Add markdownlint script to lint docs markup

Adds a new script `lint-md-docs` that runs markdownlint to lint markdown
files for proper syntax. A default `.markdownlint.json` config is
included, it will require some testing to tune.

Fixes #12426

.markdownlintignore

@@ -0,0 +1,9 @@
+bin
+build
+node_modules
+phpunit
+playground
+storybook
+test
+vendor
+wordpress

package.json

@@ -197,6 +197,7 @@
  "lint-css:fix": "npm run lint-css -- --fix",
  "lint-types": "tsc",
  "lint-md": "wp-scripts lint-md",
+ "lint-md:docs": "wp-scripts lint-md-docs",
  "package-plugin": "./bin/build-plugin-zip.sh",
  "pot-to-php": "./bin/pot-to-php.js",
  "publish:check": "lerna updated",

packages/scripts/config/.markdownlint.json

@@ -0,0 +1,8 @@
+{
+ "default": true,
+ "MD003": { "style": "atx" },
+ "MD007": { "indent": 4 },
+ "MD013": { "line_length": 9999 },
+ "no-hard-tabs": false,
+ "whitespace": false
+}

packages/scripts/package.json

@@ -53,6 +53,8 @@
  "jest-puppeteer": "^4.3.0",
  "js-yaml": "^3.13.1",
  "lodash": "^4.17.15",
+ "markdownlint": "^0.18.0",
+ "markdownlint-cli": "^0.21.0",
  "minimist": "^1.2.0",
  "npm-package-json-lint": "^4.0.3",
  "prettier": "npm:[email protected]",

packages/scripts/scripts/lint-md-docs.js

@@ -0,0 +1,46 @@
+/**
+ * External dependencies
+ */
+const { sync: spawn } = require( 'cross-spawn' );
+const { sync: resolveBin } = require( 'resolve-bin' );
+
+/**
+ * Internal dependencies
+ */
+const {
+ fromConfigRoot,
+ getArgsFromCLI,
+ hasArgInCLI,
+ hasFileArgInCLI,
+ hasProjectFile,
+} = require( '../utils' );
+
+const args = getArgsFromCLI();
+
+const defaultFilesArgs = hasFileArgInCLI() ? [] : [ '**/*.md' ];
+
+// See: https://eslint.org/docs/user-guide/configuring#using-configuration-files-1.
+const hasLintConfig = hasArgInCLI( '-c' ) || hasArgInCLI( '--config' );
+
+// When a configuration is not provided by the project, use from the default
+// provided with the scripts module. Instruct ESLint to avoid discovering via
+// the `--no-eslintrc` flag, as otherwise it will still merge with inherited.
+const defaultConfigArgs = ! hasLintConfig ?
+ [ '--config', fromConfigRoot( '.markdownlint.json' ) ] :
+ [];
+
+// See: https://eslint.org/docs/user-guide/configuring#ignoring-files-and-directories.
+const hasIgnoredFiles = hasArgInCLI( '--ignore' ) ||
+ hasProjectFile( '.markdownlintignore' );
+
+const defaultIgnoreArgs = ! hasIgnoredFiles ?
+ [ '--ignore', 'build', '--ignore', 'node_modules' ] :
+ [];
+
+const result = spawn(
+ resolveBin( 'markdownlint-cli', { executable: 'markdownlint' } ),
+ [ ...defaultConfigArgs, ...defaultIgnoreArgs, ...args, ...defaultFilesArgs ],
+ { stdio: 'inherit' }
+);
+
+process.exit( result.status );