uv plugin fails on core26: dispatch script uses system Python instead of venv
Metadata
Current evaluation
uv plugin fails on core26: craft-parts removes python symlinks from venv/bin/, dispatch script falls back to system Python without venv packages. Triaged and moved to Charmcraft by maintainer.
Suggested action: keep open
Reason: The issue has been triaged (labeled Status: Triaged, Type: Bug) and a maintainer (@lengau) responded on 2026-07-15, explicitly moving it to Charmcraft directly. The bug is valid with clear reproduction steps and root cause analysis showing craft-parts removes python symlinks from venv/bin/ on core26, causing the dispatch script to fall back to system Python without venv packages.
Impact:
55
Quick Win:
24.75
Staleness:
45
Complexity:
55
Confidence:
75
Support Request:
15
Issue body
## Problem
The uv plugin fails when building charms on Ubuntu 26.04 (core26) because craft-parts removes python symlinks from `venv/bin/` and the dispatch script's fallback uses the system Python interpreter, which doesn't have venv packages installed.
## Root Cause
On core26, the base snap does NOT include Python. The uv plugin flow:
1. Creates a venv with `uv venv --relocatable --python /usr/bin/python3.14`
2. Runs `uv sync` to install dependencies (ops, cosl, etc.)
3. craft-parts removes `python*` symlinks from `venv/bin/`
4. craft-parts tries to find Python in the payload - fails (core26 has no Python)
5. craft-parts falls back to system interpreter path `/usr/bin/python3.14`
6. The dispatch script checks if `venv/bin/python` exists - it doesn't
7. The dispatch script creates `ln -s $(which python3) venv/bin/python`
8. This symlinks to the system Python, which doesn't have `ops` installed
Result: `ModuleNotFoundError: No module named 'ops'` at runtime.
## Reproduction
```yaml
base: ubuntu@26.04
parts:
charm:
plugin: uv
source: .
build-snaps:
- astral-uv
```
## Build Output
```
:: + uv venv --relocatable --allow-existing --python /usr/bin/python3.14 /root/parts/charm/install/venv
:: + uv sync --no-dev --no-editable --reinstall --no-install-project
:: + rm /root/parts/charm/install/venv/bin/python /root/parts/charm/install/venv/bin/python3 /root/parts/charm/install/venv/bin/python3.14
:: + echo 'Python interpreter not found in payload.'
:: Python interpreter not found in payload.
:: + symlink_target=/usr/bin/python3.14
```
The dispatch script then creates `venv/bin/python -> /usr/bin/python3`, which doesn't have venv packages.
## Runtime Error
```
File "/var/lib/juju/agents/unit-image-garden-stream-0/charm/src/charm.py", line 20, in <module>
from ops.charm import CharmBase
ModuleNotFoundError: No module named 'ops'
```
## Related
- craft-parts canonical/craft-parts#1580 - claims "core26+ and bare are fine" but this shows they are not
## Suggested Fix
Options:
1. On core26, automatically include python3 as a dependency in the payload
2. Don't remove python symlinks from venv/bin/ when the interpreter is not in the payload
3. Have craft-parts copy the interpreter to the payload when it's not available
4. Document that core26 requires additional configuration for the uv plugin
Evaluation history
| Date | Model | Scores | Action | Summary |
|---|---|---|---|---|
| qwen3.6-35b-a3b-mtp-q6 |
Impact:
55
Quick Win:
24.75
Staleness:
45
Complexity:
55
Confidence:
75
Support Request:
15
|
keep open | uv plugin fails on core26: craft-parts removes python symlinks from venv/bin/, dispatch script falls back to system Python without venv packages. Triaged and moved to Charmcraft by maintainer. | |
| qwen/qwen3.6-35b-a3b |
Staleness:
5
Complexity:
65
Confidence:
90
Support Request:
5
|
keep open | uv plugin fails on core26 because craft-parts removes venv Python symlinks, causing the dispatch script to fall back to system Python which lacks required packages. Issue is triaged and under investigation. | |
| qwen3.6-35b-a3b-mtp-q6 |
Staleness:
5
Complexity:
65
Confidence:
90
Support Request:
5
|
keep open | Bug report detailing uv plugin failure on Ubuntu core26 due to dispatch script falling back to system Python instead of using the venv. Acknowledged by maintainer and moved to Charmcraft for tracking. |
Update history
No update history recorded yet.
Related work
-
Related To:
craft-parts#1580
(confidence 80%)
Mentioned in issue body as claiming 'core26+ and bare are fine' but this issue demonstrates they are not. That issue was closed without resolution.
Related issues
| Issue | Project | State | Summary | Similarity |
|---|---|---|---|---|
| #1641 uv plugin fails on core26: dispatch script uses system Python instead of venv | craft-parts | open | uv plugin fails on core26: craft-parts removes python symlinks from venv/bin/ and dispatch script falls back to system Python without venv packages |