rebenitez1802 opened a new pull request, #42725:
URL: https://github.com/apache/superset/pull/42725
### SUMMARY
The MCP `generate_chart` / `update_chart` tools persisted the Handlebars
chart
template under the snake_case `form_data` key `handlebars_template`, but the
Handlebars viz renderer reads the camelCase key `handlebarsTemplate`
(`plugins/plugin-chart-handlebars/src/Handlebars.tsx`). As a result, a saved
chart's template never matched what the renderer read, so it fell back to the
default `{{data}}` output — the custom template never applied, and since only
the default template was present, its CSS had nothing to style either.
This mirrors the fix already in place one line below for the CSS, which is
correctly stored under the camelCase `styleTemplate`. The template key was
simply missed. The change persists the template under the camelCase key the
renderer reads:
```diff
- "handlebars_template": config.handlebars_template,
+ "handlebarsTemplate": config.handlebars_template,
```
- The persisted **output** key is the only thing that changes. The tool's
snake_case **request-contract** field
(`HandlebarsChartConfig.handlebars_template`),
its schema, validator, and LLM-facing examples are unchanged and remain
snake_case.
- One edit covers both `generate_chart` and `update_chart` — all persistence
funnels through `map_config_to_form_data`.
- No backend code reads the persisted key back for query building (Handlebars
renders client-side over rows), so blast radius is limited to making the
renderer's primary read succeed. It can only fix, never regress.
Paired write-side companion to #39442, which added a snake→camel read-side
fallback in the two controls' `mapStateToProps`. That fallback rescues the
Explore / direct-link render but not the dashboard-tile or in-chat-preview
paths (which hydrate via `applyDefaultFormData` and never run
`mapStateToProps`).
Persisting the correct key fixes every render path for newly created/updated
charts.
### BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
N/A — backend `form_data` key fix; no visual change beyond the custom
template
now rendering instead of the default `{{data}}` output.
### TESTING INSTRUCTIONS
- `pytest tests/unit_tests/mcp_service/chart/test_handlebars_chart.py`
(updated
`test_aggregate_mode_basic` asserts the camelCase key and the absence of
the
snake_case key).
- End-to-end: via the MCP `generate_chart` tool, create a Handlebars chart
with
a custom template + CSS and save it. Open the saved chart in Explore, via
direct link, and on a dashboard tile — the custom template + CSS render on
all
three and match the in-chat preview. Inspect the saved chart's `params` and
confirm it contains `"handlebarsTemplate"` (not `"handlebars_template"`).
### 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
Related: #39442 (read-side control fallback).
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