Function resolveDevImage

packages/container/src/dev.ts:192–263

* Resolve the image to run locally: either a configured prebuilt image, or one * built locally from the service's Dockerfile. * * Unlike the cloud build, dev builds for the host architecture (no * `--platform linux/amd64`) and never pushes to a registry.

(
  options: StartDevServerOptions,
  out: DevOutput,
  span?: Span
)

 * `--platform linux/amd64`) and never pushes to a registry.
 */
async function resolveDevImage(
  options: StartDevServerOptions,
  out: DevOutput,
  span?: Span
): Promise<string> {
  const { config, workPath, entrypoint } = options;

  const entrypointRef = readString(entrypoint);
  // An entrypoint that names a Dockerfile (including the `Dockerfile.vercel` /
  // `Containerfile.vercel` opt-in markers) is built directly. Otherwise — e.g.
  // when the `container` framework preset resolves its entrypoint via
  // `<detect>` — discover an opt-in marker in the work directory. This mirrors
  // the build path (`resolveImageHandler`) so dev and deploy resolve the same
  // Dockerfile.
  const dockerfileConfigured =
    entrypointRef && isDockerfileRef(entrypointRef)
      ? entrypointRef
      : findDockerfile(workPath);
  const dockerfileRel = dockerfileConfigured ?? 'Dockerfile';
  const dockerfilePath = path.join(workPath, dockerfileRel);
  const hasDockerfile =
    dockerfileConfigured !== undefined || existsSync(dockerfilePath);

  const prebuiltImage =
    readString(config.handler) ?? (hasDockerfile ? undefined : entrypointRef);

  if (!hasDockerfile) {
    if (!prebuiltImage) {
      throw new Error(
        'Container service must specify an entrypoint: a prebuilt OCI image ' +
          'reference, or a Dockerfile path to run with `vercel dev`.'
      );
    }
    span?.setAttributes({ 'container.dev_mode': 'prebuilt' });
    emit(out, `▲ container  vercel dev: using prebuilt image ${prebuiltImage}`);
    return prebuiltImage;
  }

  if (!existsSync(dockerfilePath)) {
    throw new Error(
      `Dockerfile not found at "${dockerfilePath}" for container service.`
    );
  }

  const serviceName = options.service?.name ?? 'service';
  const tag = devImageTag(serviceName);
  const contextDir = path.dirname(dockerfilePath);

  // Forward the project build env as `--build-arg`s so Dockerfile `ARG`s work
  // in dev too, matching the cloud build.
  const buildArgFlags: string[] = [];
  const buildEnv = (options.meta?.buildEnv ?? {}) as Record<
    string,
    string | undefined
  >;
  for (const [key, value] of Object.entries(buildEnv)) {
    if (typeof value === 'string') {
      buildArgFlags.push('--build-arg', `${key}=${value}`);