Function plan_is_expr

src/sql/src/plan/query.rs:5686–5742

(
    ecx: &ExprContext,
    expr: &'a Expr<Aug>,
    construct: &IsExprConstruct<Aug>,
    not: bool,
)

}

fn plan_is_expr<'a>(
    ecx: &ExprContext,
    expr: &'a Expr<Aug>,
    construct: &IsExprConstruct<Aug>,
    not: bool,
) -> Result<HirScalarExpr, PlanError> {
    let expr_hir = plan_expr(ecx, expr)?;

    let mut result = match construct {
        IsExprConstruct::Null => {
            // PostgreSQL can plan `NULL IS NULL` but not `$1 IS NULL`. This is
            // at odds with our type coercion rules, which treat `NULL` literals
            // and unconstrained parameters identically. Providing a type hint
            // of string means we wind up supporting both.
            expr_hir.type_as_any(ecx)?.call_is_null()
        }
        IsExprConstruct::Unknown => expr_hir.type_as(ecx, &SqlScalarType::Bool)?.call_is_null(),
        IsExprConstruct::True => expr_hir
            .type_as(ecx, &SqlScalarType::Bool)?
            .call_unary(UnaryFunc::IsTrue(expr_func::IsTrue)),
        IsExprConstruct::False => expr_hir
            .type_as(ecx, &SqlScalarType::Bool)?
            .call_unary(UnaryFunc::IsFalse(expr_func::IsFalse)),
        IsExprConstruct::DistinctFrom(expr2) => {
            // There are three cases:
            // 1. Both terms are non-null, in which case the result should be `a != b`.
            // 2. Exactly one term is null, in which case the result should be true.
            // 3. Both terms are null, in which case the result should be false.
            //
            // (a != b OR a IS NULL OR b IS NULL) AND (a IS NOT NULL OR b IS NOT NULL)

            // We'll need `expr != expr2`, but don't just construct this HIR directly. Instead,
            // construct an AST expression for `expr != expr2` and plan it to get proper type
            // checking, implicit casts, etc. (This seems to be also what Postgres does.)
            let ne_ast = expr.clone().not_equals(expr2.as_ref().clone());
            let ne_hir = plan_expr(ecx, &ne_ast)?.type_as_any(ecx)?;

            let expr1_hir = expr_hir.type_as_any(ecx)?;
            let expr2_hir = plan_expr(ecx, expr2)?.type_as_any(ecx)?;

            let term1 = HirScalarExpr::variadic_or(vec![
                ne_hir,
                expr1_hir.clone().call_is_null(),
                expr2_hir.clone().call_is_null(),
            ]);
            let term2 = HirScalarExpr::variadic_or(vec![
                expr1_hir.call_is_null().not(),
                expr2_hir.call_is_null().not(),
            ]);
            term1.and(term2)
        }
    };
    if not {
        result = result.not();
    }
    Ok(result)
}