yaml validation errors are not helpful if the file is empty

Metadata

Project: charmcraft
Number: #2071
Type: issue
State: open
Author: PietroPasotti
Labels: —
Created: 2025-01-10 12:51 PM UTC
Updated: 2025-08-15 03:18 PM UTC
Closed: —

Current evaluation

charmcraft pack gives a generic 'Invalid file: metadata.yaml' error when the file is empty (comments only), making it hard to diagnose. A maintainer acknowledged it in June 2025 and left it open as low priority; the error is still generic in current code.

Suggested action: keep open

Reason: Maintainer @lengau explicitly triaged this on 2025-06-13 ('I'm going to leave this open if anyone else wants to do it'), so it is acknowledged and valid, not stale-closable. I confirmed in charmcraft/preprocess.py that the empty-file case still hits the generic 'Invalid file: metadata.yaml' CraftValidationError, so the problem remains applicable. The fix is a small UX improvement (special-case empty/None YAML load), but low priority per the maintainer.

Impact: 25 Quick Win: 21.25 Staleness: 70 Complexity: 15 Confidence: 85 Support Request: 10

Issue body

### Bug Description validation error is not helpful on an empty file. (it was actually hard to find out that the file was empty because I thought I'd deleted it). The project already had a (valid) charmcraft.yaml next to it, and couldn't figure out why charmcraft wasn't liking it. ### To Reproduce charmcraft pack ### Environment charmcraft 3.2.2 ### metadata.yaml ```yaml # Copyright 2025 Canonical Ltd. # See LICENSE file for licensing details. ``` ### Relevant log output ```shell ❯ charmcraft pack Invalid file: 'metadata.yaml' Recommended resolution: Ensure metadata.yaml meets the juju metadata.yaml specification. For more information, check out: https://juju.is/docs/sdk/metadata-yaml Full execution log: '/home/pietro/.local/state/charmcraft/log/charmcraft-20250110-134846.839621.log' ```

Evaluation history

Date	Model	Scores	Action	Summary
2026-09-01 12:15 AM UTC	qwen/qwen3.8-27b	Impact: 25 Quick Win: 21.25 Staleness: 70 Complexity: 15 Confidence: 85 Support Request: 10	keep open	charmcraft pack gives a generic 'Invalid file: metadata.yaml' error when the file is empty (comments only), making it hard to diagnose. A maintainer acknowledged it in June 2025 and left it open as low priority; the error is still generic in current code.
2026-07-22 12:38 AM UTC	qwen/qwen3.6-35b-a3b	Staleness: 55 Complexity: 20 Confidence: 90 Support Request: 10	keep open	Empty YAML files produce unhelpful validation errors in charmcraft. Reported as a bug, acknowledged by a maintainer, but currently unassigned and waiting for community contribution.
2026-07-07 08:52 PM UTC	qwen3.6-35b-a3b-mtp-q6	Staleness: 80 Complexity: 20 Confidence: 85 Support Request: 10	keep open	Unhelpful validation error when metadata.yaml is empty. Acknowledged by maintainers but marked low priority with no engineering time allocated.
2026-07-05 02:42 AM UTC	qwen3.6-35b-a3b-mtp-q6	Staleness: 75 Complexity: 15 Confidence: 85 Support Request: 10	keep open	Unhelpful validation error for empty YAML files. Maintainer acknowledged and left open as low priority.
2026-06-15 10:14 PM UTC	qwen3.6-35b-a3b-mtp-q6	Staleness: 65 Complexity: 15 Confidence: 95 Support Request: 0	keep open	charmcraft pack shows unhelpful validation errors for empty YAML files. The issue is open and available for community contribution, with no immediate engineering plans to fix it.

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