PgSelect step is not deduplicating

[jcgsville]

Summary

When doing xByRowId queries with the same constant ID, pgSelect step does not seem to correctly deduplicate

Steps to reproduce

Setup Postgraphile v5. Add a table with the ability to do a root query to fetch a single row of that table by its row ID

create table foo (id int primary key, a text);

Set graphile.explain to true in your preset

Execute a query in Ruru using aliases to query the same row twice. e.g.

query MyFoos {
  foo1: foo(id="1") {
    id
  }
  foo2: foo(id="1") {
    id
  }
}

See the diagram of the plan is similar to the screenshot above

Please let me know if it would be useful to create a minimal repro of this. I'm happy to do so

Expected results

I expect there to be a single PgSelect step in the plan

Actual results

There are 2 PgSelect steps

Additional context

Additional discussion in this discord thread:

https://discord.com/channels/489127045289476126/1325736426587033652/1325879877576032288

Possible Solution

Not sure without digging into PgSelect code

[benjie]

Likely a bug in the deduplicate method in PgSelectStep.