:
	debug.card_exec(
	"render subprocess for %s %s output:\n%s"
	% (
	card_uuid,
	"FAILED" if fail else "succeeded",
	rep.decode("utf-8"),
	)
	)
	except subprocess.CalledProcessError as e:
	rep = e.output
	fail = True
	if debug.card and rep is not None:
	debug.card_exec(
	"render subprocess for %s FAILED output:\n%s"
	% (
	card_uuid,
	rep.decode("utf-8", errors="replace"),
	)
	)
	except subprocess.TimeoutExpired as e:
	rep = e.output
	fail = True
	if debug.card and rep is not None:
	debug.card_exec(
	"render subprocess for %s TIMED OUT output:\n%s"
	% (
	card_uuid,
	rep.decode("utf-8", errors="replace"),
	)
	)

[greptile-apps]

Silent-ignore case not captured by debug log

When mode != "render" and not runtime_card the method returns early (line 82) before reaching this debug.card_exec call, so calls that are silently dropped are invisible even with debug enabled. Moving the debug statement before the if/elif/else block (or adding a separate log in the early-return branch) would make this case observable.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[codecov]

Codecov Report

❌ Patch coverage is 25.00000% with 9 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@38797e3). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
metaflow/plugins/cards/card_creator.py	22.22%	7 Missing ⚠️
metaflow/plugins/cards/card_decorator.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #3273   +/-   ##
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  Coverage          ?   28.94%           
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  Files             ?      381           
  Lines             ?    52525           
  Branches          ?     9268           
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  Hits              ?    15202           
  Misses            ?    36287           
  Partials          ?     1036           

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