/**
 * Shared Helper Functions
 * Common utilities used across validation rules.
 */
import type { ExpressionNode } from '@rcrsr/rill';
/**
 * Extract source line at location for context display.
 * Splits source by newlines, retrieves the specified line (1-indexed), and trims it.
 */
export declare function extractContextLine(line: number, source: string): string;
/**
 * Detect if expression is a bare $ (pipe variable) reference.
 * Used by IMPLICIT_DOLLAR_* rules to detect replaceable patterns.
 *
 * Returns true only for single bare $, not $var or $.field or $[0].
 * O(1) depth traversal (max 3 node levels): PipeChain -> ArithHead -> PostfixExpr -> Variable.
 *
 * Distinct from containsBareReference() in closures.ts:
 * - isBareReference(): O(1) single-node check, answers "is this exact node a bare $?"
 * - containsBareReference(): Recursive AST walker, answers "does this subtree contain any bare $?"
 *
 * @param expr - Expression node to check
 * @returns true if expr is a bare $ reference, false otherwise
 */
export declare function isBareReference(expr: ExpressionNode | null | undefined): boolean;