Function fire_row_trigger 

pub fn fire_row_trigger(
    function: &FunctionDef,
    new_row: Option<Row<'static>>,
    old_row: Option<&Row<'static>>,
    table_name: &str,
    columns: &[ColumnSchema],
    params: &[Value<'static>],
    default_text_search_config: Option<&str>,
    is_after: bool,
    tg: &TgMeta<'_>,
    notice_sink: Option<&NoticeSink>,
) -> Result<(TriggerOutcome, Vec<DeferredEmbeddedStmt>), TriggerError>

Fire a single row-level trigger.

is_after is true for AFTER triggers; the executor enforces “NEW is read-only” by rejecting NEW.col assignments in that case. AFTER trigger return values are ignored by callers; the returned TriggerOutcome just carries the (possibly untouched) NEW row for symmetry.