message: change warning to exception
diff: @@ -2,6 +2,7 @@ import { dirname, join } from "../deps/path.ts";
  import { emptyDir, ensureDir } from "../deps/fs.ts";
  import { copy } from "../deps/fs_copy.ts";
  import { concurrent, normalizePath, sha1 } from "./utils.ts";
  +import { Exception } from "./errors.ts";
  import type { Page } from "./filesystem.ts";
  import type Logger from "./logger.ts";
  @@ -71,12 +72,12 @@ export default class Writer {
  const [previousCount, previousPage, previousHash] = previous;
  if (previousCount === this.#saveCount) {
  - this.logger.warn(
  - "The content of a page saved previously will be ovewriten. Use distinct `url` values to resolve the conflict.",
  + throw new Exception(
  + "A page will overwrite another page. Use distinct `url` values to resolve the conflict.",
  {
  + page,
  previousPage,
  - currentPage: page.src.path + page.src.ext,
  - output: dest,
  + destination: dest,
  },
  );
  }
  