feat(blog): warn duplicate and inline authors (#10224)

Co-authored-by: OzakIOne <OzakIOne@users.noreply.github.com>
Co-authored-by: sebastien <lorber.sebastien@gmail.com>

packages/docusaurus-plugin-content-blog/src/authorsProblems.ts

@@ -0,0 +1,72 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import _ from 'lodash';
+import logger from '@docusaurus/logger';
+import type {Author, PluginOptions} from '@docusaurus/plugin-content-blog';
+
+export function reportAuthorsProblems(params: {
+  authors: Author[];
+  blogSourceRelative: string;
+  options: Pick<PluginOptions, 'onInlineAuthors' | 'authorsMapPath'>;
+}): void {
+  reportInlineAuthors(params);
+  reportDuplicateAuthors(params);
+}
+
+export function reportInlineAuthors({
+  authors,
+  blogSourceRelative,
+  options: {onInlineAuthors, authorsMapPath},
+}: {
+  authors: Author[];
+  blogSourceRelative: string;
+  options: Pick<PluginOptions, 'onInlineAuthors' | 'authorsMapPath'>;
+}): void {
+  if (onInlineAuthors === 'ignore') {
+    return;
+  }
+  const inlineAuthors = authors.filter((author) => !author.key);
+  if (inlineAuthors.length > 0) {
+    logger.report(onInlineAuthors)(
+      logger.interpolate`Some blog authors used in path=${blogSourceRelative} are not defined in path=${authorsMapPath}:
+- ${inlineAuthors.map(authorToString).join('\n- ')}
+
+Note that we recommend to declare authors once in a path=${authorsMapPath} file and reference them by key in blog posts front matter to avoid author info duplication.
+But if you want to allow inline blog authors, you can disable this message by setting onInlineAuthors: 'ignore' in your blog plugin options.
+More info at url=${'https://docusaurus.io/docs/blog'}
+`,
+    );
+  }
+}
+
+export function reportDuplicateAuthors({
+  authors,
+  blogSourceRelative,
+}: {
+  authors: Author[];
+  blogSourceRelative: string;
+}): void {
+  const duplicateAuthors = _(authors)
+    // for now we only check for predefined authors duplicates
+    .filter((author) => !!author.key)
+    .groupBy((author) => author.key)
+    .pickBy((authorsByKey) => authorsByKey.length > 1)
+    // We only keep the "test" of all the duplicate groups
+    // The first author of a group is not really a duplicate...
+    .flatMap(([, ...rest]) => rest)
+    .value();
+
+  if (duplicateAuthors.length > 0) {
+    throw new Error(logger.interpolate`Duplicate blog post authors were found in blog post path=${blogSourceRelative} front matter:
+- ${duplicateAuthors.map(authorToString).join('\n- ')}`);
+  }
+}
+
+function authorToString(author: Author) {
+  return JSON.stringify(author);
+}