sortedRoutes.js

// Copied from serverless-next.js (v1.9.10)
// https://github.com/danielcondemarin/serverless-next.js/blob/master/packages/serverless-nextjs-component/lib/sortedRoutes.js

/// This file taken was from next.js repo and converted to JS.
// https://github.com/zeit/next.js/blob/canary/packages/next/next-server/lib/router/utils/sorted-routes.ts

class UrlNode {
  constructor() {
    this.placeholder = true;
    this.children = new Map();
    this.slugName = null;
    this.restSlugName = null;
  }

  insert(urlPath) {
    this._insert(urlPath.split("/").filter(Boolean), [], false);
  }

  smoosh() {
    return this._smoosh();
  }

  _smoosh(prefix = "/") {
    const childrenPaths = [...this.children.keys()].sort();
    if (this.slugName !== null) {
      childrenPaths.splice(childrenPaths.indexOf("[]"), 1);
    }
    if (this.restSlugName !== null) {
      childrenPaths.splice(childrenPaths.indexOf("[...]"), 1);
    }

    const routes = childrenPaths
      .map(c => this.children.get(c)._smoosh(`${prefix}${c}/`))
      .reduce((prev, curr) => [...prev, ...curr], []);

    if (this.slugName !== null) {
      routes.push(
        ...this.children.get("[]")._smoosh(`${prefix}[${this.slugName}]/`)
      );
    }

    if (!this.placeholder) {
      routes.unshift(prefix === "/" ? "/" : prefix.slice(0, -1));
    }

    if (this.restSlugName !== null) {
      routes.push(
        ...this.children
          .get("[...]")
          ._smoosh(`${prefix}[...${this.restSlugName}]/`)
      );
    }

    return routes;
  }

  _insert(urlPaths, slugNames, isCatchAll) {
    if (urlPaths.length === 0) {
      this.placeholder = false;
      return;
    }

    if (isCatchAll) {
      throw new Error(`Catch-all must be the last part of the URL.`);
    }

    // The next segment in the urlPaths list
    let nextSegment = urlPaths[0];

    // Check if the segment matches `[something]`
    if (nextSegment.startsWith("[") && nextSegment.endsWith("]")) {
      // Strip `[` and `]`, leaving only `something`
      let segmentName = nextSegment.slice(1, -1);
      if (segmentName.startsWith("...")) {
        segmentName = segmentName.substring(3);
        isCatchAll = true;
      }

      if (segmentName.startsWith(".")) {
        throw new Error(
          `Segment names may not start with erroneous periods ('${segmentName}').`
        );
      }

      function handleSlug(previousSlug, nextSlug) {
        if (previousSlug !== null) {
          // If the specific segment already has a slug but the slug is not `something`
          // This prevents collisions like:
          // pages/[post]/index.js
          // pages/[id]/index.js
          // Because currently multiple dynamic params on the same segment level are not supported
          if (previousSlug !== nextSlug) {
            // TODO: This error seems to be confusing for users, needs an err.sh link, the description can be based on above comment.
            throw new Error(
              `You cannot use different slug names for the same dynamic path ('${previousSlug}' !== '${nextSlug}').`
            );
          }
        }

        if (slugNames.indexOf(nextSlug) !== -1) {
          throw new Error(
            `You cannot have the same slug name "${nextSlug}" repeat within a single dynamic path`
          );
        }

        slugNames.push(nextSlug);
      }

      if (isCatchAll) {
        handleSlug(this.restSlugName, segmentName);
        // slugName is kept as it can only be one particular slugName
        this.restSlugName = segmentName;
        // nextSegment is overwritten to [] so that it can later be sorted specifically
        nextSegment = "[...]";
      } else {
        handleSlug(this.slugName, segmentName);
        // slugName is kept as it can only be one particular slugName
        this.slugName = segmentName;
        // nextSegment is overwritten to [] so that it can later be sorted specifically
        nextSegment = "[]";
      }
    }

    // If this UrlNode doesn't have the nextSegment yet we create a new child UrlNode
    if (!this.children.has(nextSegment)) {
      this.children.set(nextSegment, new UrlNode());
    }

    this.children
      .get(nextSegment)
      ._insert(urlPaths.slice(1), slugNames, isCatchAll);
  }
}

module.exports = function getSortedRoutes(normalizedPages) {
  // First the UrlNode is created, and every UrlNode can have only 1 dynamic segment
  // Eg you can't have pages/[post]/abc.js and pages/[hello]/something-else.js
  // Only 1 dynamic segment per nesting level

  // So in the case that is test/integration/dynamic-routing it'll be this:
  // pages/[post]/comments.js
  // pages/blog/[post]/comment/[id].js
  // Both are fine because `pages/[post]` and `pages/blog` are on the same level
  // So in this case `UrlNode` created here has `this.slugName === 'post'`
  // And since your PR passed through `slugName` as an array basically it'd including it in too many possibilities
  // Instead what has to be passed through is the upwards path's dynamic names
  const root = new UrlNode();

  // Here the `root` gets injected multiple paths, and insert will break them up into sublevels
  normalizedPages.forEach(pagePath => root.insert(pagePath));
  // Smoosh will then sort those sublevels up to the point where you get the correct route definition priority
  return root.smoosh();
};