[Lens] bsearch not aborted after changing the layers

[afharo]

Kibana version: 8.0.0-rc1

Original install method (e.g. download page, yum, from source, etc.): Cloud deployment

Describe the bug:
After adding a field to break-down by in Lens, the main viz finished loading, but one of the suggestions in the graph kept loading. I changed my mind and changed/removed the break-down by field. The previously cached viz loaded instantly (including the suggestions). However, there's still the bsearch polling happening (and the load indicator on the top-left corner keeps spinning).

IMO, the polling should stop if that viz has changed.

Steps to reproduce:

1. Open Lens
2. Create any viz, breaking by a field. Try to make the query a long-running one to make it easier to test.
3. While the suggestions are loading, remove the break-by.
4. Notice that the bsearch request keeps polling because the previous query never finished.

Expected behavior:
IMO, the polling should stop if that viz has changed.

Screenshots (if relevant):

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:

[elasticmachine]

Pinging @elastic/kibana-vis-editors @elastic/kibana-vis-editors-external (Team:VisEditors)

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServicesSv)

[flash1293]

That's a great catch. It took me a bit to trace it to the root source, but it seems to be a general issue with how partial results and expression executions work.

The loader will cancel an ongoing expression if the execution will return isPending === true:

kibana/src/plugins/expressions/public/loader.ts

Line 133 in 73a0fc0

if (this.execution && this.execution.isPending) {

It will return false if the state of the execution is result:

kibana/src/plugins/expressions/common/execution/execution_contract.ts

Line 23 in 92a8636

const finished = state === 'error' || state === 'result';

However the state is set to result as soon as the setResult transition is triggered:

kibana/src/plugins/expressions/common/execution/container.ts

Line 63 in 4584a8b

state: 'result',

As you can see here, this also happens on partial data arriving (in this situation the result of the state has a flag partial):

On changing the isPending logic to check for this flag, the execution gets cancelled correctly:

@ppisljar @dokmic Could you check this out?