Can't aggregate if the source question is an aggregated question

[qnkhuat]

Describe the bug
There are no fields for aggregation in questions if the source question is aggregated

To Reproduce

1. Question -> Sample -> Orders - Summary "Sum of Quantity" And "Average of total", grouped by "Created At:Month"
   
2. Save Question - Q1
3. Create a new question with the source "Q1"
4. Click Summarize -> Sum of : Notice there are no fields in the dropdown
   

Expected behavior
When clicking Summarize -> Sum of, there should be 2 fields: "Sum of Quantity" And "Average of Total"

Screenshots
If applicable, add screenshots to help explain your problem.

Information about your Metabase Installation:
Current master(c41ecda)

Severity
P2?

Additional info
A workaround is to turn the question into a model, but we also have a bug(#23248) with the model.

[flamber]

It only happens if you don't run the query (Visualize) before saving in step 2. I wrote more about it #16671 (comment).
It will cause other types of problems, dashboard filter selections etc: https://github.com/metabase/metabase/issues?q=is%3Aissue+is%3Aopen+%22result_metadata%22

[qnkhuat]

Could you try again?
I tried to visualize then save, but it's still happening.

[flamber]

@qnkhuat If you refresh the question after you have saved, then it works. Not quite sure what is going on here.

[qnkhuat]

Did some debugging and I think the problem is if BE returns result_metadata with a source="aggregation", then FE will fail to show the list.

The reason running the question before creating a new nested question works is if you run a question, BE updates the result_metadata that will remove the source property of metadata.

I think we need to check the FE to see why the presence of source creates this bug.

[daltojohnso]

This seems not to be backend and as far as I can tell -- this is intentional on the part of the FE -- well, it seems intentional to me, but the code is four years old.

We call this StructuredQuery method to generate the list of fields for this popover:

metabase/frontend/src/metabase-lib/lib/queries/StructuredQuery.ts

Line 651 in d2d076a

aggregationFieldOptions(agg: string | AggregationOperator): DimensionOptions {

That method calls this StructuredQuery method to generate a list of fields:

metabase/frontend/src/metabase-lib/lib/queries/StructuredQuery.ts

Line 1296 in d2d076a

fieldOptions(fieldFilter: FieldFilter = field => true): DimensionOptions {

There's a filter in that method to check to make sure that the field is not an aggregation:

metabase/frontend/src/metabase/lib/schema_metadata.js

Line 160 in d2d076a

export const isDimension = col =>

I think the reason this ever worked is because the FE terribly scrapes together various bits of field metadata and fails to include certain properties sometimes. I encountered this when testing #25109 and was surprised at the behavior and it took me a while to figure things out.

Is this intentional or should we open things up?

[ranquild]

I believe it should be fixed on the backend. There should be no such case that there is a different source before and after the query for first time.