richardfogaca opened a new pull request, #40077:
URL: https://github.com/apache/superset/pull/40077
### SUMMARY
`update_chart_preview` already accepted `generate_preview` and
`preview_formats`, but after producing the updated explore URL it always
returned an empty `previews` object. That meant callers could get a table
preview from `generate_chart` and then lose the same requested preview when
updating the generated chart preview.
This change routes supported update-preview formats through the existing
unsaved form-data preview generator after the updated form data has been
mapped, access-checked, validated, and cached. URL previews remain represented
by the returned explore URL fields, so URL-only requests still succeed with
empty data previews.
The change is limited to the MCP update-preview response path and does not
alter saved chart persistence or `generate_chart` preview behavior.
Reviewer focus:
- `superset/mcp_service/chart/tool/update_chart_preview.py` now generates
only supported data preview formats: `ascii`, `table`, and `vega_lite`.
- `tests/unit_tests/mcp_service/chart/tool/test_update_chart_preview.py`
covers the requested table preview path and confirms URL is skipped as a
data-preview format.
### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
N/A - backend-only MCP chart tool response behavior.
Before this change, an update preview request with `generate_preview: true`
and `preview_formats: ["table"]` returned `previews: {}` even though the
initial chart generation returned a table preview for the same dataset/config
shape.
After this change, the update preview response returns the requested table
preview. Adjacent checks also verified that `ascii`, `table`, and `vega_lite`
are returned when requested, while URL-only requests continue to return the
explore URL with no data preview entries.
### TESTING INSTRUCTIONS
- [x] `docker compose -p superset-sc-104343-update-chart-preview-previews
exec -T superset pytest
tests/unit_tests/mcp_service/chart/tool/test_update_chart_preview.py`
- [x] `docker compose -p superset-sc-104343-update-chart-preview-previews
exec -T superset python -m ruff check
superset/mcp_service/chart/tool/update_chart_preview.py
tests/unit_tests/mcp_service/chart/tool/test_update_chart_preview.py`
- [x] Manual MCP/API verification: call `generate_chart` with
`generate_preview: true` and `preview_formats: ["table"]`, then call
`update_chart_preview` with the returned `form_data_key` and the same preview
parameters. Both responses include a table preview.
- [x] Manual MCP/API regression check: `update_chart_preview` returns
`ascii`, `table`, and `vega_lite` preview keys when all three are requested,
and URL-only preview requests still return success with an explore URL and an
empty `previews` object.
### ADDITIONAL INFORMATION
- [ ] Has associated issue:
- [ ] Required feature flags:
- [ ] Changes UI
- [ ] Includes DB Migration (follow approval process in
[SIP-59](https://github.com/apache/superset/issues/13351))
- [ ] Migration is atomic, supports rollback & is backwards-compatible
- [ ] Confirm DB migration upgrade and downgrade tested
- [ ] Runtime estimates and downtime expectations provided
- [ ] Introduces new feature or API
- [ ] Removes existing feature or API
<!-- agor:pr-summary:begin -->
### What Changed
The update preview API flow now builds data previews after the updated form
data has passed dataset access checks, form-data validation, and explore URL
cache generation. It reuses the existing unsaved form-data preview generator
for supported data-preview formats instead of adding a separate formatter in
the update path.
Only `ascii`, `table`, and `vega_lite` are passed into data-preview
generation. URL and screenshot-style preview requests continue to be
represented by the returned explore URL fields, so URL-only update requests
still return an empty `previews` object.
### Validation
The original bug shape was verified by generating a chart with
`generate_preview: true` and `preview_formats: ["table"]`, then updating it
with the returned `form_data_key` and the same preview options. After the fix,
both responses include a table preview.
Adjacent preview formats were checked by requesting `ascii`, `table`, and
`vega_lite` together from `update_chart_preview`, and URL-only preview requests
still succeed with an explore URL and no data-preview entries. The focused unit
test file for `update_chart_preview` passes with `22 passed`.
### Reviewer Focus
The main behavior contract is in
`superset/mcp_service/chart/tool/update_chart_preview.py`: preview generation
happens only after the updated unsaved chart state is validated and cached. The
corresponding tests in
`tests/unit_tests/mcp_service/chart/tool/test_update_chart_preview.py` cover
the supported table preview path and the URL-skip behavior.
### Risk / Rollback
Risk is limited to the MCP update-preview response path. The change does not
alter saved chart persistence, `generate_chart` preview behavior, or explore
URL generation. Rollback is reverting this PR.
<!-- agor:pr-summary:end -->
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