PG->Fabric (T-SQL): `@` (absolute value) operator emitted verbatim -> `@col` parsed as a variable

[NivasSA]

PG->Fabric (T-SQL): @ (absolute value) operator emitted verbatim -> @col parsed as a variable (sibling of #287 / #296 / #300)

Description

Transpiling PostgreSQL → Fabric (and TSQL) with TranspileOptions::strict(), the
PostgreSQL prefix @ operator (absolute value) is passed through verbatim:
SELECT f1, @ f1 AS abs_f1 FROM t emits SELECT f1, @f1 AS abs_f1 FROM t.

In T-SQL @f1 denotes a scalar variable, so Fabric rejects the statement at runtime:
Sql Error 137 (Class 15 State 2): Must declare the scalar variable "@f1".

This is a sibling of the operator-verbatim issues
#287 (->),
#296 (~),
#300 (#), and of the strict()
fail-fast class #227 /
#253: strict() returns Ok(...) with
invalid SQL. The asymmetry is the giveaway — in the same run, strict() correctly
emits ABS(f1) for the function abs(f1), but passes the @ operator through
untranslated.

Root cause (pointer)

The PG→Fabric mapping translates the named function abs() to ABS(...) but has no entry
for the @ operator alias of absolute value, so it is rendered verbatim. Behavioral
localization: abs(f1) → ABS(f1) (correct); @ f1 → @f1 (verbatim).

Affected constructs

• PostgreSQL prefix @ (absolute value) operator on any numeric type (float4, float8,
  numeric, int).
• More generally: PG operator aliases of built-in functions that have a valid T-SQL
  function form but no operator→function mapping.

Repro

polyglot-sql 0.5.15, features transpile, dialect-postgresql, dialect-tsql, dialect-fabric:

# Cargo.toml
[dependencies]
polyglot-sql = { version = "0.5.15", default-features = false, features = [
    "transpile", "dialect-postgresql", "dialect-tsql", "dialect-fabric",
] }

use polyglot_sql::{Dialect, DialectType, TranspileOptions};

fn main() {
    let pg = Dialect::get(DialectType::PostgreSQL);

    // --- Flagged: strict() returns Ok(...) with invalid SQL (target = Fabric) ---
    let out = pg
        .transpile_with("SELECT f1, @ f1 AS abs_f1 FROM float4_tbl",
            DialectType::Fabric, TranspileOptions::strict())
        .unwrap();
    println!("{out:?}");
    // actual: ["SELECT f1, @f1 AS abs_f1 FROM float4_tbl"]
    //         → Fabric Sql Error 137: Must declare the scalar variable "@f1".

    // --- Contrast: the FUNCTION form already translates correctly (same run) ---
    let ok = pg
        .transpile_with("SELECT abs(f1) AS a FROM float4_tbl",
            DialectType::Fabric, TranspileOptions::strict())
        .unwrap();
    println!("{ok:?}");
    // actual: ["SELECT ABS(f1) AS a FROM float4_tbl"]
}

Expected

@ x should translate to the T-SQL built-in ABS(x) — a valid target form exists, so the
correct fix is a REWRITE, not rejection. Failing that, strict() should return Err so
callers can fall back instead of emitting a @name variable reference.

Notes

• Reproduced on polyglot-sql 0.5.15; transpiler output captured directly from transpile_with.
• Type-agnostic (the abs operator applies to every numeric type); observed on float4 and float8.
• The same generator underlies the Fabric and TSQL targets.

[tobilg]

This is fixed in the upcoming version 0.5.16 that will be available in approx. 2h

[NivasSA]

Verified, thanks. Closing the issue