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Posted to notifications@superset.apache.org by "Nuno23C (via GitHub)" <gi...@apache.org> on 2026/05/22 08:52:16 UTC
[I] Partial override of THEME_DEFAULT in superset_config.py crashes the frontend with a white screen on 6.1.0 [superset]
Nuno23C opened a new issue, #40375:
URL: https://github.com/apache/superset/issues/40375
### Bug description
## How to reproduce the bug
1. Start from a stock Superset 6.1.0 deployment (e.g. `apache/superset:6.1.0`).
2. Add the following to `superset_config.py` — a minimal partial override of `THEME_DEFAULT`, matching the pattern shown in PR #35220's own testing instructions:
```python
THEME_DEFAULT = {
"token": {
"colorPrimary": "#ff0000",
},
"algorithm": "default",
}
```
3. Restart the web container.
4. Open `/login/` in a browser with DevTools → Console open.
### Expected results
The login page renders with the customized `colorPrimary`. Unspecified token fields fall back to the built-in defaults (consistent with what the official theming docs promise: *"Superset validates theme JSON… falls back to the built-in default theme rather than applying a broken configuration."*).
### Actual results
The page is blank. The console shows:
```
Failed to apply theme: TypeError: Cannot read properties of undefined (reading 'startsWith')
at n (vendors.<hash>.entry.js:8:21553)
at es (8085.<hash>.entry.js:8:735:950)
at ii (vendors.<hash>.entry.js:550:51407)
at iW (vendors.<hash>.entry.js:550:60874)
at c (vendors.<hash>.entry.js:554:22700)
...
```
The React app crashes during boot. Subsequent calls to `/api/v1/theme/?q=(filters:!((col:is_system_default,opr:eq,value:!t)))` return `401 Unauthorized` (unauthenticated, because the user is on the login page) but those are downstream of the crash, not its cause.
### Evidence
In a working pod, the partial-override config produces this `bootstrapData?.common?.theme` (queryable via `JSON.parse(document.querySelector('#app').dataset.bootstrap)` in the console):
```js
{
default: {
algorithm: "default",
token: {
colorPrimary: "#ff0000", // ← only the user-supplied field
} // ← ~22 expected fields missing
},
dark: {
algorithm: "dark",
token: {
brandAppName: "Apache Superset",
brandLogoHref: "/",
fontFamily: "Inter, Helvetica, Arial, sans-serif",
// ... 22 more fields, all populated from upstream defaults
}
}
}
```
The active `default.token` has **1 field** (the user override) and `dark.token` has the full upstream set. Dark mode renders correctly (with upstream blue colors, not the user override) because its token was constructed in `config.py` via `{**THEME_DEFAULT, "token": {**THEME_DEFAULT["token"], ...}, "algorithm": "dark"}` *before* the user override took effect, so the snapshot is complete.
### Environment
- Superset 6.1.0 (apache/superset:6.1.0 official image)
- Reproducible with any partial `THEME_DEFAULT` override in `superset_config.py`
- Not specific to any browser, OS, database, or deployment topology
---
## Regression analysis
On 6.0.0, `THEME_DEFAULT` in `superset/config.py` was effectively empty (`{"algorithm": "default"}`) and the same partial-override pattern worked. On 6.1.0, [PR #35220](https://github.com/apache/superset/pull/35220) populated `THEME_DEFAULT` with ~22 token fields and reframed it as the canonical base theme for the application. After that PR, a partial override no longer falls back gracefully — the React app crashes on boot because token fields it expects to be present are `undefined`. We have not pinpointed which specific frontend code path calls `.startsWith()` on which missing field.
---
## Suggested fix
A partial override of `THEME_DEFAULT` in `superset_config.py` should preserve unspecified token fields from the upstream default — matching what users reasonably expect from a "base theme" customization. Concretely: setting only `THEME_DEFAULT["token"]["colorPrimary"]` should still leave the other 21 upstream token fields in the effective theme that ships to the frontend.
---
## Workaround (for anyone who lands here via search)
Until this is fixed upstream, extend the default theme rather than replace it:
```python
from superset.config import THEME_DEFAULT as _UPSTREAM_THEME_DEFAULT
THEME_DEFAULT = {
**_UPSTREAM_THEME_DEFAULT,
"token": {
**_UPSTREAM_THEME_DEFAULT["token"],
# your overrides here:
"colorPrimary": "#ff0000",
},
}
```
This restores the full 22-field token while applying your customizations on top.
### Screenshots/recordings
_No response_
### Superset version
master / latest-dev
### Python version
3.9
### Node version
16
### Browser
Chrome
### Additional context
_No response_
### Checklist
- [ ] I have searched Superset docs and Slack and didn't find a solution to my problem.
- [x] I have searched the GitHub issue tracker and didn't find a similar bug report.
- [ ] I have checked Superset's logs for errors and if I found a relevant Python stacktrace, I included it here as text in the "additional context" section.
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Re: [I] Partial override of THEME_DEFAULT in superset_config.py crashes the frontend with a white screen on 6.1.0 [superset]
Posted by "rusackas (via GitHub)" <gi...@apache.org>.
rusackas commented on issue #40375:
URL: https://github.com/apache/superset/issues/40375#issuecomment-4594773608
Can you open the PR against Superset's `master` if you want others to benefit here?
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Re: [I] Partial override of THEME_DEFAULT in superset_config.py crashes the frontend with a white screen on 6.1.0 [superset]
Posted by "rusackas (via GitHub)" <gi...@apache.org>.
rusackas closed issue #40375: Partial override of THEME_DEFAULT in superset_config.py crashes the frontend with a white screen on 6.1.0
URL: https://github.com/apache/superset/issues/40375
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Re: [I] Partial override of THEME_DEFAULT in superset_config.py crashes the frontend with a white screen on 6.1.0 [superset]
Posted by "dosubot[bot] (via GitHub)" <gi...@apache.org>.
dosubot[bot] commented on issue #40375:
URL: https://github.com/apache/superset/issues/40375#issuecomment-4517210470
<!-- Greeting -->
Hi @Nuno23C! I'm [Dosu](https://go.dosu.dev/dosubot) and I’m helping the superset team.
<!-- Answer -->
This is a confirmed issue — another user reported the exact same `"Cannot read properties of undefined (reading 'startsWith')"` crash in [#39855](https://github.com/apache/superset/issues/39855) [[1]](https://github.com/apache/superset/issues/39855) when using partial theme configurations in `superset_config.py`.
Your root cause analysis is spot-on. The Python backend does a **simple dictionary replacement** — there is no deep-merge logic for theme config overrides [[2]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset/config.py). The frontend *does* have token-level merging in `Theme.setConfig()` via spread operator (`{...Theme.defaultTokens, ...(antdConfig.token || {})}`) [[3]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset-frontend/packages/superset-ui-core/src/theme/Theme.tsx#L154-L161), but by the time a partial token object reaches that code path, other parts of the app have already attempted to read missing properties and crashed.
Interestingly, the **UI-based theme editor** works correctly with partial overrides because it uses `_merge_theme_dicts()` — the recursive merge function introduced in PR #35220 for database-stored themes . That same merge logic was never applied to `superset_config.py` overrides, which is the inconsistency.
Your workaround (importing and spreading over `THEME_DEFAULT`) is the correct approach until a fix lands. The fix itself would be straightforward — apply the same `_merge_theme_dicts()` logic to config-file themes before passing them to bootstrap data [[4]](https://github.com/apache/superset/blob/829e4d92d91ceae4b43b1ed3b063ffe45377799c/superset/views/base.py#L374).
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