@wordpress/block-library/build-module/pattern/recursion-detector.js

Block library for the WordPress editor.

/**
 * THIS MODULE IS INTENTIONALLY KEPT WITHIN THE PATTERN BLOCK'S SOURCE.
 *
 * This is because this approach for preventing infinite loops due to
 * recursively rendering blocks is specific to the way that the `core/pattern`
 * block behaves in the editor. Any other block types that deal with recursion
 * SHOULD USE THE STANDARD METHOD for avoiding loops:
 *
 * @see https://github.com/WordPress/gutenberg/pull/31455
 * @see packages/block-editor/src/components/recursion-provider/README.md
 */

/**
 * WordPress dependencies
 */
import { useRegistry } from '@wordpress/data';

/**
 * Naming is hard.
 *
 * @see useParsePatternDependencies
 *
 * @type {WeakMap<Object, Function>}
 */
const cachedParsers = new WeakMap();

/**
 * Hook used by PatternEdit to parse block patterns. It returns a function that
 * takes a pattern and returns nothing but throws an error if the pattern is
 * recursive.
 *
 * @example
 * ```js
 * const parsePatternDependencies = useParsePatternDependencies();
 * parsePatternDependencies( selectedPattern );
 * ```
 *
 * @see parsePatternDependencies
 *
 * @return {Function} A function to parse block patterns.
 */
export function useParsePatternDependencies() {
  const registry = useRegistry();

  // Instead of caching maps, go straight to the point and cache bound
  // functions. Each of those functions is bound to a different Map that will
  // keep track of patterns in the context of the given registry.
  if (!cachedParsers.has(registry)) {
    const deps = new Map();
    cachedParsers.set(registry, parsePatternDependencies.bind(null, deps));
  }
  return cachedParsers.get(registry);
}

/**
 * Parse a given pattern and traverse its contents to detect any subsequent
 * patterns on which it may depend. Such occurrences will be added to an
 * internal dependency graph. If a circular dependency is detected, an
 * error will be thrown.
 *
 * EXPORTED FOR TESTING PURPOSES ONLY.
 *
 * @param {Map<string, Set<string>>} deps           Map of pattern dependencies.
 * @param {Object}                   pattern        Pattern.
 * @param {string}                   pattern.name   Pattern name.
 * @param {Array}                    pattern.blocks Pattern's block list.
 *
 * @throws {Error} If a circular dependency is detected.
 */
export function parsePatternDependencies(deps, {
  name,
  blocks
}) {
  const queue = [...blocks];
  while (queue.length) {
    const block = queue.shift();
    for (const innerBlock of (_block$innerBlocks = block.innerBlocks) !== null && _block$innerBlocks !== void 0 ? _block$innerBlocks : []) {
      var _block$innerBlocks;
      queue.unshift(innerBlock);
    }
    if (block.name === 'core/pattern') {
      registerDependency(deps, name, block.attributes.slug);
    }
  }
}

/**
 * Declare that pattern `a` depends on pattern `b`. If a circular
 * dependency is detected, an error will be thrown.
 *
 * EXPORTED FOR TESTING PURPOSES ONLY.
 *
 * @param {Map<string, Set<string>>} deps Map of pattern dependencies.
 * @param {string}                   a    Slug for pattern A.
 * @param {string}                   b    Slug for pattern B.
 *
 * @throws {Error} If a circular dependency is detected.
 */
export function registerDependency(deps, a, b) {
  if (!deps.has(a)) {
    deps.set(a, new Set());
  }
  deps.get(a).add(b);
  if (hasCycle(deps, a)) {
    throw new TypeError(`Pattern ${a} has a circular dependency and cannot be rendered.`);
  }
}

/**
 * Determine if a given pattern has circular dependencies on other patterns.
 * This will be determined by running a depth-first search on the current state
 * of the graph represented by `patternDependencies`.
 *
 * @param {Map<string, Set<string>>} deps           Map of pattern dependencies.
 * @param {string}                   slug           Pattern slug.
 * @param {Set<string>}              [visitedNodes] Set to track visited nodes in the graph.
 * @param {Set<string>}              [currentPath]  Set to track and backtrack graph paths.
 * @return {boolean} Whether any cycle was found.
 */
function hasCycle(deps, slug, visitedNodes = new Set(), currentPath = new Set()) {
  var _deps$get;
  visitedNodes.add(slug);
  currentPath.add(slug);
  const dependencies = (_deps$get = deps.get(slug)) !== null && _deps$get !== void 0 ? _deps$get : new Set();
  for (const dependency of dependencies) {
    if (!visitedNodes.has(dependency)) {
      if (hasCycle(deps, dependency, visitedNodes, currentPath)) {
        return true;
      }
    } else if (currentPath.has(dependency)) {
      return true;
    }
  }

  // Remove the current node from the current path when backtracking
  currentPath.delete(slug);
  return false;
}
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