Propagate null through agtype arithmetic operators

[MuhammadTahaNaveed]

The scalar branch of agtype_add lacked an AGTV_NULL case and fell through to the scalar-scalar concat path, so null + 1 produced the two-element list [null, 1] instead of null. This surfaced most visibly inside a list comprehension projection (e.g. [x IN [1, null, 2] | x + 1] yielded [2, [null, 1], 3]) because there both operands are typed agtype and bypass the agtype_any_add wrapper that already short-circuits on null.

The sibling operators (-, *, /, %, ^, unary -) had the same gap but surfaced as "Invalid input parameter types" errors rather than concats.

Short-circuit all seven functions to SQL NULL when any operand is AGTV_NULL. SQL NULL (not a wrapped AGTV_NULL scalar) matches AGE's existing convention: RETURN null AS v already yields SQL NULL at the row level, and agtype_any_add already returns PG NULL for AGTV_NULL input, so the two operator-resolution paths stay indistinguishable. List aggregation re-packs SQL NULL entries as AGTV_NULL, so [x IN [1, null, 2] | x + 1] now renders as [2, null, 3].

[Copilot]

Pull request overview

Note

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Propagates SQL NULL through scalar agtype arithmetic operators to match openCypher semantics and prevent unintended concatenation / type errors, especially in list comprehension projections.

Changes:

• Add early-return PG_RETURN_NULL() handling for AGTV_NULL operands across + - * / % ^ and unary -.
• Extend regression coverage for list comprehensions to ensure null propagation across arithmetic operators.
• Add/adjust agtype regression expectations to reflect SQL NULL results for arithmetic involving null.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/backend/utils/adt/agtype_ops.c	Adds AGTV_NULL short-circuit returns for scalar arithmetic operators.
regress/sql/list_comprehension.sql	Adds regression queries covering null propagation in list comprehension projections.
regress/sql/agtype.sql	Adds regression queries for arithmetic operators with null operands.
regress/expected/list_comprehension.out	Updates expected results to show null propagation instead of sublists/errors.
regress/expected/agtype.out	Updates expected results to show SQL NULL outputs for null arithmetic.

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[Copilot]

These tests pass a bare string literal as the RHS (type unknown), which relies on implicit coercion/operator resolution and can make the intent of testing the scalar agtype operator path less explicit. Consider casting the RHS to agtype (e.g., '1'::agtype) so the tests more directly exercise agtype-vs-agtype arithmetic and are less sensitive to changes in implicit casts.

Suggested change

	SELECT 'null'::agtype ^ '1';
	SELECT 'null'::agtype ^ '1'::agtype;

[Copilot]

The identical AGTV_NULL short-circuit block is now duplicated across multiple operator functions (add/sub/mul/div/mod/pow/neg). To reduce repetition and keep behavior consistent over time, consider factoring this into a small helper (e.g., a static inline function or macro) used by each operator.