feat(content-blog): infer blog post date from git history (#6593)

packages/docusaurus-utils/src/gitUtils.ts

@@ -0,0 +1,92 @@
+/**
+ * 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 path from 'path';
+import shell from 'shelljs';
+
+export class GitNotFoundError extends Error {}
+
+export const getFileCommitDate = (
+  file: string,
+  {
+    age = 'oldest',
+    includeAuthor = false,
+  }: {
+    age?: 'oldest' | 'newest';
+    includeAuthor?: boolean;
+  },
+): {
+  date: Date;
+  timestamp: number;
+  author?: string;
+} => {
+  if (!shell.which('git')) {
+    throw new GitNotFoundError(
+      `Failed to retrieve git history for "${file}" because git is not installed.`,
+    );
+  }
+
+  if (!shell.test('-f', file)) {
+    throw new Error(
+      `Failed to retrieve git history for "${file}" because the file does not exist.`,
+    );
+  }
+
+  const fileBasename = path.basename(file);
+  const fileDirname = path.dirname(file);
+
+  let formatArg = '--format=%ct';
+  if (includeAuthor) {
+    formatArg += ',%an';
+  }
+
+  let extraArgs = '--max-count=1';
+  if (age === 'oldest') {
+    // --follow is necessary to follow file renames
+    // --diff-filter=A ensures we only get the commit which (A)dded the file
+    extraArgs += ' --follow --diff-filter=A';
+  }
+
+  const result = shell.exec(
+    `git log ${extraArgs} ${formatArg} -- "${fileBasename}"`,
+    {
+      // cwd is important, see: https://github.com/facebook/docusaurus/pull/5048
+      cwd: fileDirname,
+      silent: true,
+    },
+  );
+  if (result.code !== 0) {
+    throw new Error(
+      `Failed to retrieve the git history for file "${file}" with exit code ${result.code}: ${result.stderr}`,
+    );
+  }
+  let regex = /^(?<timestamp>\d+)$/;
+  if (includeAuthor) {
+    regex = /^(?<timestamp>\d+),(?<author>.+)$/;
+  }
+
+  const output = result.stdout.trim();
+  const match = output.match(regex);
+
+  if (
+    !match ||
+    !match.groups ||
+    !match.groups.timestamp ||
+    (includeAuthor && !match.groups.author)
+  ) {
+    throw new Error(
+      `Failed to retrieve the git history for file "${file}" with unexpected output: ${output}`,
+    );
+  }
+
+  const timestamp = Number(match.groups.timestamp);
+  const date = new Date(timestamp * 1000);
+
+  if (includeAuthor) {
+    return {date, timestamp, author: match.groups.author};
+  }
+  return {date, timestamp};
+};