Fix running= with an ALL wildcard crashing when no components match

[Mohit-Ak]

Callbacks that use a pattern-matching id in running= crash the renderer as soon as you're on a page where none of those components exist. From #3297:

@callback(
    Output('data', 'data'),
    Input('reload-data', 'n_clicks'),
    running=[(Output({'type': 'loading', 'id': ALL}, 'display'), 'show', 'hide')],
)

Click the button while you're on the home page and it works. Navigate to /blank, which renders none of the {'type': 'loading', ...} components, click again, and the browser console throws state.paths.objs[idKey] is undefined. The callback never gets to run.

What was going wrong

getAllPMCIds indexes state.paths.objs[idKey] and calls .map on the result. paths.objs only has a key for an id shape that is actually rendered somewhere, so on a page with none of those components the lookup returns undefined and .map throws. The two other places that do this same lookup — resolveDeps in dependencies_ts.ts and getPath in paths.js — both guard it and return an empty result, so this was the odd one out. Guarding it the same way is the direct fix.

That turned out not to be the whole story though. replacePMC decides whether a wildcard was expanded by checking extras.length:

if (extras.length) {
    return extras;
}
return [replaced];

An ALL that legitimately matches zero components expands to an empty list, which is falsy, so control falls through to return [replaced] — and replaced only ever received the non-wildcard keys, because the wildcard branch writes to extras instead. So once the crash is gone you get [{type: 'loading'}] back: an id with the id key missing entirely. sideUpdate then treats that as a real component id and tries to update it. So I tracked expansion with an explicit flag rather than inferring it from the length, and made sideUpdate drop pattern-matching outputs that resolve to nothing, since in that case componentId still holds the unresolved pattern and isn't safe to use.

The "matches nothing" case is the correct outcome here, not an error — there is simply nothing to show or hide, and the callback should proceed normally. That's also why this doesn't route through the existing "ID running component not found in layout" error: that one is for a concrete id that isn't in the layout, whereas a wildcard matching zero components is expected behaviour when you're on a different page.

Testing

Added dash/dash-renderer/tests/patternMatching.test.js, which had no unit coverage before. It covers MATCH, ALL, plain concrete ids, and the two empty-page cases.

Before the source change, with the tests in place:

getAllPMCIds returns an empty list when no component uses that id shape FAILED
	TypeError: Cannot read properties of undefined (reading 'map')
	    at getAllPMCIds (build/commons.js:3121:34)
replacePMC yields no ids when ALL matches nothing on the current page FAILED
	TypeError: Cannot read properties of undefined (reading 'map')
replacePMC yields no ids when ALLSMALLER matches nothing on the current page FAILED
	TypeError: Cannot read properties of undefined (reading 'map')
TOTAL: 3 FAILED, 40 SUCCESS

That's the same error as the reported one, and the MATCH/ALL/concrete-id cases passed throughout, which is what confines the bug to the empty-match path.

After:

$ npm test
TOTAL: 43 SUCCESS

Lint is clean on the touched files (eslint 0 errors, prettier --list-different empty). tsc --noEmit reports the same set of pre-existing node_modules type errors before and after — none from these files.

Fixes #3297

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[camdecoster]

Thanks for the PR! Our team will take a look and provide some feedback.

[T4rk1n]

Fix is right, but the fix isn't fully tested yet. The diagnosis is accurate: getAllPMCIds was the one caller of state.paths.objs[idKey] that didn't guard the lookup (resolveDeps and getPath both do), and the extras.length overload in replacePMC did fall through to a partial id on a zero match. The explicit expanded flag is the correct split between "a wildcard expanded" and "the expansion was empty," and all the side-update kinds (running, runningOff, progress, set_props) go through the same guard, so the empty match is handled symmetrically.

The gap is coverage. This is two changes and only one is tested. The new unit tests exercise getAllPMCIds/replacePMC, but the callbacks.ts guard, the half that actually stops the unresolved pattern from reaching updateComponent, has no test at all, and nothing here reproduces #3297 end to end. The reported failure is a navigate-then-click crash in a running app; the PR proves the helpers in isolation but never proves the crash is gone. Please add a renderer integration test next to test_cbwc008_running_match: a two-page app, navigate to a page that renders none of the wildcard components, click the button, then assert the browser console is clean and the callback's own output still updates. That fails before this change and passes after, and it covers the callbacks.ts early return, not just the helpers.

Also tighten the CHANGELOG entry to two lines (house style, detail goes in .ai/): the crash plus the fix, drop the parenthetical.

[T4rk1n]

This early return is the half of the fix that keeps the unresolved pattern ({type: 'loading'} with no id) out of updateComponent, and it has no test. The unit tests stop at replacePMC returning [] and never reach this branch. Add an integration test modeled on test_cbwc008_running_match that reproduces #3297 directly: multi-page app, navigate to a page with none of the ALL components, click, then assert the console is clean and the callback output updated. That exercises this line and proves the actual crash is gone.

[T4rk1n]

Trim to two lines. Something like: "Fix running= with a pattern-matching ALL/ALLSMALLER id crashing the renderer when none of the matching components are on the current page. Fixes #3297." The navigation example and the resolve-to-empty detail belong in the commit body or .ai/.