TASK-37: dispatch struct(...) and make_array(...) on the native engine

[claude-agent-ahrzb]

Native accepted these container-construction forms at fit (DataFusion) but infer() failed on them — valid SQL the library accepted at fit time, breaking only in production.

struct(a, b)         -> ValueError: Unsupported expression: STRUCT(a, b)
struct(a AS x, ...)  -> ValueError: Unsupported expression: STRUCT(...)
make_array(a, b)     -> ValueError: Unknown function: make_array

Two distinct gaps (the ticket framing was refined after recon)

The original ticket said "native has no struct(...) dispatch in convert_function." Measurement showed that's imprecise — convert_function had a struct case, but it was dead: sqlparser parses struct(...) into a first-class SqlExpr::Struct node that never reaches convert_function. Iris rewrote the ACs to match.

AC#1 — SqlExpr::Struct arm in convert_expr

SqlExpr::Struct { values, fields } => {
    if !fields.is_empty() { /* typed STRUCT<...>(...) unsupported */ }
    let out_fields = values.iter().enumerate().map(|(i, v)| match v {
        SqlExpr::Named { expr, name } => Ok((name.value.clone(), convert_expr(expr)?)),
        other => Ok((format!("c{i}"), convert_expr(other)?)),
    }).collect()?;
    Ok(Expr::Struct(out_fields))
}

Positional → c0/c1; named (a AS x, parsed as Expr::Named) → the alias. Mirrors codegen's _convert_struct (plan.py:390) and DataFusion.

AC#2 — removed the dead struct branch in convert_function

Confirmed unreachable (sqlparser routes struct(...) to SqlExpr::Struct); deleted.

AC#3 — make_array → Expr::List in convert_function

if name == "make_array" {
    return Ok(Expr::List(args));   // same path the bracket literal [a, b] uses
}

Per-engine dispatch by design: native keys off the function name (sqlparser Function), codegen off the AST node (sqlglot exp.Array) — different parsers. The differential harness proves they agree, not that the code shape is shared.

AC#4 — the 3 xfail_on_native markers removed, all pass on both engines.

Scope note — array(...) left out deliberately

array(a, b) also fails on native (Unknown function: array) — a DataFusion alias, the same loud-gap class. It is not the pinned/tested case, and adding it means untested surface, so per the AC guidance it's excluded and flagged as a possible follow-up rather than folded in silently.

Verification

• Suite 575 passed, 9 xfailed (was 572 / 12 — the 3 flipped tests now pass on both engines).
• Mutation evidence is intrinsic: all three tests were xfail (failing) on master and pass now — the pre-fix state is the mutation.
• Diff scoped to src/expr_build.rs + tests/test_diff_types.py. Rust change → maturin develop.

🤖 Generated with Claude Code

[claude-agent-ahrzb]

Closing as obsolete: the SQLTransform line this targets has been reset (#54). The DataFusion native engine, the codegen backend, and the batch transform() path are removed; what remains is the confit-served fit-and-serve path.

Nothing here is lost — the branch and its commits stay reachable if this work is ever revived.