Enum LimitExpr 

pub enum LimitExpr {
    Literal(u32),
    Placeholder(u16),
    Expr(Box<Expr>),
}

v7.9.24 — LIMIT / OFFSET value. Integer literal at parse time or a placeholder $N resolved during extended-query Bind. mailrs migration follow-up H2.

v7.39 (round 305) — no longer Copy/Eq: the Expr variant boxes an arbitrary row-count expression. Losing Copy is deliberate — it made the compiler point at every site that used to duplicate a row-count out of the AST, which is exactly the set that must not bypass the resolution pre-pass.

Variants

Literal(u32)

LIMIT 10 — value known at parse time.

Placeholder(u16)

LIMIT $N — the 1-based parameter index, resolved against the bind values when the prepared statement executes.

Expr(Box<Expr>)

v7.39 (round 305, V23) — LIMIT (SELECT 4) / LIMIT greatest(2,3): a row-count expression that isn’t constant, so it can’t be folded at parse time. Evaluated once, before dispatch, by the engine’s resolve_limit_exprs pre-pass, which rewrites it to Literal (or to None for a NULL result, PG’s “no limit”). No execution path may see this variant — as_literal would report None, which every row-count reader takes to mean “unlimited”, i.e. the whole table.

Implementations

impl LimitExpr

pub fn as_literal(&self) -> Option<u32>

Convenience for the simple-query path where no placeholders can possibly exist. Returns the literal value or None if this is a placeholder (caller must surface as Unsupported).

v7.39 (round 305) — None is read by every row-count consumer as “no limit”. An unresolved LimitExpr::Expr reaching here would therefore silently return the whole table, so the engine’s resolve_limit_exprs pre-pass rewrites the variant away before dispatch. The assertion makes a missed nesting site fail loudly in every test build rather than quietly widening a result set.

Trait Implementations

impl Clone for LimitExpr

fn clone(&self) -> LimitExpr

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for LimitExpr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Display for LimitExpr

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for LimitExpr

fn eq(&self, other: &LimitExpr) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for LimitExpr