Method updateBuildMatches

packages/cli/src/util/dev/server.ts:486–566

(
    vercelConfig: VercelConfig,
    isInitial = false
  )

  }

  async updateBuildMatches(
    vercelConfig: VercelConfig,
    isInitial = false
  ): Promise<void> {
    const fileList = this.resolveBuildFiles(this.files);
    const matches = await getBuildMatches(
      vercelConfig,
      this.cwd,
      this,
      fileList
    );
    const sources = matches.map(m => m.src);

    if (isInitial && fileList.length === 0) {
      output.warn('There are no files inside your deployment.');
    }

    // Delete build matches that no longer exists
    const ops: Promise<void>[] = [];
    for (const src of this.buildMatches.keys()) {
      if (!sources.includes(src)) {
        output.debug(`Removing build match for "${src}"`);
        const match = this.buildMatches.get(src);
        if (match) {
          ops.push(shutdownBuilder(match));
        }
        this.buildMatches.delete(src);
      }
    }
    await Promise.all(ops);

    // Add the new matches to the `buildMatches` map
    const blockingBuilds: Promise<void>[] = [];
    for (const match of matches) {
      const currentMatch = this.buildMatches.get(match.src);
      if (!buildMatchEquals(currentMatch, match)) {
        output.debug(
          `Adding build match for "${match.src}" with "${match.use}"`
        );
        this.buildMatches.set(match.src, match);
        if (!isInitial && needsBlockingBuild(match)) {
          const buildPromise = executeBuild(
            vercelConfig,
            this,
            this.files,
            match,
            null,
            false
          );
          blockingBuilds.push(buildPromise);
        }
      }
    }

    if (blockingBuilds.length > 0) {
      output.debug(`Waiting for ${blockingBuilds.length} "blocking builds"`);
      this.blockingBuildsPromise = Promise.all(blockingBuilds)
        .then(() => {