fix: keep null rows when paginating past a non-null cursor

[breken-ai]

What kind of change does this PR introduce?

Bug fix.

What is the current behavior?

Keyset pagination never returns rows whose sort column is null once the cursor holds a non-null value, whenever those nulls sort after the cursor. That covers first/after with AscNullsLast or DescNullsLast, and last/before with AscNullsFirst or DescNullsFirst. hasNextPage also turns false too early, so a client paging through the collection stops before the null rows.

Table::to_pagination_clause builds, per order column:

col > x  or (col is not null and x is null and <nulls_first>)

This handles a null cursor under NullsFirst. The mirror case is missing: the column is null, the cursor is not, and nulls sort last.

Repro (account(id int primary key, score int), rows (1,10) (2,null) (3,20) (4,null)):

{ accountCollection(first: 2, orderBy: [{score: AscNullsLast}]) { pageInfo { hasNextPage endCursor } edges { node { id } } } }
# ids 1, 3 · hasNextPage true · endCursor "WzIwLCAzXQ==" ([20, 3])

{ accountCollection(first: 2, after: "WzIwLCAzXQ==", orderBy: [{score: AscNullsLast}]) { pageInfo { hasNextPage } edges { node { id } } } }
# master: no edges. Expected: ids 2, 4

What is the new behavior?

The clause adds or (col is null and x is not null and <nulls_last>), so rows with null values follow a non-null cursor wherever the effective direction puts nulls last. Pages come back in the same order as the unpaginated query.

One existing expectation changes. In resolve_connection_pagination_args, "Last before w/ complex order" (orderBy: [{reversed: AscNullsLast}, {title: AscNullsFirst}], before: [3, "a"]) left out id 12 (reversed = 3, title = null). Under title AscNullsFirst, (3, null) comes before (3, "a"), so id 12 is the row right before the cursor. The last 5 rows before the cursor in forward order are ids 3, 18, 13, 8 and 12, which is what the query now returns.

Additional context

• New regression test test/sql/pagination_cursor_nulls.sql covers AscNullsLast after (plus hasNextPage), DescNullsLast after, AscNullsFirst before, and the null-cursor case that already worked.
• Proof, run with the repo's dockerfiles/db/Dockerfile toolchain (PG 17, pgrx 0.19.2):
  • On master, pagination_cursor_nulls fails. The pages after the cursor are empty and hasNextPage is false.
  • With the fix, ./bin/installcheck passes all 123 tests.
  • cargo fmt --check and cargo clippy --features pg17 -- -D warnings are clean.
• The clause has been in this shape since the Rust port.

This PR was prepared with AI assistance (Claude). I reviewed and tested the change as described above.

🤖 Generated with Claude Code

[imor]

Closing as this is 100% AI generated.