create script to homogenise localised frontmatter (github#19014)

Co-authored-by: James M. Greene <JamesMGreene@github.com>

script/i18n/homogenize-frontmatter.js

@@ -0,0 +1,59 @@
+#!/usr/bin/env node
+
+// [start-readme]
+//
+// Run this script to fix known frontmatter errors by copying values from english file
+// Translatable properties are designated in the frontmatter JSON schema
+//
+// [end-readme]
+
+const { execSync } = require('child_process')
+const fs = require('fs')
+const path = require('path')
+const readFileAsync = require('../../lib/readfile-async')
+const fm = require('../../lib/frontmatter')
+const matter = require('gray-matter')
+
+const extractFrontmatter = async (path) => {
+  const fileContents = await readFileAsync(path, 'utf8')
+  return fm(fileContents)
+}
+
+// Find all content files that differ from the default branch
+// TODO: make sure this will work in an Actions workflow
+const cmd = 'git -c diff.renameLimit=10000 diff --name-only origin/main'
+const changedFilesRelPaths = execSync(cmd)
+  .toString()
+  .split('\n')
+  .filter(filename => {
+    return filename.startsWith('translations/') &&
+    filename.includes('/content/') &&
+    !filename.endsWith('README.md')
+  })
+
+changedFilesRelPaths.forEach(async (relPath) => {
+  const localisedAbsPath = path.join(__dirname, '../..', relPath)
+  // find the corresponding english file by removing the first 2 path segments: /translations/<language code>
+  const engAbsPath = path.join(__dirname, '../..', relPath.split(path.sep).slice(2).join(path.sep))
+
+  const localisedFrontmatter = await extractFrontmatter(localisedAbsPath)
+  if (!localisedFrontmatter) return
+
+  // Load frontmatter from the source english file
+  const englishFrontmatter = await extractFrontmatter(engAbsPath)
+
+  // Look for differences between the english and localised non-translatable properties
+  let overWroteSomething = false
+  for (const prop in englishFrontmatter.data) {
+    if (!fm.schema.properties[prop].translatable && localisedFrontmatter.data[prop] !== englishFrontmatter.data[prop]) {
+      localisedFrontmatter.data[prop] = englishFrontmatter.data[prop]
+      overWroteSomething = true
+    }
+  }
+
+  // rewrite the localised file, if it changed
+  if (overWroteSomething) {
+    const toWrite = matter.stringify(localisedFrontmatter.content, localisedFrontmatter.data, { lineWidth: 10000, forceQuotes: true })
+    fs.writeFileSync(localisedAbsPath, toWrite)
+  }
+})